FUNDAMENTALS OF MICROBIOLOGY-For Various Competitive Exams.

1. MICROBIOLOGY: INTRODUCTION

i.Micro-biology is study of microorganisms like viruses, Bacteria, Protozoa, 1-celled algae and 1-celled fungi etc. Antonie van Leeuwenhoek of Holland, Louis Pasteur of France, Robert Koch of Germany and Joseph Lister of England were earlier, workers in Microbiology. Leeuwenhoek is recognized as 'pioneer' worker in microbiology, he discovered bacteria for the first time as 'animalcules' or the 'wretched beastes'. Pasteur was fist to study role of microorganisms in fermentation process involved in wine preparation. Koch studied anthrax disease, caused by bacteria Bacillus anthracis. On the basis of his study Koch proposed Law of Pathogenicity, which was later on recognized as Koch's Postulates. Koch's Postulates are not applicable for viruses & organisms causing TB and leprosy. Lister introduced antiseptic surgery and also prepared culture of bacteria first time.

ii.The two major research institutes of microbiology in world are: Pasteur Institute of Microbiology in Paris, France and Lister Institute of Microbiology, England. Workers at Lister Institute discovered 'naked' bacteria i.e. bacteria without cell of mucopolysaccharide complex. They were called 'L-form' of bacteria, named after Lister Institute. Mycoplasma like organisms, PPLO, is called L-form of Bacteria.

iii.Triple Antigen Programme includes, immunization against Diptheria, Pertusis (Whooping cough) and Tetanus. It is also called D.P.T. Oral drops of polio are delivered separately. BCG vaccines are first vaccines given to new borns after 3-4 weeks of birth. Vaccines of: Polio was discovered by Salke; Small pox by Jenner, BCG by Calmett-Guire; Anthrax by Koch and Rabies by Pasteur. Vaccines of anthrax were prepared first. Pasteur, for developing vaccines of rabies was rewarded handsomely by Czar of Russia.



2. MICROBIOLOGY: STUDY OF VIRUSES

2a) Viruses: Introduction

i.Study of viruses is called virology and Beijerinck is recognized as 'father of virology'. He reported enormous power of multiplication of viruses inside host cell. He also studied mechanism of nitrogen fixation by microorganisms like bacteria.

ii.The term 'virus' has been derived from Greek word 'virion' which means 'poison'. Viruses are defined as hyperparasites and 'filterable entities' not having any cellular organization and defined as hyperparasites and 'filterable entities' not having any cellular organization and because of this cell theory is not applicable on them. They are thus exceptions to cell theory. They form crystals when taken out of the host cell. This shows non-living nature of viruses, which was first revealed by Stanley while working on 'Tobacco Mosaic Virus'. Nucleoprotein structure of viruses was first studied by Bawden & Pierre. In nucleoprotein structure of viruses, core of nucleic acid is surrounded by coat of protein. Viruses are unique as they contain only one type of nucleic acid. Mutation in viruses was first reported by Delbruck. Mutation and enormous power of reproduction confirm living nature of viruses. Viruses are thus the only entities, which have characters of non-living and living entities both. They are thus 'connecting links' between non-living entities and lining entities.



2b) Viruses: Historical Studies

Studies in viruses started with independent works of Pasteur and Adolf Mayer. Pasteur prepared vaccines of rabies virus and used the term 'virus' for first time. Mayer reported mosaic like spots on leaves of tobacco plant infected with virus. He described the virus as Tobacco Mosaic Virus [TMV]. Ivanowski passed the cell sap of infected tobacco leaves through bacteria proof bacteria proof filter and sprayed the filtrate on healthy leaves. Mosaic spots appeared again. Ivanowski through his experiment described viruses as filterable entities. Famous conclusion of Beijerinck about viruses i.e. 'contagium vivum fluidum' means sap retains the infection of viruses (living fluid infectant). Takami of Holland studied transmission of viruses through various agencies. He observed that insects are important agencies in transmission of viruses. Insects that transmit viruses are called 'vertors'. Viruses-vector relationship is highly specific.

Culture of viruses was prepared for the first time by Ender. It was poliomyelitis virus. Hershey and Chase observed that nucleic acid is the infective part of virus. They selected Bacteriophages for their experiment. Bacteriophages are DNA containing viruses which attack bacteria. They were discovered by Twort; further studies were made by DeHerelle. Experiment of Hershey & Chase is another example which confirms status of DNA as genetic material. Safferman & Morris discovered 'Cyanophages' i.e., viruses which attack blue green algae like Lyngbya, Phormidium & Plectonema. They are also called LPP-1 on the basis of hosts. Mycophages were discovered by Sinoten. They contain ds RNA.

Issac & Lindeman discovered a protein called Interferon secreted by host cells against infection of viruses. They selected cold virus for their experiment. Gibbs described viruses in coded form which is called 'Cryptogram of viruses' Cryptogram of viruses is based on 4 pairs of characters:



First pair : Type of nucleic acid in virus i.e. R or D

Number of thread in nucleic acid 1 or 2

Second pair : Molecular weight of viruses in millions i.e. 2

Percentage of nucleic acid of the viruses 5

Third pair : Shape of the virus in total i.e. E (elongeted) or S (spiral) or

X (unknown)

Shape of the protein coat of the virus E or S or X

(E' means elongated structure or rod shaped structure with blunt ends)

Fourth pair : Host/vector i.e. S (seed plant), I(invertebrate), V(vertebrate),

B(bacterium), Fu(fungus), Di(diptra), Af(aphid), Zero or 0 (novector),

X(unknown vector) Vector of the virus X



Thus, for example R/1; 2/5; E/E; S/X is cryptogram of TMV.

For Polia Virus (Poliovirus Primus) cryptogram is R/1; 5/30; S/S; V/O.

