Microbiology Notes for Nursing: Sterilisation, Staining, Pathogens and Infection Control

These microbiology notes for nursing cover the full exam syllabus in one place: classification and structure of bacteria, staining, sterilisation and disinfection, culture media, important pathogens, immunity, vaccines, specimen collection and infection control. Every staff nurse, AIIMS NORCET, CHO and ANM paper includes microbiology questions, and most of them are direct facts that you can score quickly if your basics are clear.

Use this page alongside our fundamentals of nursing notes, because infection control questions overlap heavily between the two subjects.

Microbiology notes for nursing: syllabus scope and weightage

In nursing recruitment exams, microbiology is a small but high-scoring subject. It usually appears as a handful of questions mixed with fundamentals and community health. Clinical, case-based questions on infection control, biomedical waste and sterilisation are now more common than pure laboratory theory.

• High priority: sterilisation and disinfection, hand hygiene, standard and transmission-based precautions, biomedical waste colour coding, specimen collection.
• Medium priority: Gram and ZN staining, culture media, hypersensitivity types, immunoglobulins, vaccine types.
• Lower priority but asked: history of microbiology, bacterial structure details, specific parasites.

History and classification of microorganisms

• Antonie van Leeuwenhoek: first to observe microorganisms (“animalcules”) with a simple microscope; father of microbiology.
• Louis Pasteur: pasteurisation, germ theory, vaccines against anthrax and rabies; father of modern microbiology.
• Robert Koch: Koch’s postulates; discovered the tubercle bacillus (1882) and Vibrio cholerae.
• Edward Jenner: smallpox vaccination (1796); father of immunology.
• Alexander Fleming: discovered penicillin (1928).

Microorganisms are grouped as bacteria (prokaryotes), viruses (acellular, contain either DNA or RNA), fungi, and parasites (protozoa and helminths). Bacteria are classified by shape:

Shape	Arrangement / example
Cocci (spherical)	Diplococci: Pneumococcus, Gonococcus, Meningococcus. Chains: Streptococcus. Clusters: Staphylococcus
Bacilli (rods)	Mycobacterium, Salmonella, E. coli, Clostridium
Comma shaped	Vibrio cholerae
Spirochaetes	Treponema pallidum, Leptospira, Borrelia
Club shaped	Corynebacterium diphtheriae (Chinese letter arrangement)

By oxygen requirement, bacteria are obligate aerobes (M. tuberculosis), obligate anaerobes (Clostridium), facultative anaerobes (most enteric bacteria) and microaerophilic (Helicobacter, Campylobacter).

Bacterial structure

Structure	Function / exam point
Cell wall	Made of peptidoglycan. Gram positive: thick wall with teichoic acid. Gram negative: thin wall plus outer membrane with lipopolysaccharide (endotoxin)
Capsule	Prevents phagocytosis; major virulence factor (Pneumococcus, Klebsiella)
Flagella	Organs of motility: monotrichous, lophotrichous, amphitrichous, peritrichous
Pili (fimbriae)	Adhesion to host cells; sex pili transfer genetic material in conjugation
Spores	Highly resistant resting forms of Bacillus and Clostridium; the reason why sterilisation must kill spores
Plasmids	Extrachromosomal DNA; carry drug resistance genes
Ribosomes	70S type; site of action of many antibiotics

Bacteria multiply by binary fission. The growth curve has four phases: lag, log (exponential), stationary and decline (death) phase.

Staining techniques: Gram and Ziehl-Neelsen

Gram staining (Hans Christian Gram, 1884)

1. Primary stain: crystal violet
2. Mordant: Gram’s iodine
3. Decolouriser: acetone or alcohol
4. Counterstain: safranin (or dilute carbol fuchsin)

Gram positive bacteria retain crystal violet and appear purple/violet. Gram negative bacteria lose it at decolourisation and take the counterstain, appearing pink/red.

Ziehl-Neelsen (acid-fast) staining

1. Primary stain: strong carbol fuchsin with heating
2. Decolouriser: 20% sulphuric acid for M. tuberculosis (5% for M. leprae)
3. Counterstain: methylene blue

Acid-fast bacilli appear red/pink rods on a blue background. Acid fastness is due to mycolic acid in the cell wall. Other stains to remember: Albert’s stain for metachromatic granules of C. diphtheriae, India ink for the capsule of Cryptococcus, and KOH mount for fungi.

Sterilisation and disinfection

Sterilisation kills all microorganisms including spores. Disinfection kills most pathogens but not necessarily spores. Antiseptics are disinfectants safe for living tissue.

