Microbiology for nurses

In short

Microbiology for nurses is the study of micro-organisms — bacteria, viruses, fungi, protozoa and helminths — and of how they cause infection, how they are identified in the laboratory, and how they are killed or kept away from patients. It is the scientific basis of every aseptic act at the bedside: hand hygiene, sterile dressing, catheter care, waste segregation and immunisation. It is examined in the first-year B.Sc Nursing Microbiology paper (INC syllabus, written plus practical), and re-tested in NORCET/AIIMS, state nursing officer, ESIC, RRB and DSSSB recruitment papers, where infection-control questions are among the most frequent. On the job it governs NABH/JCI infection-control audits, HAI surveillance, CSSD practice and compliance with the Bio-Medical Waste Management Rules, 2016.

Explained

Scope, classification and morphology of micro-organisms

• Microbiology: science of organisms too small to be seen with the naked eye (roughly below 0.1 mm). Branches: bacteriology, virology, mycology, parasitology, immunology.
• Prokaryote vs eukaryote: bacteria are prokaryotes — no nuclear membrane, no mitochondria, 70S ribosomes, peptidoglycan cell wall. Fungi, protozoa and human cells are eukaryotes (80S ribosomes, true nucleus). This difference is why antibacterials spare human cells.
• Bacterial shapes: cocci (round) — in chains (*Streptococcus*), clusters (*Staphylococcus*), pairs (*Neisseria*, pneumococcus); bacilli (rods) — *E. coli*, *Klebsiella*; curved/spiral — *Vibrio cholerae* (comma), *Treponema pallidum* (spirochaete); *Mycobacterium* (acid-fast rod).
• Structures: capsule (anti-phagocytic, virulence), cell wall (shape, Gram reaction), flagella (motility), pili/fimbriae (adhesion, conjugation), plasmid (extra-chromosomal DNA, carries resistance genes), spore (dormant, heat-resistant form of *Bacillus* and *Clostridium*).
• Gram stain (Christian Gram): crystal violet → Gram's iodine (mordant) → acetone/alcohol (decolouriser) → safranin/carbol fuchsin (counterstain). Gram-positive retain violet (thick peptidoglycan); Gram-negative appear pink/red (thin wall, outer lipopolysaccharide membrane = endotoxin).
• Ziehl–Neelsen (acid-fast) stain: carbol fuchsin with heat → 20–25% sulphuric acid → methylene blue; *M. tuberculosis* and *M. leprae* stay red because of mycolic acid in the wall.
• Other organisms: viruses (obligate intracellular, DNA or RNA, need living cells; e.g. hepatitis B, HIV, dengue, influenza, SARS-CoV-2); fungi (yeast — *Candida*; mould — *Aspergillus*; dimorphic); protozoa (*Plasmodium*, *Entamoeba histolytica*, *Giardia*); helminths (roundworm, hookworm, tapeworm); ectoparasites (scabies mite, lice).
• Growth requirements: temperature (mesophiles 25–40 °C; most pathogens 37 °C), pH near 7.2–7.4, oxygen (aerobe, anaerobe, facultative, microaerophilic), moisture, nutrients.
• Growth curve phases: lag → log (exponential; most sensitive to antibiotics) → stationary → decline/death. Generation time of *E. coli* ≈ 20 minutes; of *M. tuberculosis* ≈ 15–20 hours (hence long therapy).