For Influenza Virus (mixovirus influenzae) R/1; 2-3/10; S/E; V/O.

For T4 phage D/2; 130/40; X/X; B/O.



2c) Viruses: Some Terms

i.A complete virus having a core of nucleic acid and coat of protein is called virion. Protein coat of the virus is termed as capsid; units of capsid are capsomeres. A virus drops its infective part i.e., nucleic acid alone inside host cell; empty protein coat remains outside. This empty protein coat, which remains outside the host called ghost protein, disappears later on. Raw material for new protein coat of the progeny viruses is contributed by the host.

 A few proteins in some viruses are enzymatic in functions e.g. lysozyme in bacteriophages, reverse transcriptase(RNA dependent DNA polymerase) in retrovituses, neuraminidase in influenza virus etc.

ii.Viriod: Subviral agent having infectious nucleic acid alone is called viroid. Viroids are RNA & particles lacks protein coat. Spindle disease in photo tuber is caused by viroid, which is PSTV. Viroids were discovered by Diener & Rayner.

iii.Prion or Slow Virus: Protein macromolecules causing infections are called prions. They lack ucleic acids. Scrappes & Kuru diseases (Severe brain infection) is sheep are caused by prions. They were first reported by Priusner who was awarded Nobel Prize for reporting Mad Cow disease caused by PrP (prion related protein). Bovine spongiform encephalopathy or Creulzfeldt Jacob disease (a type of insanity in young people), Kuru disease (the laughing death), Alzheimer's disease are caused by prions. In 1976 D.C.Gujdusek was awarded Nobel Prize for his work on prion based diseases.

iv.Viruses transmitted by insects are called Arboviruses. Viruses causing Dengue, encephalitis etc are arboviruses.

v.Viruses which contain ss-DNA are called 'Gemini viruses'. X174 phages are geminiviruses. They were reported by Sinsheimer.

vi.Viruses which enter inside host cell as intact structures, are called Adeno viruses. Well defined protein coat is absent in Adenoviruses.

vii.Virusoids or Satellilte RNAs (Rundle et. Al 1981). These are small circular RNAs similar to viroids, but are located inside the protein coat of a true virus. Virusoids required the assistance of virus for their replication.



2d) Viruses: Classification and Nomenclature









































Earlier it was believed that plant viruses i.e. Phytophagineae contain RNA whereas animal viruses i.e. Zoophagineae contain DNA. This is, however, no more correct now. The only thing which is true about viruses is presence of only one type of nucleic acid. Cold virus i.e. Rhinovirus and poliovirus i.e. Enterovirus is together placed under Picorna virus.



2e) Viruses: Disease on Plants – Symptoms

i.Mosaic like spots may develop on leaves.

ii.Leaves may show rolling or curling.

iii.Leaves may show loss of chlorophyll (Chlorosis) or death of tissues (necrosis).

iv.Plants may show abnormal or stunted growth.

v.Plants may show uncontrolled cell division i.e. hyperplasia(cell number increase) and unwanted swelling i.e. Hypertrophy in host.

vi.Plants may show loss of entire inflorescence or flowers may become green i.e. virescence in flowers.



2f) Viruses: Some Common Viral Diseases

1. Plant Viral Diseases. Tobacco Mosaic, Potato Mosaic Pumpkin Mosaic, Apple Mosaic, Tulip Mosaic (Broken Tulip), Wheat Mosaic Streak, Bhindi Yellow Vein Mosaic, Potato Leaf Roll, Tobacco Leaf Curl, Papaya Leaf Curl. Banana Bunchy Top, Tomato Bunchy Top, Rice Tungro etc.



2. Animal Viral Diseases. Foot and Mouthm, Enquine encephalitis, Rinderpest, Kysanur Forest Disease (KFD) of monkeys (also humans), New Castle or Ranikhet of Fow].



3. Human Viral Diseases. Poliomyelitis, Rabies, Mumps, Measles, German Measles, Chickenpox, Smallpox (eradicated), Dengue, Encephalitis, Common cold, Flu, some gastrointestinal diseases, Yellow Fever, Herpes, Hepatitis, SARS, AIDS.



Some Important Modern Viral Diseases



1. Cancer or Carcinoma:

Despite the fact that virus causing cancer is yet to be identified, still cancer is considered like a viral disease because of typical viral symptoms like Hyperplasia & hypertrophy, are reported in cancer. Certain genes called proto-oncogenes (c-onc) are present in human cells, which are involved in normal cell function. Mutation of proto-oncogenes may give rise to oncogenes, which stimulate cell division leading to an uncontrolled growth of the cells causing cancer. All retoveiruses and some DNA containing viruses (such as poxvirus, adenovirus, Herpes virus, hepatitis-B virus etc.) possess oncogene (v.onc) in their genome. These viruses are potential cancer producing pathogens. Study of cancer is called Oncology. Temin and Baltimore's studies on Rous sarcoma virus [RSV] have provided new dimensions in the knowledge of cancer. RSV is RNA containing virus and RNA of RSV forms DNA inside host cell through reverse transcription or 'Teminism'. Newly formed DNA develops malignant tumours in host. Harmful tumor is called malignant tumours whereas tumours, which are not harmful, are termed as benign tumours. Are lethal in advanced stage.







2. Acquired Immunodeficiency Syndrome (AIDS):

AIDS is a viral disease in which our acquired immunity defense system is gradually shattered, and the patient dies of multiple infectious diseases. The first indication of AIDS disease came to light in USA in 1981 amongst a group of young homosexuals who were addicts of herion and other narcotics. Luc Montagnier (1983) and Robert Gallo (1984) discovered that a new type of retrovirus is the causative pathogen of AIDS. In 1986, The International Committee of virus Nomenclature (ICVN) named the AIDS virus as Human Immunodeficiency Virus (HIV).