Physical methods

Method	Standard conditions	Used for
Autoclave (moist heat under pressure)	121 degrees C, 15 lb/sq inch, 15 minutes (or 134 degrees C for 3 minutes)	Surgical instruments, linen, dressings, culture media
Hot air oven (dry heat)	160 degrees C for 2 hours (170 degrees C 1 hour, 180 degrees C 30 minutes)	Glassware, powders, oils, sharp instruments
Pasteurisation	Holder: 63 degrees C for 30 minutes. Flash: 72 degrees C for 15 to 20 seconds	Milk (not sterilisation)
Boiling	100 degrees C for 10 to 30 minutes	Disinfection only; spores may survive
Tyndallisation	100 degrees C for 20 minutes on 3 successive days	Sugar and gelatin media
Inspissation	80 to 85 degrees C for 30 minutes on 3 successive days	LJ medium, Loeffler’s serum slope
Red heat / flaming	Held in flame till red hot	Inoculating loops, forceps tips
Incineration	Burning to ash	Anatomical and soiled waste
Ionising radiation (gamma rays)	“Cold sterilisation”	Disposable syringes, catheters, sutures
Ultraviolet rays	Wavelength around 260 nm, poor penetration	Air and surfaces in OT, labs
Filtration	Membrane filters 0.22 micron; HEPA filters for air	Sera, antibiotic and heat-labile solutions

Biological indicators: spores of Geobacillus (Bacillus) stearothermophilus for the autoclave and spores of a non-toxigenic strain of Clostridium tetani or Bacillus atrophaeus for the hot air oven. Bowie-Dick test checks air removal in a prevacuum autoclave.

Chemical methods

Agent	Key points
Alcohol (ethyl or isopropyl)	Most effective at 60 to 70%, not absolute; not sporicidal; skin antisepsis
Glutaraldehyde 2% (Cidex)	High-level disinfection of endoscopes in about 20 minutes; sterilisation needs about 10 hours
Ethylene oxide gas	Sterilises heat-sensitive plastics, heart-lung machines; toxic and explosive, needs aeration
Formaldehyde	Fumigation of OT and wards (with potassium permanganate)
Sodium hypochlorite	1% for blood and body fluid spills; corrodes metals
Chlorhexidine, povidone iodine	Skin and surgical hand antisepsis
Hydrogen peroxide plasma	Low-temperature sterilisation of delicate instruments

Spaulding classification

• Critical items (enter sterile tissue or blood: surgical instruments, implants, urinary catheters): need sterilisation.
• Semi-critical items (contact mucous membranes: endoscopes, laryngoscope blades): need high-level disinfection at least.
• Non-critical items (contact intact skin: BP cuff, bedpan): low-level disinfection.

Culture media

Type	Examples and use
Simple / basal	Nutrient agar, nutrient broth, peptone water
Enriched	Blood agar (haemolysis pattern), chocolate agar (Haemophilus, Neisseria)
Selective	LJ medium (M. tuberculosis), TCBS (Vibrio cholerae), Wilson and Blair (S. typhi), DCA (Salmonella, Shigella), Thayer-Martin (N. gonorrhoeae), potassium tellurite (C. diphtheriae)
Enrichment broth	Selenite F and tetrathionate broth (Salmonella), alkaline peptone water (Vibrio)
Differential	MacConkey agar: lactose fermenters pink (E. coli), non-fermenters pale (Salmonella, Shigella)
Transport	Stuart’s and Amies (swabs), Cary-Blair and VR fluid (stool for cholera)
Anaerobic	Robertson’s cooked meat medium
Fungal	Sabouraud’s dextrose agar

Loeffler’s serum slope gives rapid growth of C. diphtheriae. Agar is obtained from seaweed and is used only as a solidifying agent, not a nutrient.