Infection, chain of transmission and host defence

• Terms: infection (entry and multiplication of an organism in the host); colonisation (presence without tissue damage); contamination (organisms on an inanimate surface); carrier (harbours and sheds organism without illness — Typhoid Mary); pathogenicity (ability to cause disease); virulence (degree of that ability).
• Chain of infection (six links): 1 infectious agent → 2 reservoir (human, animal, soil, water) → 3 portal of exit (respiratory, GI, blood, skin) → 4 mode of transmission → 5 portal of entry → 6 susceptible host. Infection control works by breaking any link; hand hygiene breaks link 4, which is the easiest and cheapest to break.
• Modes of transmission: contact (direct and indirect/fomite), droplet (large droplets, up to about 1–2 m — influenza, pertussis, meningococcus), airborne (droplet nuclei under 5 µm, remain suspended — tuberculosis, measles, varicella), vehicle-borne (food, water, blood), vector-borne (*Aedes* — dengue/chikungunya; *Anopheles* — malaria), vertical (mother to child: HIV, hepatitis B, rubella, syphilis).
• Epidemiological terms: incubation period, prodromal, acute, convalescent stages; endemic, epidemic/outbreak, pandemic, sporadic; zoonosis (rabies, brucellosis); nosocomial/HAI (acquired after 48 hours of admission); iatrogenic (resulting from a procedure); opportunistic (in the immunocompromised).
• Non-specific (innate) defence: intact skin, mucus and cilia, gastric acid, lysozyme in tears, normal flora, inflammation, phagocytosis by neutrophils and macrophages, fever, complement, interferon.
• Specific (acquired) immunity:
  • Humoral — B lymphocytes → plasma cells → antibodies (immunoglobulins). IgG (most abundant, crosses placenta, secondary response), IgM (largest, first/primary response, indicates recent infection), IgA (secretory — breast milk, saliva, gut), IgE (allergy, parasites), IgD (B-cell receptor).
  • Cell-mediated — T lymphocytes: helper T (CD4, destroyed by HIV), cytotoxic T (CD8), regulatory T; acts against viruses, tubercle bacilli, fungi, tumours and transplants.
• Types of immunity: active natural (after illness), active artificial (vaccine), passive natural (maternal IgG via placenta, IgA via colostrum), passive artificial (immunoglobulin, antiserum, ATS/anti-rabies immunoglobulin). Active = slow onset, long lasting, memory; passive = immediate, short lasting, no memory.
• Hypersensitivity: Type I immediate/anaphylactic (IgE — penicillin anaphylaxis); Type II cytotoxic (haemolytic transfusion reaction); Type III immune-complex (serum sickness, post-streptococcal glomerulonephritis); Type IV delayed cell-mediated (Mantoux test, contact dermatitis).
• Vaccines: live attenuated (BCG, OPV, MR, rotavirus, varicella — avoid in pregnancy and severe immunodeficiency), killed/inactivated (IPV, rabies, hepatitis A, whole-cell typhoid), toxoid (TT, Td), subunit/conjugate (hepatitis B, PCV, Hib, HPV), mRNA and viral-vector (COVID-19). Cold chain: vaccines stored +2 to +8 °C in ILR; OPV and measles-containing vaccines are the most heat-sensitive; never freeze TT, Td, hepatitis B or PCV — freezing is detected by the shake test; the vaccine vial monitor (VVM) stages 1–2 are usable, 3–4 discard.
• Universal Immunisation Programme (India, broad schedule — check the current state/NHM card, as additions happen): birth — BCG, OPV-0, hepatitis B birth dose; 6, 10, 14 weeks — pentavalent (DPT+HepB+Hib), OPV, rotavirus, fIPV, PCV; 9–12 months — MR 1st, JE 1st (endemic districts), vitamin A; 16–24 months — MR 2nd, DPT booster 1, OPV booster, JE 2nd; 5–6 years — DPT booster 2; 10 and 16 years — Td; pregnancy — Td ×2 or booster.