Although AIDS is hardly a two and half decades old disease, it has spread virtually all over the world, becoming pandemic. According to the estimates of world Health Organization (WHO), about 52 million people in the world harbour HIV and thousands of new cases are detected every day. In India HIV infection was first detected in 1986 in some sex workers of Tamil Nadu. Since then, about 4 million cases have been detected and infection is fast spreading.



Structure of HIV:

HIV is a spherical, enveloped virus of about 90-120 nm diameter. Its genome consists of a single stranded RNA filament segmented into two identical filaments and associated with a 'reverse transcriptase enzyme'. Due to the presence of two identical filaments of RNA, HIV is considered to be 'diploid'. The envelope is comprised of a lipid bilayer derived from host cell membrane, and projecting, knob like glycoprotein spikes with pedicels formed of virus coded glycol-proteins (gp).



Pathogenesis and Symptoms:

The sentinels of our defense system are a type of white blood cells called lymphocytes. These cells are of different types to play different roles in acquired immunity. One type of lymphocytes called T4(TH) lymphocytes, play the crucial role in activation of other components of the immune system and production of antibodies. HIV attacks T4 lymphocytes and destroy them. As a result the T4 lymphocyte count in blood gradually diminishes (< 200). From the blood plasma the virus also permeates into other body fluids like semen, vaginal fluids saliva, tears, urine, sweat, breast milk etc. Gradual destruction of T4 lymphocytes through several years ultimately leads to a full blown AIDS disease, during which a patient suffers from persistent fever and diarrhea, loss of appetite and weight, weakness and fatique, body pain, dry cough, white lesions in mouth and alimentary canal and warts upon anus and genitals. Eventually, the patient loses immunity and dies of multiple infectious diseases.



Transmission:

HIV is present in blood and other body fluids of infected persons. Hence it is transmitted from one to another person through activities involving exchange or transfer of body fluids. Thus, HIV is primarily transmitted through sexual activities. Unprotected sex, sharing of syringes and needles by intravenous drug addicts, use of unsterilized syringes by doctors and health workers etc. are responsible for transmission of HIV. Transfusion of infected blood and blood products, transplantations from infected to healthy one through breast milk feeding after birth are the other potential mode of transmission of HIV.



Diagnosis:

Some genes of HIV genome code for synthesis of some antigens which are released into the blood by infected T4 lymphocytes. The immune system of body produces antibodies against these antigens, which can be detected by serological test called Elisa (Enzyme Linked Immunosorbent Assay), western blotting and PCR polymerase reaction test are the confirmatory test.

Symbol used to describe AIDS disease is ' ' (red ribbon). Noted Hollywood star Rock Hudson & Lawn Tennis Player Arthur Ashe of US were notable AIDS-causalities.

NARI (National AIDS Research Institute Puna).

NACO (National AIDS Control Organisation).

ARV (Anti Retro Viral Drug).

Prevention and Treatment:

General precautions such as safer sex and extensive use of condoms, strict screening of blood and blood products used for transfusions and tissue and organ transplantations, and extensive health education can prevent AIDS. December, 1 is observed as World's AIDS Day to arouse general awareness amongst people about HIV infection.

At present, there is no effective drug to save the immune system of AIDS patient from collapse. However, there are some drugs which are known to delay the progress of AIDS. These include Zidovudine (Azidothymidine-AZT), XQ-9302, Amphotericine-B and its methyl ester etc.



3. Pox:

Following types of pox diseases are reported in man:

Small Pox : Caused by DNA containing Pox viridae, Varoila.

Chicken Pox : Caused by DNA containing Herpes Virus, Vacicella.

German Pox : Caused by RNA containing Para influenza virus, Rubella.

Measles or Khasra : Caused by RNA containing Para influenza virus or Paramyxoviridae with minus strand RNA. AS already mentioned, vaccines of small pox were prepared by Jenner. Earlier small pox was very lethal disease in epidemic form in India. Officially, it has been eradicated from India with the help of WHO.



Natural Defenses against Viral Infections:



1. Interferons (Isaacs and Lindenmann, 1957). Interferons are antiviral proteins (a class of glycoproteins) which diffuse out from infected cells, enter into the cells in the neighbourhood and impart a defense mechanism to these cells against viral infections by inhibiting the synthesis of viral proteins. These are therefore used for therapeutic and preventive purposes in viral infections, interferons are always secreted by host cells against viral infection.



2. Body Immunity. Viruses are good antigens to induce active production of specific antibodies (by lymphocytes).



3. Immunoprophylaxis – Vaccines: Vaccines contain inactivated (attenuated) virions, which cannot cause the concerned diseases, but still act as antigens to induce antibody production by the immune system of the body.



4. Chemotherapy – Antiviral Drugs: The chemotherapeutic agents antibiotics which are used in the treatment and control of bacterial diseases are ineffective for viral diseases. However, some antiviral drugs have been prepared. These include (i) Thiosemicarbozone (for treatment and prevention of smallpox), (ii) Ribavirin or Virozole (for influenza),
(iii) Deoxyuridines, Acylovir (for herpes), (iv) Foscarnet (for hepatitis-B) etc.



