General Microbiology

Scientists

Louis Pasteur

Mnemonic: FATHER CAR

Developed vaccines for:

Cholera.
Anthrax.
Rabies.

Louis → Liquid (Liquid media)

Vaccine CAR (coined vaccine, Germ cell theory) → Autoclave

Pasteurisation → Fermentation

Father of modern microbiology.

Founded Pasteur Institute in Paris.

Developed Pasteurisation (for milk).

Key contributions:

Liquid media.
Fermentation Principle.
Autoclave.
Disapproved Theory of abiogenesis.
Proposed Germ cell Theory.
Coined the term "vaccine"

Robert Koch

Father of modern microbiology.

Significant contributions:

Mnemonic:

Koch organisms (koch bacilli - tb, cholera organism)
are solid (solid culture media) → hang (hanging drop motility) → apply paint (aniline dye)

Koch postulates.

Discovery of Koch Bacilli (Tuberculosis).

Identification of Cholera organism.

Development of Solid culture media.

Application of Aniline dye colour.

Introduction of Hanging drop motility.

Koch Postulates

Old (4) Postulates:

Constant association of causative organisms with disease.

Isolation in culture media is possible.

Culture growth inoculated in animals should produce the same lesion.

Re-isolation from the experimental animals is possible.

New (1) Postulate:

Humans should produce antibodies in serum whenever there is an infection (antigen).

Exceptions from Postulates:

Mycobacterium leprae.
Treponema Pallidum.
N. Gonorrhoea.
My pallu gone

Paul Ehrlich

Identified the Ehrlichia organism.

Father of chemotherapy.

Developed Toxin-antitoxin standardisation.

Developed the Acid-fast stain/Ziehl Neelsen stain.

Other Scientists

Walter Reed

Worked on yellow fever
Identified Aedes mosquito as vector
Walter → Water → aedes → yellow fever

Joseph Lister:

Father of Antiseptic surgery.
Used carbolic acid.

Anton Von Leeuwenhoek:

Father of the Light microscope (unilocular)
First to observe "little animalcules"

Ernst Ruska:

Invented the Electron microscope

Edward Jenner:

Developed the first vaccine for smallpox.
Coined the term "vaccination"
Wardil (Edward) kidakkunna small (smallpox) kidsnu vaccination () cheyynm

Karry B Mullis:

Developed PCR.
KBM PCR 3 letters

H C Gram:

Developed Gram staining.

Kleinberger:

Discovered L forms (cell wall deficient forms).
K- L

Alexander Fleming:

Discovered Penicillin.

Barbara McClintock:

Discovered Transposons (Jumping genes)
Tick tok - Jumping genes

Nobel Prizes During Covid Era

HCYV mechanism:

Michael Houghton
Harvey J. Alter
Charles M. Rice

CRISPR Cas9:

Nobel Prize

Emmanuelle Charpentier
Jennifer A. Doudna.
For repurposing the CRISPR CAS enzyme system for gene editing.
Using HDR → gene knock-in.

Actually uses Non HDR → Gene knock out by default

The CAS enzyme makes double-stranded DNA nicks.
Nicks occur at sites complementary to its guide RNA.

NOTE: Nobel Prize 2025

Awarded to Dr Mary E. Brunkow, Dr Fred Ramsdell, Dr Shimon Sakaguchi
Discoveries in peripheral immune tolerance
Identification and characterization of regulatory T cells (Tregs)

Differential Stains

1. Gram Stain (+/-)

Procedure steps:

Crystal Violet (primary stain).
Iodine (mordant).
Alcohol/Acetone (decoloriser).
Safranin (secondary stain).
Come in and stain
VISA

Results:

Type	Color
Gram-positive	Purple
Gram-negative	Pinkish red

Organisms that stain poorly:

MRCS
Mycobacterium.
Rickettsia.
Chlamydia.
Spirochetes.

2. Acid-Fast Stain (Ziehl Neelsen Stain)

Procedure: Application of

Carbolfuchsin (primary stain).
heat (mordant).
Acid Alcohol (decoloriser).
Methylene Blue (counter stain).
Acid CHAMBi

H2SO4 Concentration for Decolourisation:

Organism	H2SO4 Concentration
TB	• 20–25%
Lepra, Cryptosporidium, Isospora	• 5% (Fite Faraco stain) • Five and fite faraco
Nocardia, Legionella	• 1% (Modified ZN stain)
Spores, Head of sperm	• 0.25–0.5% • S-5

Acid-Fast Organisms:

Mycobacteria.
Nocardia, Legionella.
Isospora, Sperm.
Cyclospora, Cryptosporidium.
Hooklet of hydatid, Taenia saginata egg.

