Summary The Most Important Notes on General Microbiology and Immunology
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Course
Medical Microbiology
Institution
Medical School
In this capsule between your hands, we have done hard and precise work to summarise the most important notes on general microbiology and immunology (for undergraduate medical students). We hope you all guys find this capsule helpful. - - - - This capsule consists of 18 pages.
General Microbiology
Prokaryotes have no Nucleus, no nuclear membrane, No Mitochondria, have 70S Ribosomes,
have No sterol in cytoplasmic membrane (Except Mycoplasma), Prokaryotes = Bacteria and Blue
green algae.
Eukaryotes have True nucleus, Nuclear-membrane, Mitochondria, 80S Ribosomes, have sterol in
cytoplasmic membrane, Eukaryotes includes Human and animal and plant and Fungi and algae.
Viroids are only RNA which causes plant diseases – Prions are only proteins.
Bacteria has one chromosome (Nucleoid) which is essential for Life.
Plasmids are extrachromosomal circular DNA, not essential (dispensable), carry extra
information.
Ribosomes of bacteria are 70S (50S + 30S), consist of protein and RNA site of protein synthesis.
Inclusion granules are storage sites of nutrients and energy Volutin granules are
metachromatic.
Mesosomes are invaginations of cytoplasmic membrane site of respiration (alternative for
mitochondria) and are involved in cell division.
Cytoplasmic membrane of bacteria phospholipid bilayer selective permeability + Excretion
of enzymes + Respiration (Mesosomes) + Cell wall synthesis + Reproduction (Mesosomes) +
Chemotaxis.
Cytoplasmic membrane Resynthesize cell wall of bacteria.
Cell wall of bacteria is formed of peptidoglycan Protection + Shape + Division + Staining
affinity.
Gram positive cell wall Thick PG + Teichoic acid
Gram negative cell wall Thin PG + Periplasm + Outer membrane (LPS).
Outer membrane of Gram negative LPS Lipid A (Endotoxin) + O Saccharide (antigen)
Endotoxin Part of gram-negative cell wall (Lipid A) Causes Septic Shock.
Mycoplasma is the only bacteria that exist naturally without cell wall No shape – Not affected
by penicillin + Not stained with Gram stain.
L-Forms Cell wall defective bacteria due to exposure to lysozyme or penicillin can
resynthesize cell wall – Causes relapses of infections.
Capsule extracellular layer that adhere to surface of the bacterium Polysaccharide (except B.
anthracis = Polypeptide) Appear as halo when stained with gram Protect bacteria from
phagocytosis + Used for adherence.
Slime layer Loosely distributed layer
Glycocalyx Meshwork of polysaccharide fibrils (Form biofilms) Strept mutans Dental caries.
Flagella Organ of motility Protein Seen by EM Antigenic (H antigen).
Monotrichous (One flagellum) – Peritrichous (flagella around bacterium) – Lophotrichous
(Multiple polar flagellae) – Amphitrichous (Flagella at both poles).
Axial filaments Endoflagella Spirochetes.
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, Pili = Fimbria Proteins Adherence (Fimbriae) / Conjugation (Sex pili).
Endospores Highly resistant structure formed by bacteria in response to unfavorable conditions
Dormant (No reproduction or metabolism) formed by Two bacteria Bacillus + Clostridium.
Spores are resistant because of thermal resistance, presence of Dipicolinic acid, impermeability,
low water content and Low metabolism.
Germination (Return of spores to vegetative state) occurs within 15 minutes when environment
becomes suitable for growth.
Bacterial Growth = Binary fission = increase in number (starts with slight size increase).
Generation Time = Doubling time time taken by bacteria to double in number = Time between
2 successive divisions 13 minutes in V. cholera / 24 hours in M. tuberculosis.
Autotrophs Bacteria which synthesize organic compounds (Glucose) from inorganic compounds
(CO2 and ammonium salts).
Heterotrophs Bacteria which Cannot synthesize organic compounds.
Obligate (Strict) aerobes Require oxygen for growth.
Obligate anaerobes Require absence of oxygen for growth.
Facultative anaerobes prefer oxygen but grow in its absence (Grow better in oxygen presence)
Aerotolerant bacteria prefer absence of oxygen but grow in its presence (prefer anaerobic)
Microaerophilic Require reduced oxygen level.