2g) Viruses: Study of Bacteriophages

i.Discovery of bacteriophages is associated with Twort when he reported viral disease in bacteria. The term bacteriophages was coined by De Herelle. They are viruses, which attack bacteria. A typical bacteriophage looks like a tadpole/sperm comprising a hexagonal head of protein and a tail also a protein they show binal symmetry. Head is 1000A long and 650A in width; length of the tail is 1000A. Thus, head and tail are equal in length. Infective part of the bacteriophage in most of the cases is ds-linear DNA and it is present in hexagonal head. Joint of head and tails is neck, which is covered by collar of protein. Tail ends in end plate that develops 3 pairs of tail fibers of protein. Bacteriophages that attack E.coli are called coliphage or T-phages. They were numbered as T1, T2, T3, T4, T5, T6, T7 etc by Delburck, T2, T4, T6 etc are T-even phages T1, T3, T5, etc or T-odd phages.

ii.A bacteriophage comes into contact with the bacterial (host) cell through tail fibres. A passage is created in the host cell once the mucocomplex cell wall of bacteria is broken by lysozyme of bacteriophage. Once the passage is created, ds-linear DNA of bacteriophage is dropped inside the host cell. Empty protein coat i.e. Ghost protein remains out the host cell and disappears later on. Infective part or genetic material in X174 phages is ss circular DNA and it is RNA in MS-2 & R17 phages.

iii.Phage DNA dropped inside host cell may be virulent or temperate. Bacterial cell is destroyed if phage DNA is virulent, bacterial cell is not destroyed is phage DNA is temperate.

iv.Destruction of bacterial cell by virulent phage DNA is called lysis. The sequence of events leading to lysis of bacterial cell are:

Virulent phage DNA dropped inside bacterial cell.

Multiplication of phage DNA inside host cell i.e. Formation of prophage. Formation of complete phages. (End of latent period or period of eclipse of phages).

Destruction or lysis of bacterial cell (Total time: 15-20 minutes).*

v. A bacterial cell is not destroyed if phage DNA is temperate. Temperate phage DNA is attached with host DNA; this is called lysogeny. A lysogenic bacterial cell behaves normally till temperate phage DNA is attached. Lysogeny in bacteria was first reported by Lwoff. Lwoff also coined the term -phage for those phages in which tail terminates into single tail fibre.

Lysogeny may be of 3 types. They are -phage lysogeny; P1-phage lysogeny and mu-phage lysogeny. In -phage lysogeny, temperate phage DNA is attached with bacterial DNA at specific place i.e. at 'gal' & 'bio' genes of bacterial DNA. In P1-phage lysogeny, temperate phage DNA is attached with any place other than gal's genes. In mu-phage lysogeny, temperate phage DNA is never attached with bacterial DNA, remain in bacterial cytoplasm as plasmid.

A lysogenic bacterial cell shows different behaviour when exposed to different dosages of UV rays:

































3. Microbiology: Study of Bacteria

3a) Bacteria: Introduction

i.Study of Bacteria is called 'Bacteriology'. Leeuwenhoek is recognized as pioneer worker in Bacteriology. Pasteur, Koch & Lister are other earlier workers in Bacteriology.

ii.The term bacteria were coined by Ehrenberg for the smaller 'animalcules' or the 'wretched beasts' of Leeuwenhoek. Bacteria are found everywhere and in all sorts of climates however they do not survive in acidic medium of Pickle solution or highly concentrated sucrose solution due to plasmolysis.

iii.Bacteria activity is reduced greatly at low temperature; this explains why foodstuff remains safe for longer period in cold devices like fridge and refrigerators etc. Bacteria behave in different manner in different range of temperature.























3b) Bacteria : Forms

i.On the basis of shape, bacteria may be cocci (Singular coccus), Bacilli (Bacillus), Vibrio, Spirillum etc. Cocci are spherical bacteria, smallest in size. They may be single (monoococucus), in pairs (Diplococcus), in chains (streptococcus), in bunches (staphylococcus) or cuboid (sar cinnae). Bacteria causing pneumonia are Diplococcus Bacilli are rod shaped bacteria they may be single or in chains (Streptobacilli). Majority of parasitic bacteria are rod shaped bacteria. Streptobacilli surrounded by mucilaginous sheath form Zoogloea. Vibro are comma shaped bacteria. Bacteria causing cholera are vibrio bacteria. Spirillum and spirochaete are zigzag spring like bacteria, Spirillum volutans is recognized as largest bacteria. The terms like coccus, bacillus, vibrio etc were coined by Mueller.

ii.On the basis of cilia, a bacterial cell may be:

Atrichous : Bacterial cell without cilia.

Monotrichour : Bacteria cell with single cilia.

Lopotrichous : Bacteria cell with tuft of cilia at one end.

Cephalotrichous : Bacterial cell with tuft of cilia at both the ends.

Amphitrichous : Bacterial cell with one cilia at both the ends.

Peritrichous : Bacterial cell with cilia throughout the body.



Bacteria causing cholera disease is comma shaped & Lophotrichous.

iii.On the basis of nutrition, bacteria may heterotrophy or autotroph. Heterotroph bacteria are further divided as saprophytic bacteria & parasitic bacteria. Similarly, autotroph bacteria are further divided as chemosynthetic and photosynthetic bacteria.

Bacteria, which obtain their food from dead organic matter, are saprophytic bacteria. They perform significant role of decomposers in ecosystem. Bacteria, which obtain their food from other living entity, are called parasitic bacteria. The living entity, which provides food to parasite, is termed as host. Host-parasite relation is specific. Parasite is called pathogen when it spreads in host.

Bacteria, which obtain their food through the inorganic reactions in which they participate, are called chemosynthetic bacteria. They are named after the inorganic reactions, us that they are involved. Thus, N-Bacteria S-Bacteria & Fe-Bacteria etc are examples of chemosynthetic bacteria. Chemosynthetic bacteria are basically autotroph but do not require pigment chlorophyll for energy requirement. Chemosynthetic bacteria will survive alone if chlorophyll pigment disappears from the world; rest will perish.

Bacteria, which obtain chemical energy through glucose formation, are called photosynthetic bacteria. They are autotrophs and depend on chlorophyll like pigments i.e., Bacteriochlorophyll & chlorobium chlorophyll (Bacterio viridies) for glucose formation. Green-S-Bacteria, Purple-S-Bacteria & Rhodospirillium etc. are examples of photosynthetic bacteria.