Cold Ziehl Neelsen Stain:

No heating (Kinyoun/Gabbet stain).

Used for Coccidian parasites.

Mordant involves increased concentration of phenol.

Cold - kinyon - coccidian parasite

3. Albert Stain

Used for C. diphtheria.

Albert stain (Mnemonic: TIM):

Albert 1:

Malachite green (stains organism)
Toluidine blue (stains Volutin granules)
glacial acetic acid.

Albert 2:

Iodine.

Albert ()is volatile(), bipolar(), has many colors().

Always() put() a nyc() laugh()

Other stains

Always () put() a nyc() laugh()

Albert stain.
Ponder's stain.
Neisser stain.
Loeffler methylene blue (best stain).

Microscopy

2 swabs from beneath pseudomembrane
Cells show Chinese letter/Cuneiform appearance (V-shaped and L-shaped)

due to snapping division.

Presence of Volutin granules / Babes Ernst granules / Bipolar granules/
Metachromatic granules

polymetaphosphate energy stores

4. Miscellaneous Stains

Spore stains:

For resting/dormant form of bacteria.

Stains used:

ZN stain (0.25-0.5% H2SO4).
Schaeffer and Fulton stain/Modified Ashby stain:

Malachite green for spore.
Safranin Red for organism.
Shaffy fully (Schaeffer and Fulton) modified aayi (Modified Ashby)
muslim (Malachite green. Pacha vithu - spores) to hindu (Sangi red)

Negative stain:

Stains the background.

Used for Cryptococcus.

Examples:

Indian Ink.
Nigrosin.

Silver stains:

Produce a black colour.

Used for Flagella and Spirochetes.

Examples:

Fontana stain.
Levaditi's stain.
Silver pirates live (Levaditi's) near fountain (Fontana)

Flagella Stain

Leifson and ryu’s stain

Mordant → Tannic acid
leave son and rho and get tanned

Microscopes

1. Light Microscope

Light source: Transmitted light.

Lenses:

Eyepiece lens (10X).
Objective lens

Scanner 4X
Low 10X
High power 40X
Oil immersion 100X

Total magnification:

Eyepiece x objective.

Maximum magnification:

1000X.

Resolving power of microscope

Depends on

Aperture of objective and condensor
Wavelength of light

Dont depend on

Thickness of film
Focal length of eyepiece → Affect magnification

2. Dark Field Microscope

Light source: Reflected light (By changing Condensor)

Used for thin structures:

Flagella.
Spirochetes.

3. Interference Contrast Microscope

Reveals cell organelles.

Allows measurements of cell chemical constituents:

Lipids.
Protein.
Nucleic acid.

4. Fluorescence Microscope

Source of light: Ultraviolet light.

Mirror: Dichroic mirror.

Principle: Converts shorter wavelength light to longer wavelength light.

Dyes:

Microorganism	Dye	ㅤ
TB	Auramine and Rhodamine	ㅤ
Malaria	Acridine Orange.	Malam orange from anus
Fungus	Calcofluor White.	floor il fungus
Flow Cytometry	FITC (Fluoro isothiocyanate).	fit and flow

Autofluorescence

Cyclospora
Isospora
Formalin
NADPH

Autofluorescence cycle () is () for () nadiya ()

Microscope	Light
Light	Transmitted Light
Dark Field	Reflected Light
Flurescent	UV Light
Electron Microscope	No Light, Beam of electrons
Phase Contrast	Difference in refractive indices

5. Phase Contrast Microscope

Use: To view internal details of living cells.

Principle: Differences in refractive indices shown in different phases.

Parts:

Annular diaphragm.
Annular phase plate.

Note: Hairy cells in hairy cell leukaemia are seen on it.

6. Electron Microscope

Inventor: Ernst Ruska.

Source: A beam of electrons.

No light is used.

Medium: Vacuum.

Resolution

Electron → 0.2 nm

Light → 0.2 Um

Types of electron microscope

Bacterial Anatomy

1. Capsule

Capsule: Tough and demarcated.

Slime layer: Loose.

Streptococcus salivaris has both.