Sterilisation, disinfection and asepsis

• Definitions: sterilisation destroys all forms of microbial life including spores; disinfection destroys pathogens but not necessarily spores (used on inanimate objects); antisepsis uses chemicals on living tissue; sanitisation reduces counts to a safe level; decontamination removes or inactivates organisms to make an item safe to handle; cleaning physically removes soil and is the mandatory first step before any sterilisation.
• Spaulding classification: *critical* items enter sterile tissue or the bloodstream (surgical instruments, implants, needles) → sterilisation; *semi-critical* touch mucous membranes (endoscopes, laryngoscope blades, respiratory circuits) → high-level disinfection; *non-critical* touch intact skin (BP cuff, stethoscope, bedpan) → low/intermediate-level disinfection.
• Physical methods:
  • Moist heat (autoclave, steam under pressure) — the standard hospital method: 121 °C at 15 psi (≈1.05 kg/cm², 103 kPa) for 15–20 min, or 134 °C at 30 psi for 3–4 min. Used for linen, dressings, instruments, rubber goods, culture media. Kills by coagulating protein; far more effective than dry heat at the same temperature.
  • Dry heat (hot-air oven) — 160 °C for 2 hours or 170 °C for 1 hour; for glassware, powders, oils, metal instruments. Incineration for anatomical waste; red heat for inoculating loops; flaming for scalpel and slide.
  • Boiling — 100 °C for 10–30 min: disinfection only, does not kill spores.
  • Pasteurisation of milk — holder 63 °C/30 min, HTST flash 72 °C/15–20 s, UHT 125–150 °C/seconds; phosphatase test confirms adequacy.
  • Filtration — membrane filter 0.22 µm for sera, antibiotic solutions, vitamins; HEPA filters for operation theatres and laminar-flow hoods.
  • Radiation — ultraviolet (254 nm, non-ionising, surface only, no penetration, harmful to eyes/skin) for OT and laboratory air; gamma rays (ionising, cobalt-60) for industrial sterilisation of syringes, gloves, catheters, sutures.
• Chemical methods: alcohol 60–90% (skin, surfaces; poor against spores and non-enveloped viruses); chlorine/sodium hypochlorite 1% for blood spills and 0.5% for general decontamination; iodophor and povidone-iodine (skin prep); chlorhexidine 2% with 70% alcohol for skin antisepsis and central line insertion; hydrogen peroxide; glutaraldehyde 2% (20 min high-level disinfection, 10 hours sterilisation — endoscopes); formaldehyde (fumigation, now largely replaced by hydrogen-peroxide vapour); ethylene oxide gas for heat-labile plastics and electronics; plasma sterilisation (hydrogen peroxide gas plasma).
• Sterilisation monitoring: *physical* — temperature, pressure and time charts; *chemical* — autoclave tape, Bowie–Dick test for air removal, TST strips; *biological* (the only proof of lethality) — spores of *Geobacillus stearothermophilus* for moist heat and *Bacillus atrophaeus* for dry heat/ETO.
• Factors reducing effectiveness: organic soil (blood, pus), high bio-burden, improper packing/overloading, trapped air, wrong dilution of disinfectant, expired or reused solution, too-short contact time.