Comparison between normal and bacterial photosynthesis

Normal Photosynthesis

Bacterial Photosynthesis

1. Raw materials are CO2 & H2O

1. Raw materials are CO2 & H2S

2. H for reduction of CO2 into glucose comes from H2O

2. H- for reduction of CO2 into glucose comes from H2S.

3. Principal pigment is chlorophyll a

3. Principal pigment Bacteriochlorophyll a.

4. Intermediate H-acceptor is NADP

4. Intermediate H-acceptor is NAD.

5. PS I & PS II both are present in light phase.

5. PS I only is present in light phase; PS II is absent.

6. O2 is released as by product

6. S is released as by product

7. Biochemical reaction

6CO2 + 12H2O = C6H12O6+6H2O+6O2

7. Biochemical reaction.

6CO2 + 12H2O = C6H12O6+6H2O+12S

Generalised equation for both of the above

6CO2 + 12H2A = C6H12O6 + 6H2O + 12A

A may be oxygen or sulfur.



Photosynthesis in bacteria was first studied by Van Neil of Germany who was first to support the idea of Robino Hill that O2 released in normal photosynthesis comes from H2O and not from CO2.



3c) Bacteria: Disadvantages

Bacteria are our 'foes' as they are associated with several diseases of plants and animals including man due to parasitic mode of nutrition of some bacteria. Bacterial attack is less severe on plants than it is on animals.

Important bacterial diseases on plants are:

(a)Canker of Citrus (citrus canker) Xanthomonas citri

(b)Angular leaf spot of cotton X. malvacearum

(c)Fire blight of apples Erwinnia amylovora

(d)Crown gall of crops Agrobacterium tumefaciens

(e)Tondu of wheat Corynebacterium tritici

Important bacterial diseases on man are:

(f)Cyphillis Tryponema pallidum

(g)Plague (Black Death) Pasteurella pestis (Y. pestis)

(h)Chlorea Vibrio cholerae

(i)Anthrax Bacillus anthracis

(j)Pneumonia Diplococcus pneumonae

(k)Tuberculosis (TB) Mycobacterium tuberculoses

(l)Typhoid (Enteric fever) Salmonella typhi

(m)Bacterial dysentery Bacillus dysentrae (Shigella)

(n)Amoeboid dysentery Entamoeba histolytica (Protozoa)

(o)Tetanus (Lock jaw) Closteridium tetani

(p)Ptomaine (deadly food poisoning) Closteridium botulinum

(q)Leprosy Bacillus lepri (Mycobacterium lepri)

(r)Diptheria Corynebacterium diptherae

(s)Erysepalas (deadly blood Streptococcus

Poisoning; Death of RBC's)

(t)Whooping cough Bordetella partusis

(u)Gonorrhoea Neisseria gonorrhoae

Bacterial diseases like cholera, typhoid, dysentery etc are water borne diseases: tuberculosis, plague etc are air-borne diseases whereas disease like tetanus spreads through wounds. Syphilis is transmitted through sexual contact. Transmission of leprosy through contact is a matter of dispute. India based Mother Teresa was awarded Nobel Prize for her service to leprosy patients in West Bengal and other parts of India.



3d) Bacteria: Advantages:

Bacteria are our friends as they are associated with several advantages in various forms. Some of them are:

i.Bacteria & Ecosystem: Saprophytic bacteria along with saprophytic fungi perform useful role of decomposers in ecosystem. Decomposition of organic matter in absence of O2 is called putrefaction and breakdown of organic matter in presence of O2 is called decay. Highly un-decomposed organic matter is litter; partly decomposed organic matter is humus and highly decomposed organic matter is called humus.

ii.Bacteria & Industry: Lactobacillus laciti and Streptococcus lacti convert milk into curd. Acetobacillus aciti changes sugar solution into vinegar. Flavour in tea leaves by Micococcus condensa and in tobacco leaves by Micococus megatherium develops due to fermentation activity of bacteria. Retting involves separation of plant fibers after decomposition of non-cellulosic materials by various species of Closteridium like C.butyricum and C.felsineum.

iii.Bacteria and N-cycle system: Nitrogen is first essential element in terms of requirement for proper growth of plants. It is required in protein synthesis, chlorophyll synthesis and also in synthesis of nucleic acids. Plants cannot utilize molecular nitrogen directly. The plants mainly in the form of nitrates absorb it. Nitrogen changes into nitrate via ammonia formation. Some bacteria control N-cycle, which comprises Nitrogen fixation, Nitrification and Denitrification. Nitrogen fixation involves conversion of N2 into ammonia. Bacteria which participate in N-fixation are Closteridium, Azotobacter and Rhizobium etc. Closteridium and Azotobacter and asymbiotic biological N fixing bacteria whereas Rhizobium is symbiotic biological N-fixing bacteria are present in root nodules of Leguminous or papilionaceous plants. Klebsiella is leaf nodule N-fixing bacteria. Frankia is non-leguminous N-fixing bacteria 'nif' genes control biological N-fixation. Mechanism of biological N-fixation by bacteria was first studied by Heijerinck whereas Winogradasky studied biological N2 fixation by some blue green algae.

Conversion of NH3 into nitrite is termed as initial stage of Nitrification. A bacterium which participates in initial stage of nitrification is nitrosomonas Conversions of nitrite into nitrate is called final stage of nitrification. Nitrobacter is the bacteria which participates in final stage of nitrification.

Release of Nitrogen from Macromolecules of Nitrogen is called denitrification. Bacillus denitrificans is the bacteria involved in denitrification. The summary of Nitrogen cycle is given in the following figure:







































Summary of various N-fixing bacteria:

Azotobacter, Thiobacillus, Mycobacterium etc. : Free living & aerobic.

Closteridium Klebsiella : Free living & anaerobic.