Capsulated Organisms:

Anthrayile (Bacillus Anthracis) strip(Streptococcus Pneumonia) club(Klebsiella Pneumoniae) ile staph (Staphylococcus Aureus) yersiniyakk (Yersinia Pestis) bore (Bordetella Pertussis) adich. vibe (Vibrio Parahaemolyticus) men (meningococcus) nu Hi (Hemophilus Influenza) paranju. perforate (Clostridium Perfringens) cheythappo cry (Cryptococcus) (fungus) cheythu nyceayitt (Neisseria)

Composition:

All capsules are polysaccharides.

Except:

Yersinia pestis - F1 peptide.

Years kazhinjal Fade

Bacillus anthracis - polypeptide

Anthrakkaru Protein

S. aureus has a microcapsule.

2. Cell Wall

Gram-positive:

Composition: Peptidoglycans++.

Thick Peptidoglycans.

Pentapeptide cross bridge.

Teichoic acid.

Lipid content: 15-50%.

PPPT( Positive Peptidoglycans, Pentapeptide Teichoic acid)

Gram-negative:

Thin Peptidoglycans → get washed out

Outer membrane has

Porins
Endotoxins /Lipopolysaccharide++

Composition: OPA

O- antigen
P- Polysaccharide
A- lipid A

Periplasmic space

has endoflagella → feature of spirochetes

Endotoxin

Source: LPS in outer membrane of gram -ve bacteria

All gram negative have endotoxin

Also Listeria (gram +ve)

OPA → Endotoxin

O antigen
Polysaccharide.
Lipid A (most imp)

Linulus amebocyte assay (LAL)

Clinical Effects

Fever, shock, hypotension, DIC

No toxoids, no vaccines

Induces TNF, IL-1, and IL-6

Causes Meningococcemia

Feature	Exotoxins	Endotoxins
Source	Both G +ve and -ve	outer cell membrane of gram -ve + Listeria (G +ve)`
Secreted from Cell	Yes	No
Antigenicity	high	Poor
Vaccines	Toxoids used as vaccines	No toxoids, no vaccines
Chemistry	Polypeptide	Lipid A of LPS
Toxicity	High	Low
Mode of Action	ㅤ	Induces TNF, IL-1, and IL-6
Heat Stability	Destroyed rapidly at 60°C Except ↳ staphylococcal enterotoxin ↳ E coli heat-stable toxin ↳ B cereus emetic toxin	Heat stable ↳ Stable at 100°C for 1 hr
Typical Diseases	Tetanus, botulism, diphtheria, cholera	Meningococcemia

Exotoxins

Clostridium tetani

Toxin: Tetanospasmin
Protease → cleaves SNARE
⛔ GABA and glycine release from Renshaw cells in spinal cord
Spastic Paralysis (Lockjaw/Trismus)

Note: Botulinum toxin

Superantigens Causing Shock

Polyclonal activation of T cells

Activate T cell directly → Cause shock and MOF

MOA: [Cross-links β region of TCR to MHC class II on APCs]

Antigen bind to MHC II → outside antigen binding site
↑↑ release of IL-1, IL-2, IFN-γ, and TNF-α → shock

Bacterium	Toxin (Superantigen)	Clinical Syndromes
Staphylococcus aureus	Enterotoxin F ↳ TSST-1	• Toxic shock syndrome ↳ (fever, rash, shock) D/t • Retained tampon • Retained nasal guaze piece
Streptococcus pyogenes	Pyrogenic exotoxin (SPE)	• Scarlet fever-like syndrome ↳ (fever, rash, shock), • Scarlet fever

TOXINS CODED BY LYSOGENIC PHAGE:

Mnemonic: A-B-C-D-E

A - GABS: A and C toxins of S. pyogenes

AC- pus

B - C and D toxins of Botulinum

CD - Boat

C - Cholera toxin
D - Diphtheria toxin
E - Enterohemorrhagic E. coli (EHEC) - Shiga-like toxin/verocytotoxin

3. Cell Membrane

Invagination forms Mesosomes/Chondroids.

Act as the respiratory unit in bacteria.

Prominent in gram-positive bacteria.

4. Ribosomes

70S.

5. Nucleus

Single circular.

Double-stranded DNA.

6. Flagella

Consist of 3 parts.

Use: Locomotion.

Flagella antigen: H antigen.