Specimen collection, laboratory diagnosis and the nurse's role

• Golden rules: collect before starting antibiotics; use the right sterile container; adequate quantity; correct site and timing; label with name, hospital number, date, time, specimen type and ward; fill the request form with clinical details; transport promptly (within about 1–2 hours; refrigerate at 4 °C if delayed — except CSF and blood cultures, which must never be refrigerated); treat every specimen as infectious and carry it in a leak-proof bag.
• Blood culture: 2 sets from 2 different sites before antibiotics, at the time of fever/rigor; clean the skin with 2% chlorhexidine-alcohol and let it dry; 8–10 mL per bottle in adults, 1–3 mL in children; a 1:10 blood-to-broth ratio. Common contaminant: coagulase-negative *Staphylococcus* from skin.
• Urine: clean-catch midstream in a sterile wide-mouth container; early-morning sample; for catheterised patients sample from the port, never from the bag; significant bacteriuria ≥10⁵ CFU/mL of a single organism (lower thresholds apply in symptomatic women and in suprapubic/catheter samples).
• Sputum: early-morning deep-cough sample, not saliva; two samples for NTEP (now commonly one spot plus one morning sample, with NAAT/CBNAAT as the first-line test); for TB use a wide-mouth leak-proof container and avoid aerosol generation.
• Stool: fresh sample in a clean container; examine within 1 hour for motile trophozoites of *E. histolytica*; rectal swab or transport medium (Cary–Blair) if delay; "rice-water" stool in cholera.
• CSF: collected by the doctor during lumbar puncture into three sterile tubes (cell count, biochemistry, microbiology); never refrigerate; transport immediately — *Neisseria meningitidis* dies quickly.
• Swabs: wound/throat swab with a sterile cotton swab from the active margin, before antiseptic application; use transport medium (Stuart's/Amies) if delay.
• Laboratory methods: direct microscopy (wet mount, Gram, ZN, India ink, KOH for fungi, dark-field for spirochaetes); culture media — simple (nutrient agar), enriched (blood agar, chocolate agar), selective (MacConkey for enterics, Lowenstein–Jensen for TB, TCBS for *Vibrio*), differential (blood agar for haemolysis), transport, anaerobic; biochemical tests (catalase, coagulase, oxidase, urease); serology (ELISA, rapid card tests, Widal, VDRL/RPR); molecular — PCR, CBNAAT/Truenat for TB with rifampicin resistance; antigen tests; automated systems (BacT/ALERT, VITEK, MALDI-TOF).
• Antibiotic sensitivity: Kirby–Bauer disc diffusion on Mueller–Hinton agar with zone-diameter interpretation (CLSI breakpoints), or MIC by broth microdilution/automated panels. Report: S (sensitive), I (intermediate), R (resistant).
• Antimicrobial resistance (AMR): mechanisms — enzymatic destruction (beta-lactamase, ESBL, carbapenemase/NDM-1), altered target, reduced permeability, efflux pumps. Important resistant organisms: MRSA, VRE, ESBL and carbapenem-resistant *Enterobacterales* (CRE), MDR/XDR-TB, *Candida auris*. Drivers: over-prescription, no culture before therapy, incomplete courses, over-the-counter sales, veterinary and agricultural use. India's response: National Action Plan on AMR, ICMR's AMR surveillance network and treatment guidelines, Schedule H1 of the Drugs and Cosmetics Rules (restricting sale of specified antibiotics), hospital antibiotic stewardship programmes and antibiotic policies required under NABH.