Important bacteria, viruses, fungi and parasites

Organism	Disease	Exam clue
Mycobacterium tuberculosis	Tuberculosis	Acid-fast, slow growing; LJ medium; CBNAAT/TrueNat for diagnosis
Mycobacterium leprae	Leprosy	Cannot be grown in artificial media; armadillo, mouse footpad
Salmonella typhi	Enteric fever	Blood culture positive in first week; Widal test after first week
Vibrio cholerae	Cholera	Rice-water stools, darting motility
Corynebacterium diphtheriae	Diphtheria	Greyish pseudomembrane, bull neck
Clostridium tetani	Tetanus	Drumstick spores, lockjaw, risus sardonicus, opisthotonus
Bordetella pertussis	Whooping cough	Paroxysmal cough with inspiratory whoop
Streptococcus pyogenes	Pharyngitis	Can lead to rheumatic fever and acute glomerulonephritis
Staphylococcus aureus	Boils, wound infection	Coagulase positive; MRSA common in hospitals
Treponema pallidum	Syphilis	Dark ground microscopy; VDRL screening
HIV	AIDS	Retrovirus (RNA); attacks CD4 T cells
Hepatitis B virus	Hepatitis B	DNA virus; blood, sexual and vertical spread; HBsAg
Hepatitis A and E viruses	Infective hepatitis	Faeco-oral spread; HEV dangerous in pregnancy
Rabies virus	Rabies	Bullet-shaped rhabdovirus; Negri bodies
Measles virus	Measles	Koplik spots
Dengue virus	Dengue	Flavivirus; Aedes aegypti, day biter
Candida albicans	Thrush, candidiasis	Opportunistic in diabetes, antibiotics, HIV
Cryptococcus neoformans	Meningitis in HIV	India ink capsule
Plasmodium (vivax, falciparum)	Malaria	Female Anopheles; thick and thin peripheral smear
Entamoeba histolytica	Amoebic dysentery, liver abscess	“Anchovy sauce” pus
Ancylostoma duodenale	Hookworm infection	Iron deficiency anaemia; enters through bare feet
Enterobius vermicularis	Pinworm	Perianal itching at night; cellophane tape test
Wuchereria bancrofti	Lymphatic filariasis	Culex mosquito; night blood smear
Leishmania donovani	Kala-azar	Sandfly vector

Immunity, immunoglobulins and hypersensitivity

Types of immunity

Type	Natural	Artificial
Active (body makes antibodies, long lasting, slow onset)	After clinical or subclinical infection	Vaccination
Passive (ready-made antibodies, immediate, short lived)	Maternal IgG across placenta, IgA in breast milk	Immunoglobulins and antisera (rabies immunoglobulin, tetanus immunoglobulin)

Immunoglobulins

• IgG: most abundant, crosses the placenta, main antibody of secondary response.
• IgM: largest (pentamer), first antibody formed; indicates recent infection.
• IgA: secretory antibody in colostrum, saliva, tears and mucosa.
• IgE: allergy, anaphylaxis and worm infestations; binds mast cells.
• IgD: receptor on B cells.

Hypersensitivity reactions (Gell and Coombs)

Type	Mechanism	Examples
Type I (immediate, anaphylactic)	IgE on mast cells, histamine release	Anaphylaxis, bronchial asthma, hay fever, urticaria
Type II (cytotoxic)	IgG/IgM against cell surface antigens	Mismatched blood transfusion, Rh haemolytic disease of newborn, Goodpasture syndrome
Type III (immune complex)	Antigen-antibody complexes deposit in tissues	Serum sickness, Arthus reaction, SLE, post-streptococcal glomerulonephritis
Type IV (delayed, cell mediated)	Sensitised T cells, 48 to 72 hours	Mantoux test, contact dermatitis, graft rejection

Anaphylaxis is managed first with intramuscular adrenaline (1:1000) in the anterolateral thigh, along with airway support. This is covered in detail in our pharmacology nursing notes.

Types of vaccines

Type	Examples
Live attenuated	BCG, OPV, measles-rubella, rotavirus, yellow fever, varicella, JE (SA 14-14-2)
Killed / inactivated	IPV, cell culture rabies vaccine, whole cell pertussis, hepatitis A (inactivated)
Toxoid	Tetanus toxoid, diphtheria toxoid (Td)
Subunit / recombinant	Hepatitis B, HPV
Conjugate	Hib, pneumococcal conjugate vaccine (PCV)

Live vaccines are generally avoided in pregnancy and severe immunodeficiency. OPV is the most heat-sensitive vaccine, while Hepatitis B, pentavalent, Td, IPV and PCV are freeze-sensitive (check with the shake test). The full national schedule is in our pediatric nursing notes.

Specimen collection: nursing points

• Collect specimens before starting antibiotics, label at the bedside and send to the lab promptly with a requisition form.
• Urine: clean-catch midstream sample; in catheterised patients aspirate from the sampling port, never from the drainage bag. If delay is expected, refrigerate at 4 degrees C.
• Blood culture: strict skin antisepsis, at least two sets from different sites, adequate volume per bottle, collected during or before fever spike.
• Sputum for TB: deep coughed sample (not saliva), early morning sample preferred, in a wide-mouthed sterile container.
• CSF: send immediately and never refrigerate (Meningococcus is sensitive to cold).
• Stool: fresh sample in a clean container; for cholera use Cary-Blair or VR fluid if transport is delayed.
• Swabs: use the transport medium provided; avoid touching surrounding skin.

Hospital acquired infections and standard precautions

A hospital acquired (nosocomial, healthcare-associated) infection is one that was not present or incubating at admission and appears 48 hours or more after admission. Common types are catheter-associated urinary tract infection (CAUTI, the most common in many settings), central line associated bloodstream infection (CLABSI), ventilator associated pneumonia (VAP) and surgical site infection (SSI). Common organisms include MRSA, Pseudomonas aeruginosa, Klebsiella, E. coli, Acinetobacter and Clostridioides difficile.