Types based on location:

Flagellar Arrangement	Description	Examples
Monotrichous	• One flagellum on one side	• Vibrio, • Pseudomonas • VONE, Mono
Amphitrichous	• Flagella on both sides • Apparom Ipparom	ㅤ
Lophotrichous	• Tuft of flagella on one side • Loop on one side	• Helicobacter
Peritrichous	• Flagella distributed all around	• Proteus • E. coli • Listeria

Flagellar stain

Leifson and ryu’s stain

Mordant → Tannic acid
leave son and rho and get tanned

Widal test:

Antigen	Location	aka	Note
O antigen	Cell wall	Somatic Ag	Same for all
H antigen	Flagella	Flagella Ag	Different

Types of motility:

Type of Motility	Examples	ㅤ
Tumbling	• Listeria	ㅤ
Darting-like	• Vibrio, • Campylobacter	Vibe camp il dart throwing
Corkscrew	• Treponema	Pallilu Screw
Lashing	• Borrelia	Borring eye lashes
Twitching	• Eikenella, • Trichomonas vaginalis	Vaginayil ikkilakkiyappo twitch cheyth
Falling leaf	• Giardia lamblia ↳ (STRING TEST)	Girtha huva leaf
Differential motility	• Motile at 22–25°C, • non-motile at 37°C ↳ (Yersinia, Listeria)	Yes different list
Swarming	• Proteus. • Vibrio parahemolyticus • Bacillus Cereus. • Serratia. • Clostridium tetani	principal vibe sir sir clos teacher

7. Fimbriae/Pili

Hairlike structures.

Use: Adhesion.

Detection:

Hemagglutination.
Surface pellicle test.

Note: Type IV pili

In Neisseria and Pseudomonas
Used for locomotion.

Pili(Type IV pili) pseudo(Pseudomonas ) nyc(Neisseria ) aayi move() cheyth

Bacterial Physiology

Oxygen and Carbon Dioxide Requirements

Aerobic: Need O2.

Anaerobic: No O2 needed.

Capnophilic: Require CO2

Campylobacter

Obligate Aerobes:

No pseudo Tb + illa 4 times

Mycobacterium tuberculosis
Nocardia
Pseudomonas
Legionella
Bacillus
Brucella
Bordetella

Obligate Anaerobes:

Clostridium.

Bacteroides.

Actinomyces.

Bact Act in Closet

They lack catalase and/or superoxide dismutase.

→ oxidative damage.

Features:

Foul-smelling (due to short-chain fatty acids).
Difficult to culture in the lab.
Produce gas in tissue (CO₂ and H₂).

Treatment Challenges

Aminoglycosides ineffective (needs O₂ to enter into bacterial cell).
Antibiotic Resistance.

Facultative Anaerobes:

Staphylococcus.

Streptococcus.

Enterobacteriaceae.

Haemophilus.

Vibrio.

Microaerophilic:

5% of oxygen needed

Helicobacter, Campylobacter

pH

Usually: 7.2 to 7.6.

Except:

H. pylori: Needs acidic pH.
Proteus: Needs alkaline pH.

Temperature

Psychrophile: Grows at <20°C.

psychro - chakkara - like cold

Mesophile: Grows at 20-40°C.

meso - medium

Thermophile: Grows at 55-80°C

Bacillus geothermophilus

Intracellular

Type	Bacteria	Mnemonic
Obligate intracellular	• Rickettsia • Chlamydia • Coxiella	• Rick () has clamy () cock (Coxiella) • So he always Stay inside
Facultative intracellular	• Salmonella • Neisseria • Brucella • Mycobacterium • Listeria • Francisella • Legionella • Yersinia pestis	Facultative → • My () Salu () Yersenia () has Nice () Legs () • idakk room edukkum (facultative) • with Francis () and Bruce ()

Biofilm-Producing Bacteria

Biofilm → do film with Pseudo () skin (Epidermis) → become viral (Viridans) and influencer (Influenza)

Bacteria	Effects
Pseudomonas	• Respiratory issues • contact lens keratitis
S epidermidis	• Catheter • prosthetic device infections
Viridans streptococci	• Dental plaques • infective endocarditis
Non-typeable (unencapsulated) H influenzae	• Otitis media

Gram-positive Cocci Exception

All cocci are gram-positive except

Mnemonic: VeNoM = G -ve cocci

Veillonella
Neisseria
Moraxella
moratt nyc valli

Gram-negative Bacilli Exception

All bacilli are gram negative except

Mnemonic- MAC DONALD = G +ve bacilli

Mycobacterium
Diphtheroids
Corynebacterium diphtheria
Spore containing

Anthracis
Clostridium species

Gram positive filamentous

Nocardia
Actinomyces

Different motility

Listeria
[Yersenia (G-ve bacilli)]