Infection control practice in the hospital

• Standard (universal) precautions apply to every patient regardless of diagnosis — treat all blood, body fluids, secretions, excretions (except sweat), non-intact skin and mucous membranes as infectious: hand hygiene, PPE, safe injection practice, respiratory hygiene, safe handling of linen and sharps, environmental cleaning, patient placement.
• WHO 5 moments of hand hygiene: 1 before touching a patient; 2 before a clean/aseptic procedure; 3 after body-fluid exposure risk; 4 after touching a patient; 5 after touching patient surroundings. Alcohol-based hand rub 20–30 s for visibly clean hands; soap-and-water handwash 40–60 s when hands are soiled, after using the toilet and in *C. difficile* or spore exposure (alcohol does not kill spores). Surgical hand scrub 2–5 min. Technique: WHO 6/7 steps, remember to clean the thumbs, fingertips and web spaces — the most commonly missed areas.
• Transmission-based precautions (added to standard): *contact* — gown and gloves, dedicated equipment (MRSA, CRE, scabies, *C. difficile*); *droplet* — surgical mask within 1 m, patient masked during transport (influenza, pertussis, mumps, meningococcus); *airborne* — N95/FFP2 respirator, negative-pressure or well-ventilated single room, door closed (TB, measles, varicella, disseminated zoster).
• PPE sequence: don — hand hygiene, gown, mask/respirator, goggles/face shield, gloves. Doff — gloves, goggles, gown, mask last (the most contaminated items come off first; the mask is removed outside the room), with hand hygiene between steps and at the end.
• Common HAIs and their prevention bundles: CAUTI (catheterise only when indicated, aseptic insertion, closed drainage, bag below bladder level and off the floor, no routine change, remove early); CLABSI (maximal sterile barriers, chlorhexidine skin prep, subclavian preference, daily review of need, scrub the hub); VAP (head of bed 30–45°, daily sedation break and extubation assessment, oral care with chlorhexidine, subglottic suction); SSI (no shaving — clip if needed, antibiotic prophylaxis within 60 min of incision, normothermia, glycaemic control); *C. difficile* diarrhoea after broad-spectrum antibiotics.
• Needle-stick/sharps injury protocol: do not squeeze or suck; wash with soap and running water; do not use bleach on the wound; flush mucosa/eyes with water or saline; report immediately to the infection-control nurse; test source and recipient (HIV, HBV, HCV); start HIV post-exposure prophylaxis (three-drug ART) as soon as possible, ideally within 2 hours and up to 72 hours, for 28 days; hepatitis B immunoglobulin plus vaccine if unvaccinated/non-responder; follow-up testing; record in the exposure register. Prevention: never recap needles (or use one-hand scoop), use safety-engineered devices, discard at point of use, never overfill the sharps container (three-quarters full).
• Sharps and injection safety: one needle, one syringe, one patient, one time; single-dose vials preferred; needle hub cutter at point of care for syringes as specified in the BMW rules.
• Isolation types: standard/source isolation (to protect others), protective/reverse isolation (to protect a neutropenic or transplant patient), cohorting during outbreaks.
• Environment and surveillance: OT fumigation/terminal cleaning, laminar air flow and HEPA filters, air changes per hour, 1% hypochlorite for blood spills (cover with absorbent material, pour disinfectant, wait 10 min, remove with gloves), high-touch surface cleaning twice daily, biomedical equipment disinfection between patients; HAI surveillance with device-associated infection rates reported by the Hospital Infection Control Committee (HICC), which NABH accreditation requires.
• Bio-Medical Waste Management Rules, 2016 (amended; under the Environment (Protection) Act, 1986) — colour coding:
  • Yellow — human anatomical and animal waste, soiled waste (dressings, cotton, blood bags), expired/discarded medicines, chemical waste, laboratory and microbiology waste, used linen: incineration/plasma pyrolysis/deep burial.
  • Red — contaminated recyclable plastic: tubing, bottles, IV sets, catheters, urine bags, syringes without needles, gloves: autoclave/microwave/hydroclave then shred and recycle through authorised recyclers.
  • White (translucent, puncture-proof) — sharps: needles, syringes with fixed needles, needles cut by the hub cutter, scalpels, blades and other contaminated sharp metal objects: sterilise then shred/encapsulate.
  • Blue (cardboard box with blue marking) — broken or discarded glass vials and metallic implants: disinfect and recycle.
  • General (black bin) non-hazardous municipal waste is outside these four categories. Other requirements: no untreated waste to be stored beyond 48 hours, barcoding and annual report to the State Pollution Control Board, pre-treatment of laboratory and microbiology waste on site, training and immunisation (hepatitis B, tetanus) of waste handlers.
• Related Indian framework: Clinical Establishments (Registration and Regulation) Act, 2010 and NABH standards (infection-control programme, HICC, antibiotic policy); Epidemic Diseases Act, 1897; National Health Programmes — NTEP for TB, NACP for HIV/AIDS, NVBDCP for vector-borne disease, National Rabies Control Programme, National Viral Hepatitis Control Programme; IDSP/IHIP for notifiable-disease reporting.