Rhizobium, Aopzprirllium Frankia : Symbiotic & anaerobic

Citrobacter : Symbiotic and anaerobic

Bacteria & Antibiotics: Though first antibiotic penicillin was obtained from ascomycetes fungus Penicillium notatum by Alexander Flemming in 1929, yet soil-borne bacteria Streptomyces of actinomycetes (ray fungi) are rich source of various types of antibioitics. Antibiotics are chemical inhibition. The term 'antibiotic' was coined by Salman Waksman. Antibiotics are known as chemotherapeutic agents. Some of the antibiotics extracted from bacteria are bacitracin, subtilin, polymyxin, gramicidin etc.



Salient features of some antibiotics chemotherapeutic agents



Name of the antibiotics

Name of the discover

Source of antibiotics

Action of antibiotics

Penicillin

Alexander Flemming

P. notatum

P. chrysogenum

Breaks muco complex cell wall of bacteria.

Streptomycin

Waksman

Streptomyces griesus

Inhibits synthesis of 30S fragment of ribosome in bacteria.

Erythromycin

Mc Guire

S. erythreus

Inhibits synthesis of 50S fragment of ribosome in bacteria

Chloromycin

Burkholder

S. venezualae

Inhibits initiation of protein synthesis in bacteria.

Aureomycin

Duggar

S. auerofaciens

Inhibits formation of tRNA amino acid complex.

Terramycin

Pfizer Ltd.

S. rimosus

Inhibits formation of tRNA amino acid complex.



Penicillin is not broad spectrum antibiotic because it is more active on gram positive bacteria, less effective on gram negative bacteria. Streptomycin is first brad spectrum antibiotic which is equally active on gram positive and gram negative bacteria both.

Bacteria & Miscellaneous uses

(a)Aerobacter aerogenes decomposes DDT whereas Flavobacterium and Corynebacterium decompose 2, 4-D etc. DDT and 2, 4-D are non-biodegradable chemicals, which may be lethal even.

(b)Bacillus pudita, pseudomonas and some other oil-eating bacteria help in cleaning up oil spills. They thus help in preventing water pollution of seas/oceans caused due to oil refineries.

(c)Anand Mohan Chakroborty has developed genetically engineered bacteria named Superbug that feeds on oil spills.

(d)Bacterium Methylophylus methylotropous is source of single cell protein (SCP) the product was called 'Pruteen'. Fungus Fusarium is also used for the purpose i.e. preparation of mycoprotein on larger scale.

(e)Batch culture & continuous culture are two main methods of fermentation on larger scale. The former is closed system whereas latter is open system.







3e) Bacteria: Classification:

Bacteria and blue green algae are prokaryotes as they lack true nucleus in absence of nuclear membranes. They were placed together under Schizophyta by Cohn in 1853. However, Whittaker in his famous five kingdom classification placed prokaryotes under Monera, a term coined by Stanier. Bergey's Manual in Determinative Microbiology (1974) is widely recognized in medical science:































3f) Bacteria: Structure of a Cell:

i.Bacteria is placed in plant kingdom because contains rigid & non-living cell wall which is outer most in position. Bacterial cell wall is made up of muco-complex or peptidoglycan. Muco-complex is a complex formed between few simple sugars and proteins: The sugars are N-Acetyl glycosamine (NAG) and N-Acetyl Muramic Acid (NAM) or murein. Protein of mucocomplex are formed by few amino acid i.e. Glycine, Lysine, glutamic acid and diaminopimelic acid (DAP): Peptidoglycan linkage of bacterial cell wall is broken by lysozyme enzyme of bacteriophages or by antibiotic penicillin.

Staining of bacterial cell wall was first introduced by Christian Gram. It involves staining of bacterial cell with crystal-violet (Gram Stan). With this bacterial cells appear deep violet coloured. Crystal violet staining is followed by treatment with organic solvent. If deep violet colour is retained by bacterial cell after treating with organic solvent then bacteria are called Gram positive. If deep violet colour is lost after treating with organic solvent then bacteria are termed as Gram negative.

Difference between Gram Positive and Gram Negative Bacteria

Mucocomplex content is high in gram positive bacteria

Mucocomplex content is low in gram negative bacteria

Teichoic acid is present

Teichoic acid is absent

Penicillin is more effective

penicillin is less effective

Lipid content is low, this explains why deep violet colour is retained after treatment with organic solvent

Lipid content is high, this explains why deep violet colour is lost after treatment with organic solvent lipid is dissolved in organic solvent

Example: Bacillus subtilis (Haybacillus)

Example: E. coli

Mucocomplex cell wall is surrounded by slime layer, which changes into capsule layer during unfavourable condition. Capsulated stage in bacteria is resistant to antibiotics to larger extent.

ii.True nucleus is absent in bacteria because nuclear membrances are absent in prokaryotes, Incipient nucleus in prokaryotes is called 'NUCLEOID' and it is represented by a double stranded circular DNA only. Nucleolus is also absent. ds circular DNA without proteins in bacteria may also be considered as bacterial chromosome.

iii.Membranou cell-organelles remain absent in prokaryotes including bacteria, however in some bacteria, inward folding of cell membrane may form structures like mesomomes & chromatophores: Mesosomes, first reported by Frtiz-James, develop in aerobic bacteria for complete breakdown of macromolecules in presence of O2. Definite role of mesosomes is also reported during replication of DNA. Chromatophores or photosynthetic lamellae develop for photosynthesis. Ribosomes for protein synthesis are 70S in size and they remain embedded directly in cytoplasm in absence of ER. Since ribosomes remain embedded directly in cytoplasm this explains why density of prokaryotic cytoplasm is more than density if eukaryotic. The two fragments of 70S ribosomes are 50S & 30S.