Gram-positive cocci

Micrococcaceae family

Feature	Micrococcus	Staphylococcus
Shape	Tetrads	Bunch of grapes
Glucose utilization	Oxidative	Fermentative
Oxidase	Positive	Negative
Catalase	Positive	Positive

Gram Negative Baccilli

ㅤ	ㅤ
Coccobacilli	• Haemophilus • Brucella • Bordetella • Acinetobacter
Enterobacterales	• Escherichia • Klebsiella • Salmonella • Shigella • Yersinia • Proteus • Citrobacter
Spirochetes	• Treponema • Borrelia • Leptospira

Special Groups of Gram Negative Bacteria

Oxidase Positive	Mnemonic
• Vibrio • Pseudomonas • Campylobacter • Helicobacter • Micrococci • Neisseria	• Vighnesh pseudo nyc vibe on camp helicopter micropenis
Urease - positive organisms	ㅤ
• Proteus • Ureaplasma • Nocardia • Cryptococcus • H pylori • Klebsiella • S saprophyticus • S epidermidis	• Urine () passed when punched in Kleb () after eating protein () • Cried () → No…() → passed stools (sapro) 2 staph ()() chased in helicopter ()
Non-Cultivable	ㅤ
• Rickettsia • Chlamydia • T. pallidum • Mycobacterium leprae	• MRCS
Atypical Pneumonia	ㅤ
• Mycoplasma • Legionella • Chlamydia	• Atypical MLC
Not Catalase Positive	ㅤ
• Pneumococcus • Streptococcus • Enterococcus • Shigella dynsentriae	ㅤ

Bacterial Growth Curve

Lag Phase:

No increase in number of bacteria.
Increase in size, enzymes, and metabolites.
Maximum size is seen at the end of this phase.

Log Phase:

Cell division occurs.
Bacteria are smaller in size.
Shows maximum metabolic activity.

Stationary Phase:

Some bacteria viable, others dead.
Features:

Sporulation.
Toxin production (Exo Toxin).
Antibiotic production.
Bacteriocin production.

Death Phase:

Logarithmic decline
Also known as Decline phase.
Characterised by cell death.
Involution forms are seen.

Dimension And Diffusion

ㅤ	SINGLE DIMENSION	DOUBLE DIMENSION
SINGLE DIFFUSION	OUDIN	MANCINI
DOUBLE DIFFUSION	OAKLY FULTHROPE	OUCHTERLONY

Mnemonic 1

Dimension up, diffusion down

Oudin - Oakly (odunna oak)
Man - ouch

Mnemonic 2

Single single

Ou - din

Double double

Ou - chterlony (lengthy)

signle diffusion double DIMENSION

Mancini

double DIFFUSION single dimension

Fulthrope

Culture Media (CM)

https://youtube.com/shorts/-lw0wACsVEM?si=alGMsQNIDM-_XxOc

Simple/Basal Culture Media

Nutrient Agar General note

Straw-colored
White-grey colonies

Exceptions

Organism	Pigment	Notes
Staphylococcus aureus	Golden yellow pigment Optimally @ 22degree	• Non-diffusible golden pigment • Staphyloxanthene • Carotene • Aureus = Gold
Pseudomonas aeruginosa	Bluish-green pigment	• Pyocyanin, pyoverdin
Actinomyces israelii	Yellow "sulfur"	• Yellow sand israelii
Serratia marcescens	Red = Prodogiosin	• Red like Sriracha sauce

Enriched Media

Blood Agar

Normal Appearance

No zone surrounding colonies

Exceptions

Hemolysis	Seen in	Notes
α - hemolysis (partial)	Pneumococcus	• Greenish-grey zone
β - hemolysis (complete)	Staphylococcus	• Clear zone ↳ Narrow zone of hemolysis
Both α and β hemolysis	Clostridium perfringens	• Double zone/Target hemolysis • Inner zone: α-toxin/ β hemolysis • Outer zone: θ-toxin/ α hemolysis • Complete inside, incomplete outside • α is incomplete, but our β is complete • write α and theta in that order from in to out

Narrow zone of hemolysis. — **Narrow zone** of **hemolysis.**

Differential Media

Pink () Monkey ()

Cled () blue () blood

Man (Mannitol) is red (when salty experience - angry red)

Give TC (TCBS) to panchara (sucrose fermenter) & watch blue film (BTB)