Important pathogens a nurse must recognise

• *Staphylococcus aureus* — Gram-positive cocci in clusters, catalase and coagulase positive; boils, abscess, wound infection, food poisoning (preformed toxin, 1–6 h), toxic shock; nasal carriage is the reservoir; MRSA needs contact precautions and vancomycin.
• *Streptococcus pyogenes* (Group A) — sore throat, scarlet fever, erysipelas, cellulitis; late sequelae rheumatic fever and acute glomerulonephritis; ASO titre; penicillin remains effective.
• *Mycobacterium tuberculosis* — acid-fast, slow-growing, airborne; diagnosed by CBNAAT/Truenat, ZN microscopy, culture on LJ medium, chest X-ray; treated under NTEP with daily fixed-dose combinations (2 months HRZE intensive + 4 months HRE continuation for drug-sensitive pulmonary TB; regimens and the Ni-kshay incentive amount are revised periodically — confirm the current NTEP guideline); nurse's role: DOT, airborne precautions, cough etiquette, contact tracing, notification.
• *Vibrio cholerae* — rice-water stools; management is ORS and IV Ringer lactate with doxycycline; water-borne.
• *Salmonella* Typhi — enteric fever, step-ladder fever; blood culture is best in week 1, stool/urine later, Widal from week 2 (low specificity in endemic India); chronic gall-bladder carriers.
• *Clostridium tetani* — spore-forming anaerobe from soil; toxin-mediated trismus and risus sardonicus; prevention by Td/TT and wound toilet; tetanus immunoglobulin for treatment.
• *Neisseria gonorrhoeae*/*Treponema pallidum* — STIs; syphilis diagnosed with VDRL/RPR screening confirmed by TPHA.
• Hepatitis B and C, HIV — blood-borne; HBV is the most infectious per needle-stick (roughly 6–30% transmission risk, against about 1.8% for HCV and 0.3% for HIV); HBV is vaccine-preventable — a 3-dose course is mandatory for nursing students and staff.
• Dengue (*Aedes aegypti*) — NS1 antigen in the first 5 days, IgM later; warning signs, platelet monitoring, no NSAIDs/aspirin; day-biting mosquito, breeds in clean stored water.
• Malaria — *P. vivax* and *P. falciparum*; rapid diagnostic test and peripheral smear; artemisinin-based combination therapy for falciparum; *Anopheles* bites at night — bed nets (LLIN).
• Hospital fungi — *Candida* (catheters, broad-spectrum antibiotics, diabetes), *Aspergillus* (construction dust, neutropenic patients).

Key points

• Sterilisation - kills all microbes including spores; disinfection - kills pathogens but not reliably spores.
• Autoclave - 121 °C, 15 psi, 15–20 min; moist heat coagulates protein and is the hospital standard.
• Hot-air oven - 160 °C for 2 h (dry heat), for glass, powders and oils; boiling is only disinfection.
• Biological indicator - *Geobacillus stearothermophilus* spores are the only true proof that an autoclave cycle was lethal.
• Gram-positive - retain crystal violet (thick peptidoglycan); Gram-negative - decolourise, take safranin, carry endotoxin (LPS).
• Acid-fast - mycolic acid resists acid decolourisation; ZN stain shows *M. tuberculosis* red on blue.
• Chain of infection - agent, reservoir, exit, transmission, entry, susceptible host; hand hygiene breaks the easiest link.
• Standard precautions - applied to every patient; transmission-based precautions (contact, droplet, airborne) are added on top.
• WHO 5 moments - before patient, before aseptic task, after fluid exposure, after patient, after surroundings; rub 20–30 s, wash 40–60 s.
• Airborne precautions - N95 plus a negative-pressure/well-ventilated room for TB, measles and varicella; a surgical mask is not enough.
• PPE doffing - gloves first, mask last; most contaminated item removed first.
• Significant bacteriuria - ≥10⁵ CFU/mL of a single organism in a clean-catch midstream urine.
• Blood culture - 2 sets from 2 sites before antibiotics; never refrigerate CSF or blood culture bottles.
• Active immunity - slow, long-lasting, has memory; passive immunity - immediate, short-lived, no memory.
• IgM - recent infection, does not cross the placenta; IgG - crosses the placenta and gives newborn protection.
• Type IV hypersensitivity - delayed, cell-mediated, read at 48–72 h (Mantoux); Type I is IgE anaphylaxis.
• BMW Rules 2016 - yellow (incinerate), red (autoclave and recycle plastic), white (sharps), blue (glass and metal implants).
• Needle-stick - wash, do not squeeze, report, test, start HIV PEP as early as possible within 72 h for 28 days.
• Cold chain - +2 to +8 °C; never freeze TT/Td, hepatitis B or PCV; VVM stage 3 or 4 means discard.
• AMR - ESBL, MRSA, CRE/NDM-1 and MDR-TB arise from misuse; countered by culture-guided therapy and stewardship.