Standard precautions (for every patient)

• Hand hygiene following the WHO “5 moments”: before touching a patient, before a clean/aseptic procedure, after body fluid exposure risk, after touching a patient, after touching patient surroundings.
• Alcohol hand rub takes 20 to 30 seconds; soap and water hand wash takes 40 to 60 seconds and is needed when hands are visibly soiled or after C. difficile exposure.
• PPE according to risk, respiratory hygiene and cough etiquette, safe injection practices (one needle, one syringe, one time), no recapping of needles, environmental cleaning, safe handling of linen and biomedical waste.

Transmission-based precautions

Type	Examples	Key measure
Contact	MRSA, C. difficile, scabies	Gloves and gown, dedicated equipment
Droplet (particles over 5 microns)	Influenza, mumps, pertussis, meningococcal infection, diphtheria	Surgical mask within about 1 metre, single room or cohorting
Airborne (particles under 5 microns)	Tuberculosis, measles, varicella	N95 respirator, negative pressure isolation room

CDC sequence for PPE: donning is gown, mask/respirator, goggles or face shield, gloves. Doffing is gloves, goggles or face shield, gown, mask/respirator, followed by hand hygiene.

Biomedical Waste Management Rules, 2016: colour coding

Category	Waste
Yellow	Human anatomical waste, soiled dressings, expired medicines, chemical waste, microbiology lab waste (pre-treated)
Red	Contaminated recyclable plastics: IV sets, catheters, tubing, syringes without needles, gloves
White (translucent, puncture proof)	Needles, blades, other metal sharps
Blue (cardboard box)	Glassware, broken vials, metallic body implants

After a needle-stick injury: wash with soap and running water, do not squeeze or suck the wound, report immediately and start post-exposure prophylaxis as early as possible (ideally within 2 hours, not beyond 72 hours) for 28 days if indicated.

Quick revision points

• Father of microbiology: Leeuwenhoek; father of modern microbiology: Louis Pasteur.
• Autoclave standard: 121 degrees C, 15 lb/sq inch, 15 minutes.
• Hot air oven standard: 160 degrees C for 2 hours.
• Biological indicator for autoclave: Geobacillus stearothermophilus.
• Most effective concentration of alcohol: 60 to 70%.
• Endoscopes are disinfected with 2% glutaraldehyde.
• Gram positive bacteria appear purple; Gram negative appear pink.
• Decolouriser in ZN stain for M. tuberculosis: 20% sulphuric acid.
• LJ medium is used for M. tuberculosis; TCBS for Vibrio cholerae.
• MacConkey agar is a differential medium for lactose fermenters.
• Only immunoglobulin to cross the placenta: IgG. Largest: IgM. In colostrum: IgA.
• Mantoux test is a type IV hypersensitivity reaction.
• Rh haemolytic disease of newborn is type II hypersensitivity.
• Tetanus and diphtheria vaccines are toxoids.
• TB, measles and varicella need airborne precautions with N95.
• CSF samples should never be refrigerated.
• Needles go in the white puncture-proof container; IV tubing in red.

For the related topics of disease control and immunisation programmes, read our community health nursing notes and national health programmes notes. To see where this subject fits in the overall exam, check the NORCET exam pattern and syllabus guide, then test yourself in the NORCET test series. CHO and ANM aspirants can follow the subject in the CHO courses and ANM courses.

Frequently asked questions

How many microbiology questions come in nursing exams?

The number varies by exam and year and is not fixed officially. Microbiology usually contributes a small set of questions, often mixed with infection control and fundamentals, so it is a quick-scoring subject rather than a major one.

Which microbiology topics are most important for AIIMS NORCET?

Sterilisation and disinfection, hand hygiene, isolation precautions, biomedical waste segregation, specimen collection and hypersensitivity reactions are the most frequently tested areas. Clinical scenario questions on infection control are increasingly common.

What is the difference between sterilisation and disinfection?

Sterilisation destroys all forms of microbial life including bacterial spores, for example by autoclaving. Disinfection removes most pathogenic organisms but may not kill spores, for example by boiling or using 70% alcohol.

What are the autoclave settings asked in exams?

The standard answer is 121 degrees C at 15 lb per square inch pressure for 15 minutes. Flash sterilisation uses 134 degrees C for about 3 minutes.

Are these microbiology notes enough for CHO and ANM exams?

They cover the core syllabus, but CHO and ANM papers link microbiology with community health, immunisation and national programmes. Read the related subject notes and practise MCQs regularly for full coverage.