Aerobic respiration Oxygen is the final electron acceptor.
Anaerobic respiration Nitrate or sulfur is the final electron acceptor.
Oxygen Use Toxic compounds (Superoxide – Hydrogen peroxide) aerobic bacteria have
Enzymes which detoxify these molecules Superoxide dismutase and catalase.
Capnophilic bacteria Require higher concentration of CO2 Neisseria / Brucella.
Mesophilic bacteria grow in temperature range of 20-40° C
Psychrophilic bacteria grow in temperature range of 0-8° C
Thermophilic bacteria grow in temperature range of >60° C
Bacteriophage Viruses that parasitize bacteria composed of Head (protect the nucleic acid)
and Tail (inject nucleic acid inside bacterial cell).
Lytic (Vegetative) cycle Virulent Phage Phage destroy bacteria (Lytic) then released
Generalized transduction (May take random DNA fragments and transfer it to another bacterium.
Lysogenic (Temperate) Cycle Temperate phage phage genome is integrated with bacteria
chromosome Prophage bacteria is called lysogenic bacteria Specialized transduction
(when phage is excised it takes part of bacterial DNA which is adjacent to it and transfer it to
another bacterial cell).
Uses of bacteriophages Cloning vectors – Phage typing – Research.
Gene segment of DNA carries information for specific property.
The only essential DNA for bacteria is the chromosome.
Plasmids can replicate independently of the bacterial chromosome.
Functions of plasmids Sex pilus formation (Conjugative plasmid / F Plasmid) – Antibiotic
resistance (R Plasmid) – Virulence plasmids (Toxin, Adhesins) – Bacteriocin production.
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, Bacteriocin Substance produced by certain bacteria against another strain of bacteria.
F Plasmid = Sex pilus = Conjugation
R Plasmid = Antibiotic resistance.
Transposable genetic elements DNA segments that can insert themselves in other DNA
molecules (Jumping genes)
Phenotypic variation change in bacterial characters in response to environmental changes
Reversible Not heritable L-Forms / Loss of flagella after phenol exposure
Genotypic variations Change in bacterial characters due to change in genetics irreversible
heritable Mutation / Gene transfer (Transformation – conjugation – Transduction).
Mutation Change in the nucleotide sequence of DNA (spontaneous or induced).
Transformation Uptake of Free naked DNA (from dead bacteria) depends on competence
(ability of bacteria to take up DNA).
Transduction transfer of DNA from one cell to another by means of a bacteriophage.
Generalized transduction Lytic cycle Virulent phage Random DNA
Specialized transduction Lysogenic cycle Temperate phage Special part of DNA
Conjugation Transfer of DNA after cell to cell contact the most frequent mechanism for gene
transfer requires Sex pilus (F Plasmid).
Antibiotic antimicrobial produced by microorganism (synthetic if made synthetically /
semisynthetic if modified).
Chemotherapeutic agent synthesized antimicrobial agent.
Bacteriostatic agent inhibit growth bacteria multiply again after removal of drug
Bactericidal agent Kill bacteria Bacteria cannot multiply again
Selective toxicity ability of antimicrobial to harm pathogen without harming host.
Spectrum of activity range of microorganisms affected by antibiotics.
Broad spectrum wide range of Gram positive and negative
Narrow spectrum gram positive of negative.
Limited spectrum drug against single organism.
Mechanisms of antimicrobials cell wall synthesis inhibition – cell membrane function inhibition
– protein synthesis inhibition – Nucleic acid inhibition.
Drugs which inhibit cell wall synthesis B Gly Cy Beta lactams (penicillin – cephalosporins) –
Glycopeptides (Vancomycin – Teicoplanin) – Cycloserine and bacitracin.
Beta lactams inhibit last steps for PG synthesis while Glycopeptides and cycloserine inhibit early
steps.
Drugs against cell membrane I Can Play Antibacterial (Polymyxin – Colistin) – Antifungal
(Amphotericin – Nystatin – imidazole).
Anti-Cell membrane drugs are highly Toxin due to similarities between human and bacterial
membranes.
Drugs against 30S subunit (inhibit protein synthesis) TEAM Tetracycline + Aminoglycosides
(Gentamycin – Streptomycin – amikacin).
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