Formulas and examples

• Bacterial growth: 500 *E. coli* per mL are incubated for 4 hours; generation time is 20 minutes.
  • n = 240 min / 20 min = 12 generations; 2¹² = 4,096.
  • N = 500 × 4,096 = 2,048,000 cells/mL (about 2.05 × 10⁶). This is why a specimen left on the bedside for hours gives a falsely high count.
• Urine colony count: 0.01 mL of a 1:100 diluted urine is plated and 48 colonies grow.
  • CFU/mL = (48 × 100) / 0.01 = 4,800 / 0.01 = 4.8 × 10⁵ CFU/mL — above 10⁵, so significant bacteriuria; report with the organism and sensitivity.
• Hypochlorite dilution for a blood spill: 1% hypochlorite is needed; available stock is 5% sodium hypochlorite; 2 litres (2,000 mL) of working solution required.
  • V₁ = (1 × 2,000) / 5 = 400 mL of stock, made up to 2,000 mL with water (so 400 mL stock + 1,600 mL water). Prepare fresh daily — hypochlorite loses strength on standing and in light.
• CAUTI rate: an ICU recorded 6 catheter-associated UTIs over 1,500 catheter days in a quarter.
  • Rate = (6 / 1,500) × 1,000 = 4.0 per 1,000 catheter days. If the next quarter has 3 infections in 1,250 catheter days, rate = 2.4 per 1,000 catheter days — a 40% fall, the kind of figure an HICC reports at a NABH audit.
• Hand-hygiene audit: a nurse was observed at 150 hand-hygiene opportunities and complied 108 times.
  • Compliance = (108 / 150) × 100 = 72% — below the 80%+ target most hospital infection-control programmes set; the audit then identifies which of the 5 moments was missed (usually moment 1 and moment 5).

Where it is used

• Hospital infection control: infection-control nurse roles in NABH/JCI-accredited chains (Apollo, Fortis, Manipal, Max, AIIMS and state medical colleges) — surveillance, hand-hygiene audits, outbreak investigation, antibiotic stewardship.
• CSSD and operation theatre: autoclave loading and cycle validation, Bowie–Dick and biological indicator testing, sterile pack shelf life, OT discipline and fumigation records — a common first posting and a frequent interview topic.
• Community health and national programmes: cold-chain handling and UIP sessions at PHC/sub-centre, DOT under NTEP, ICTC counselling under NACP, source reduction and larval surveys under NVBDCP, outbreak reporting through IHIP/IDSP.
• Laboratory and diagnostics: specimen collection and transport, assisting with CBNAAT, rapid antigen and ELISA testing in hospital and NABL-accredited labs; phlebotomy and sample-integrity checks.
• Dialysis, ICU, NICU and oncology units: device bundles, protective isolation of neutropenic patients, water and machine disinfection in dialysis, milk-handling and hand hygiene in NICU.
• Industry and regulation: clinical research coordination, pharmaceutical and vaccine-plant quality roles, waste-management vendors and SPCB compliance, medical-device sterilisation services, nurse educator posts teaching the first-year Microbiology paper.