Carbohydrates are stored in the form of glycogen whereas storage of protein is in the form of volutin granules. Storage of inorganic substances is in the form of granulose.

iv.A bacterial cell may or may not have flagella. Bacterial flagellum is different from eukaryotic flagellum because bacterial flagellum is made of flagellin proteins and 9+2 arrangement is also not present. Flagella like structures but much smaller in length are called fimbrae or Pilli. Fimbrae or pili may be specialized to form sex pili, which play significant role during conjugation in bacteria.

v.Extra inheritable material, present in cytoplasm bacterial cell is called 'plasmid' discovered by Lederberg. Some plasmids are capable of combining with main genetic material i.e. DNA of bacterial cells. They are called Episomes. Therefore, it may be concluded that all episomes are plasmids but all plasmids are not episomes. R Factor in bacteria is purely a plasmid; it provides resistance against antibiotic. The other examples of common plasmids in bacteria are pBR322 and Col-factor, which produces colicin. F factor (fertility-factor) in bacteria is an example of episome. It plays significant role in conjugation. Bacterial cell, which contains F factor, is cytoplasm called F+ cell or donor cell and bacterial cell, which lack F factor, is called F– cell or recipient cell. Bacterial cell is termed as High frequency Recombinant (HFR) when F factor combines with DNA of bacteria.

3g) Bacteria: Reproduction:

i.Asexual reproduction through binary fission is very common method of reproduction in Bacteria. It takes place during favourable conditions. One parent bacterial cell splits to form two daughter bacterial cells in binary fission.

A bacterial cell divides every minute; time required to form 128 cells of bacteria will be? Number of divisions required to form 128 bacterial of cells will be:

1 Cell ---- Istdiv-----2 Cells ----IInddiv----4 Cells ----IIIrddiv---8 Cells---IVthdiv---16 Cells---Vthdiv---32 Cells----VIthdiv-----64 Cells---VIIthdiv---128 cells. Thus, numbe of divisions required to form 128 bacterial cells=7. Therefore, time required to form 128 bacterial cells: 7 divisions X 1 minute = 7 minutes.

A bacterial cell divides every minute it takes one hour to fill a cup; time required to fill half & quarter of the cup will be?











From the above, it is clear that: (X + 1+ 1) + 60. Hence, X = 58 minute.

Therefore time required to fill ¼ cup will be: 58 minutes and time required to form ½ cup will be 58 + 1 = 59 minutes.

ii.Conidia like structure develops during asexual reproduction in fungi like bacteria i.e., in Actinomycetales.

iii.Bacteria forms endospore during unfavourable conditions it is the hardest structure of bacteria. Bacterial cell under goes capsulated stage and entire inner contents shrink to form endospore. One bacterial cell forms one endospore during unfavourable conditions.

iv.Sexual reproduction or syngamy involves fusion of two haploid units or gametes. The two haploid units are formed after meiosis or reduction division. In bacteria meiosis or reduction division is not possible because bacterial cell contains single chromosome. This sexual reproduction or syngamy is not reported in bacteria in absence of meiosis. Sexual reproduction plays significant role in evolution because it is main method of genetic recombination in living entities. Though well-defined sexual reproduction is missing in bacteria, yet bacteria shows some important methods of genetic recombination.

3h) Bacteria: Methods of Genetic Recombination:

Three main methods of genetic recombination are reported in bacteria. They are conjugation, transformation and transduction. In addition to these three, sexduction is also a method of genetic recombination in bacteria.

i.Conjugation, a method of genetic recombination in bacteria was first reported by Lederberg & Tatum in bacterium E. coli. It involves transfer of 'F factor' from donor bacterial cell F+ to recipient bacterial cell F– through direct contact. The two types of bacterial cells i.e. F+ and F– come in contact with each other through sex pili and a passage called conjugation tube develops for transfer of F factor. F factor is doubled before transfer and F– cell becomes F+ after transfer of F factor. Thus genetic recombination takes places in recipient cell:





















ii.Transformation another method of genetic recombination in bacteria was first reported by Griffith in 1926-27 in bacterium Diplococcus pneumonae. The event is in vitro (in Lab) only and not in vivo (not in nature). It involves transfer of a part of DNA of donor bacterial cell to recipient bacterial cell through medium solution. Part of DNA of donor bacterial cell, which is transferred, is called transformosome. It is 1/1000 of original DNA content of donor bacterial cell.























Griffith prepared two strains of Diplococcus pneumonae i.e. non-capsulated, non-virulent type (R-Type) and capsulated, virulent type (S-Type). The two types were infected in mice and following observations were observed:

R-Type : all mice healthy

S-type : all mice died of pneumonia

S-type Heat killed : all mice healthy

R-type + S-type (heat killed) : all mice died of pneumonia

The observation that all mice died when R-type + S-type (heat killed) was injected, prompted Griffith to conclude that there was transfer of 'something' from heat killed S-type to R-type, which made R-type virulent. Griffith could not identify this something all that time. Avery, Macleod & McCarty (Avery et al) later on repeated the experiment of Griffith in 1948 and identified that this something was part of DNA of S-type (heat killed), which was transferred to R-type. These parts of DNA called transformosome made R-type virulent. Avery et al. with this finding established the status of DNA as every genetic material. Work of Hershey & Chase involving DNA as infective part of Bacteriophage is another experiment, which establishes status of DNA as genetic material.

iii.Transduction yet another method of genetic recombination, was discovered by Zinder & Laederberg in bacterium Salmonella typhi. It involves transfer of a part of DNA (from donor bacterial ell to recipient bacterial cell through bacteriophages. The part of DNA transferred is about 1/1000 of original DNA content. The event is rare but it is reported in nature. New phages may carry a part of DNA of bacterial cell. Bacterial cell B' (recipient cell) receives a part of DNA of Bacterial cell A' (donor cell) through bacteriophages. In generalised transduction, recipient cell receives plasmid of donor cell.



























iv.SEXDUCTION was reported by Addelburg & Burns in E. coli. They observed that during conversion of HFR into F+ dissociation of F factor is not always accurate. F factor some times carries a part of main DNA of Bacteria. This F factor with a part of bacterial DNA is called F prime of F' factor. When this cell conjugates and transfers the gene attached with F prime, recipient cell becomes 'partially diploid' for the particular gene. This phenomenon has been described as sexduction in bactera.