MacConkey Agar

Pink color - Lactose fermentation

Only Gram-negative organisms grow

Monkey () on a pretty pink () PLANT eating lactose

P – Peptone
L – Lactose - differential media
A – Agar (Nutrient agar)
N – Neutral red - indicator media
T – Taurocholate - selective media

CLED

Cysteine Lactose Electrolyte Deficient

Gram-negative, Gram-positive, and Candida grow

Indicator - Bromothymol Blue

CLED is better as it allows gram positive and gram negative organisms to grow.

cled blue blood

Yellow colonies

Lactose fermenters (LF)

Blue colonies

Non-lactose fermenters (NLF)

Enrichment Culture Media

Purpose

Inhibits commensals in stool samples

Type	Color of CM	Pathogen
Selenite F Broth	Light brown	Salmonella, Shigella
Tetrathionate Broth	Bluish green	Salmonella, Shigella
Alkaline Peptone Water	Straw color	Vibrio

Note

NAC

Liquefies sputum

NaOH

⛔ commensals

Transport Media

Cary Blair Media (Best)

For all stool pathogens

Buffered Glycerol Saline

For all except Vibrio and Campylobacter

CAMP vs Reverse Camp

NOTE

ㅤ	CAMP	Reverse CAMP
Line	S. Aureus	C. perfringens
Arrow	S. agalactae	S. agalactae
Hemolysis	Arrow head	Arrow head
Mnemonic:	In camp, girl is brought to Gold (Aureus)	In reverse camp, gal is brought to perforate (C. perfringens)

Anaerobic Culture Media

Robertson Cooked Meat (RCM)

Best medium for anaerobic growth
Shows only anaerobic growth with meat particles
Clostridium perfringens

Shows pink colour + saccharolytic reaction.

Clostridium tetanus

Shows Black colour + proteolytic reaction

Thioglycollate Broth

Shows both aerobic and anaerobic growth

Organism-Specific Isolation Media

Organism	Media for Isolation
H influenzae	Chocolate agar Factors V (NAD⁺) and X (hematin)
N gonorrhoeae, N meningitidis	Selectively favors Neisseria Inhibits:- ↳ Gram ⊕ (vancomycin) ↳ Gram ⊝ except Neisseria (trimethoprim/colistin) ↳ Fungi (nystatin)
B pertussis	Bordet-Gengou agar
ㅤ	Regan-Lowe medium
C diphtheriae	Tellurite agar
ㅤ	Löffler medium
M tuberculosis	Löwenstein-Jensen
ㅤ	Middlebrook
ㅤ	Rapid automated broth cultures
Mycoplasma pneumoniae	Eaton agar (Requires cholesterol)
Lactose-fermenting enterics	MacConkey agar Fermentation → produce acid → pink colonies
E coli	Eosin-methylene blue (EMB) agar • Green metallic sheen
Brucella Francisella Legionella Pasteurella	Buffered charcoal yeast extract agar • Contains cysteine and iron
Fungi	Sabouraud agar

Culture Identification Tests

Note:

Organism	Gelatin stab appearance
Anthrax	Inverted fir tree appearance.
C. tetani	fir tree
V. cholerae's	turnip/napiform

1. Catalase Test

Features

Bubbles = Catalase +ve

Reaction: H₂O₂ --(catalase)--> H₂O + O₂ --(Bubbles d/t O₂ release)

No Bubbles = Catalase negative

Pneumococcus
Streptococcus
Enterococcus
Shigella dynsentriae

Clinical Relevance

Chronic granulomatous disease

NADPH oxidase deficiency

DHR > NBT

Recurrent infections with catalase ⊕ organisms

Catalase ⊕ organisms
(Mnemonic: SPACE Being Made Bubbly CATS)

Staphylococcus aureus > Golden colour.

Serratia > Red color (Prodogiosin)

Pseudomonas > Blue-green color.

Blue Nail syndrome

Candida

Enterobacteriaceae family.

Not enterococci

Escherichia coli.

Bacillus anthracis

Neisseria gonorrhoea

Neisseria meningitidis

Mycobacterium tuberculosis.