Interview questions

• Q: What is the difference between sterilisation and disinfection? A: Sterilisation destroys all micro-organisms including bacterial spores; disinfection destroys most pathogens on inanimate objects but does not reliably kill spores.
• Q: State the autoclave parameters and why moist heat beats dry heat. A: 121 °C at 15 psi for 15–20 minutes (or 134 °C at 30 psi for 3–4 minutes); moist heat coagulates protein and steam carries far more latent heat, so it kills faster at a lower temperature than dry air.
• Q: How would you prove that an autoclave cycle actually sterilised the load? A: By a biological indicator — *Geobacillus stearothermophilus* spore strip showing no growth; chemical tape and the printout only confirm exposure, not lethality.
• Q: Name the WHO 5 moments of hand hygiene. A: Before touching a patient, before a clean/aseptic procedure, after body-fluid exposure risk, after touching a patient, and after touching the patient's surroundings.
• Q: When is handwashing with soap and water compulsory instead of alcohol rub? A: When hands are visibly soiled, after using the toilet, and with spore-formers such as *Clostridioides difficile* or *Bacillus anthracis*, because alcohol does not kill spores.
• Q: A patient has sputum-positive pulmonary TB. What precautions do you take? A: Airborne precautions — N95 respirator, a negative-pressure or well-ventilated single room with the door closed, patient in a surgical mask during transport, cough etiquette, and treatment with notification under NTEP.
• Q: What is the correct order of removing PPE? A: Gloves, then goggles/face shield, then gown, and the mask or respirator last, outside the room, with hand hygiene between steps.
• Q: You get a needle-stick injury from an HIV-positive patient. What do you do? A: Wash with soap and running water without squeezing, report immediately, get baseline testing, and start three-drug post-exposure prophylaxis as early as possible — within 72 hours — continued for 28 days, with follow-up tests.
• Q: Explain the BMW 2016 colour coding with one example each. A: Yellow for anatomical and soiled waste (incineration), red for contaminated recyclable plastic such as IV sets (autoclave then shred), white puncture-proof for sharps such as needles, blue for broken glass vials and metal implants.
• Q: Why must blood cultures be taken before antibiotics and from two sites? A: Antibiotics suppress bacterial growth and give false negatives; two sets from two sites help distinguish true bacteraemia from skin contamination.
• Q: Difference between active and passive immunity? A: Active immunity follows infection or vaccination — slow to develop but long lasting with memory; passive immunity is ready-made antibody (maternal or immunoglobulin) — immediate but short lived with no memory.
• Q: What is MRSA and how is it managed on the ward? A: *Staphylococcus aureus* resistant to methicillin and other beta-lactams; managed with contact precautions, dedicated equipment, decolonisation where indicated, and glycopeptides such as vancomycin guided by culture.
• Q: How is dengue different from malaria in terms of vector and prevention? A: Dengue spreads through the day-biting *Aedes aegypti* breeding in clean stored water — controlled by source reduction; malaria spreads through night-biting *Anopheles* — controlled by insecticide-treated nets and residual spraying.

Common mistakes

• Writing "sterilisation" where "disinfection" is correct (boiling, hypochlorite and alcohol disinfect; they do not sterilise).
• Quoting 121 °C with 30 psi or 134 °C with 15 psi — the temperature, pressure and time must be paired correctly.
• Skipping cleaning: sterilising a blood-soiled instrument, or using a disinfectant on an unwashed surface, where organic matter inactivates it.
• Confusing a surgical mask with an N95, or using droplet precautions for an airborne disease such as TB or measles.
• Reversing immunoglobulin facts — saying IgM crosses the placenta, or that IgG indicates acute recent infection.
• Mixing up colour bins: putting needles in the red bag, or plastic IV sets in yellow — a direct BMW Rules 2016 violation picked up in audits.
• Sending a specimen without the date, time and site, collecting urine from the catheter bag, refrigerating CSF, or starting antibiotics before the culture is drawn.
• Squeezing a needle-stick wound or applying bleach/iodine into it, and delaying the exposure report beyond the PEP window.
• Dilution errors — using 5% hypochlorite neat for a surface, or a stale solution prepared days earlier.

Related topics

Anatomy and physiology essentials · Pharmacology for nurses · Nutrition and dietetics · Community health nursing and national health programmes · Fundamentals of nursing: asepsis and procedures · Medical-surgical nursing: communicable diseases