Methods of genetic recombination in bacteria are tools of genetic engineering that is a nascent branch of biotechnology genetic engineering aims at developing superior character of desired results by manipulating at gene level. Bacterial plasmids like pBR322, Ti factor (Tumor inducing factor) etc are of immense value in genetic engineering. Several diseases like Diabetes etc may be cured with the help of genetic engineering. High yielding & disease resistant varieties of crops may also be developed with the help of genetic engineering. Thus genetic engineering in near future may prove boon to mankind: but at the same time it may prove to be a curse as well. The biggest threat of genetic engineering is of biological warfare. Pathogens of several dreaded diseases of past may be regenerated again which may cause huge destruction to mankind.



4. Microbiology: Miscellaneous

i.Mycoplasma were discovered by Nocard & Roux as Mollicutes. They are 'L-form' of bacteria, which are filterable like viruses. They are called 'L-form' because they lack well defined mucocomplex cell wall of typical bacteria. Due to this they are polymorphic entities i.e. they may exist in several forms; hence the popular name of 'joker' in biological kingdom. Due to absence of cell wall, mycoplasma looks like a boiled fried egg. Mycro Plasma are gram negative and are not affected by antibiotics penicillin (inhibitor of cell wall formation) but are inhibited by tetracyclin Mycoplasma has a definite cellular organization; a cell of mycoplasma is the smallest cell. Genetic material is ds DNA that is highly coiled and attached with a disc at one end. Cytoplasm contains RNA & 70S ribosomes. Mycoplasma require sterols for the growth. Some biologists place mycoplasma between viruses & bacteria. Dieseases like 'Little leaf of brinjal' and 'witches broom' of sugarcane etc are caused by Mycoplasma and related mollicutes placed under Pleuro Pneumonia like organism (PPLO). Some microbiologists have named mycoplasma like organism as Spiroplasma, which cause diseases on plants.

ii.Rickettsias are tiny obligate, gram negative pleomorphic but walled parasites present in blood sucking insects like ticks, lices, mites etc. They may be rod-shaped or spherical. They have mucopeptide cell wall and genetic material is ds circular DNA. Cytoplasm contains RNA and 70S ribosomes. They are sensitive to antibiotics and multiply by fission. Diseases like Typhus, Q-fever, Trench fever rocky-mountain spotted fever etc are caused by Rickettsias. Ricketts first observed them but Proper description was made by Rocha-levis later on.

iii.Spirochaetes are protozoa like aflagellate bacteria. They have an axial filament called crista, which is spirally coiled. They show gliding movement and multiply by fission. Diseases like Syphilis, Jaundice etc are caused by them.

iv.Chlamydiae: They are Gram(-ve) intracellular parasites of about 0.25 m. size, often grouped along rickettsiae. However, their reproductive cycle differs from rickettsiae in the formation of initial or reticulate bodies (RB) and elementary bodies inside host phagosome. They have cell wall similar to typical bacterial wall. They lack ATP formation and obtain the same from outside chlamydiae are thus energy parasites. The common diseases caused by chlamydiae include Conjuntivitis, nongonococcal urethritis and lymphogram losa venecatum, pneumonia and bronchopneumonia, psittacosis.



SARS (Severe Acute Respiratory Syndrome), this viral disease was first reported in Guangdong Province in Southern China in Nov. 2002. The cause of SARS was identified as a member of the Corona Viridae (single stranded RNA viruses).

SARS causing virus transmitted by droplets from coughs and sneezes.

It produces severe form of pneumonia, fever of 100.4 oF (some time with chills), headache, bodyaches and malaise.

High Security Animal Disease laboratory Bhopal, is the main center where SARS virus study carried out.





Vaccination:

Vaccination is a preventative strategy that aims to stimulate the host immune system, by exposing it to the infectious agent in question in an inactivated or incomplete form. There are four types of virus vaccines:

1. Attenuated (='weakened') vaccines contains 'live' viruses, but ones whose pathogenicity has been greatly reduced. E.g. Polio Virus vaccine developed by Albert Sabin in the 1960s. The cowpox virus used by Edward Jenner in his pioneering vaccination work in the late 18th century was a naturally occurring attenuated version of the smallpox virus.

2. Inactivated vaccines contain viruses which have been exposed to a denaturing agent such as formalin. This has the effect of rendering them non-infectious, while at the same time retaining their ability to stimulate an immune response. Vaccines directed against influenza are of this type.

3. Subunit vaccines depend on the stimulation of an immune response by just a part of the virus. Since the complete virus is not introduced, there is no change of infection, so vaccines of this type have the attraction of being very safe. Subunit vaccines are often made using recombinant DNA technology; the first example to be approved for human use was the hepatitis B vaccine, which consists of part of the protein coat of the virus produced in specially engineered yeast cells.

4. DNA vaccines are also the product of modern molecular biology techniques. DNA coding for virus antigens is directly injected into the host, where it is expressed and triggers a response by the immune system. Vaccines of this type have not so far been approved for use in humans.





Satellite Viruses:-

i.Satellite viruses are also known as 'incomplete viruses'.

ii.The replication of this virus is dependent of coinfection of a second 'helper' virus.

iii.Satellite virus and helper virus are separate entities; they encode their own capsids and infect the cell independently.