Aspergillus

Cryptococcus

Micrococcus

2. Oxidase Test

Features

vighnesh pseudo nyc vibe on camp helicopter micropenis

Pseudomonas
Vibrio cholera
Neisseria
Campylobacter
Helicobacter

3. Urease Test

Features

Pink Color = Urease +ve
Club () il protein () kazhichondirunna aale idich → he cried () → said Noooo ()
passed stools () & urine ()
2 staph ()() came behind us → we escaped in helicopter

Proteus

Ureaplasma

Nocardia

Cryptococcus

Helicobacter

Klebsiella

CONS

Staph saprophyticus
Staph epidermidis

Clinical Relevance

Predisposes to struvite (magnesium ammonium phosphate) stones

Particularly Proteus

Spore-forming bacteria

Characteristics

Some Gram ⊕ bacteria form spores when nutrients low
Spores lack metabolic activity
Resist heat/chemicals
Core has dipicolinic acid for heat resistance

Sporicidal

All sterilisation methods
Autoclave (121°C, 15 min)

ABC (Autoclave kills Bacillus and Clostridium)

Steaming (100°C, 15 min)
Chemicals: Ioo Hydrogen ethii

Hydrogen peroxide
Iodine-based agents
Ethylene oxide

Examples

Make kids (spores) in Anthra () Closet ()

Bacteria Type	Examples
Bacillus	B anthracis (anthrax)
Clostridium	Clostridium botulinum (botulism)
ㅤ	Clostridium difficile (pseudomembranous colitis)
ㅤ	Clostridium perfringens (gas gangrene)
ㅤ	Clostridium tetani (tetanus)

Bacterial Virulence Factors

Capsular polysaccharide:

Found in Streptococcus pneumonia
Over 90 known serotypes.
Identified by the Quellung reaction.
Highly charged, hydrophilic structure
Acts as barrier to phagocytosis
Acts as barrier to complement-mediated lysis
Key determinant of virulence

Protein A

Found in Staphylococcus aureus
Binds Fc region of IgG
⛔ opsonization and phagocytosis
Anticomplementary
Antiphagocytic
Co-agglutination

SHiN bacteria

Secretes IgA protease → cleaves IgA → colonize mucous membranes

Includes

S. Pneumonia
H influenza
N meningitidis

Vaccine against ACYW (Not B)

Spleen Clearance & Asplenia

Capsulated bacteria are opsonized → then cleared by the spleen
Asplenics have ↓ opsonizing ability → ↑ risk for severe infections.
SHIN Vaccine is given in Splenectomy

Also Common answer in

Has Capsule
Has Polysaccharide subunit vaccine

Also include Typhoid vaccine

Transformation ⇒ Griffith experiment
Secrete IgA Protease

Also has capsule:

Anthrayile (Bacillus Anthracis) strip(Streptococcus Pneumonia) club(Klebsiella Pneumoniae) ile staph (Staphylococcus Aureus) yersiniyakk (Yersinia Pestis) bore (Bordetella Pertussis) adich. vibe (Vibrio Parahaemolyticus) men (meningococcus) nu Hi (Hemophilus Influenza) paranju. perforate (Clostridium Perfringens) cheythappo cry (Cryptococcus) (fungus) cheythu nyceayitt (Neisseria)

M protein

Helps prevent phagocytosis
Expressed by group A Streptococci
Sequence homology with human cardiac myosin (molecular mimicry)
Autoimmune response in acute rheumatic fever

Antibiotic resistance mechanisms

Antibiotic Resistance

Types

Enzyme mediated

Aminoglycosides
β-lactamase
Chloramphenicol
Amina () Betakk () Enzyme vach Choru () koduth

Altered target

MRSA

PBP → PBP2a

VRSA

D-ala → D-lac

Macrolides
Linezolid

Efflux pump

Tetracyclines

β-lactamase

BLA gene transmitted/coded via plasmids

Enzyme by bacteria

Bind to penicillin-binding proteins (PBPs) or transpeptidases on S. aureus

break the structure of penicillin at β-lactam ring.

⇒ breakage.

Transfer: Transduction > Conjugation

Ex: H. influenza Resistance to Ampicillin

d/t production of beta lactamase

β Lactamase Inhibitors

Clavulanic acid, sulbactam and tazobactam

⛔ β-lactamase

Combinations are:

Clavulanic Acid + Amoxycillin
Sulbactam + Ampicillin
Tazobactam + Piperacillin

Penicillinase

Specific β-lactamase

Produced by Staphylococcus aureus

Acts mainly on penicillin's

Penicillinase Resistant Penicillins

Mnemonic: Put CONDOM over pencil to protect it

C → Cloxacillin
O → Oxacillin
N → Nafcillin
D → Dicloxacillin
O M → Methicillin [Most resistant]

Mnemonic: Oxa Cloxa Dicloxa + M and N

Methicillin resistance

Resistance is due to altered Penicillin Binding Proteins.

mecA gene
PBP → PBP2a

which has a lesser affinity for antibiotic binding.

Diagnosis of methicillin resistance

Cefoxitin disc diffusion agar/Oxacillin.
Latex agglutination for PBP2a.
ELISA / PCR for MecA.

MRSA treatment

DOC for MRSA : Vancomycin.
All β-lactams are ineffective

except 5th gen cephalosporins.
5th Gen:

Ceftibiprole
Ceftaroline
(With “rol”)
Against MRSA, VRSA

Daptomycin

Say Mercy Mercy (MRSA)

Valentines (Panton Valentine toxin A/w MRSA) dayil → game (γ hemolysin) played
with Hymen (Synergohymentrophic toxin) doing PV (PV toxin)

Vancomycin resistance

Vancomycin-resistant enterococcus (VRE).

VanA gene.

Mechanism:

Peptidoglycan precursor changes from

D-ala-D-ala → D-ala-D-lactate / D-ala-D-serine.

Vancomycin resistance	MIC	ㅤ
VRSA (Vancomycin-resistance S. aureus.)	>16 µg/ml vancomycin.	ㅤ
VISA (Vancomycin-intermediate S. aureus.)	>4-8 µg/ml vancomycin.	Lesser resistance.

VRSA Drugs

DOC for VRSA : Daptomycin.

Lung surfactant → break down Daptomycin

DOC for VRSA pneumonia : Linezolid.

Linezolid has good lung penetration

Streptogramins

Quinpristin + Dalfopristin

Say Mercy Mercy (MRSA)

Valentines (Panton Valentine toxin A/w MRSA) dayil → game (γ hemolysin) played
with Hymen (Synergohymentrophic toxin) doing PV (PV toxin)

Anthrayile (Bacillus Anthracis) strip(Streptococcus Pneumonia) club(Klebsiella Pneumoniae) ile staph (Staphylococcus Aureus) yersiniyakk (Yersinia Pestis) bore (Bordetella Pertussis) adich. vibe (Vibrio Parahaemolyticus) men (meningococcus) nu Hi (Hemophilus Influenza) paranju. perforate (Clostridium Perfringens) cheythappo cry (Cryptococcus) (fungus) cheythu nyceayitt (Neisseria)

General Microbiology

Scientists

Louis Pasteur

Robert Koch

Koch Postulates

Paul Ehrlich

Other Scientists

Nobel Prizes During Covid Era

Differential Stains

1. Gram Stain (+/-)

2. Acid-Fast Stain (Ziehl Neelsen Stain)

Cold Ziehl Neelsen Stain:

3. Albert Stain

4. Miscellaneous Stains

Spore stains:

Negative stain:

Silver stains:

Flagella Stain

Microscopes

1. Light Microscope

2. Dark Field Microscope

3. Interference Contrast Microscope

4. Fluorescence Microscope

5. Phase Contrast Microscope

6. Electron Microscope

Resolution

Types of electron microscope

Bacterial Anatomy

1. Capsule

Capsulated Organisms:

Composition:

2. Cell Wall

Gram-positive:

Gram-negative:

Endotoxin

Exotoxins

Superantigens Causing Shock

TOXINS CODED BY LYSOGENIC PHAGE:

3. Cell Membrane

4. Ribosomes

5. Nucleus

6. Flagella

Flagellar stain

Widal test:

Types of motility:

7. Fimbriae/Pili

Bacterial Physiology

Oxygen and Carbon Dioxide Requirements

Obligate Aerobes:

Obligate Anaerobes:

Facultative Anaerobes:

Microaerophilic:

pH

Temperature

Intracellular

Biofilm-Producing Bacteria

Gram-positive Cocci Exception

Gram-negative Bacilli Exception

Gram-positive cocci

Gram Negative Baccilli

Special Groups of Gram Negative Bacteria

Bacterial Growth Curve

Dimension And Diffusion

Culture Media (CM)

Simple/Basal Culture Media

Enriched Media

Differential Media

MacConkey Agar

CLED

Enrichment Culture Media

Transport Media

CAMP vs Reverse Camp

NOTE

Anaerobic Culture Media

Organism-Specific Isolation Media

Culture Identification Tests

1. Catalase Test

Catalase ⊕ organisms(Mnemonic: SPACE Being Made Bubbly CATS)

2. Oxidase Test

3. Urease Test

Catalase ⊕ organisms
(Mnemonic: SPACE Being Made Bubbly CATS)