Microbiology
High-yield MBBS Microbiology question bank — bacteriology, immunology, virology, mycology and parasitology, with laboratory diagnosis, at Ananthanarayan & Paniker / Jawetz depth.
12chapters144questions82High-Yield
Definition
Influenza virus is an enveloped RNA orthomyxovirus with segmented genome, causing seasonal epidemics and periodic pandemics.
Structure
- Single-stranded RNA in 8 segments, helical symmetry
- Envelope with haemagglutinin (H) — attachment
- Neuraminidase (N) — release of virions
- Types A (pandemics), B (epidemics), C (mild)
Antigenic Variation
- Antigenic drift — minor point mutations → epidemics
- Antigenic shift — major genetic reassortment → pandemics (type A only)
- Reassortment possible because the genome is segmented
H attaches the virus and N releases new virions from infected cells. Change Mechanism Result Drift Point mutation Epidemic Shift Reassortment Pandemic Applied
- Treatment: oseltamivir (neuraminidase inhibitor)
- Vaccine reformulated annually because of antigenic drift
🔑KEY POINTS TO REMEMBER- Influenza: segmented RNA virus with H and N surface antigens.
- Antigenic drift → epidemics; antigenic shift → pandemics (type A).
- Oseltamivir for treatment; annual vaccine needed.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Hepatitis viruses (A to E) are unrelated viruses sharing a tropism for the liver, differing in transmission and outcome.
Faeco-Oral (enteric) Route
- Hepatitis A — RNA, no chronicity, vaccine available
- Hepatitis E — RNA, no chronicity, high mortality in pregnancy
- Both cause water-borne epidemics
Parenteral / Sexual Route
- Hepatitis B — DNA virus, chronicity, cirrhosis, hepatocellular carcinoma; vaccine available
- Hepatitis C — RNA, high chronicity, no vaccine, curable with antivirals
- Hepatitis D — defective, needs HBsAg coat
Route of spread predicts whether chronic liver disease follows. Virus Route Chronicity A Faeco-oral No B Parenteral Yes C Parenteral High E Faeco-oral No (severe in pregnancy) Applied
- Vaccines available for A and B only
- Hepatitis C now curable with direct-acting antivirals
🔑KEY POINTS TO REMEMBER- A and E spread faeco-orally and do not become chronic.
- B, C and D are blood-borne and cause chronic liver disease.
- Hepatitis E carries high mortality in pregnancy.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Hepatitis B virus (HBV) is a DNA hepadnavirus transmitted parenterally, sexually and vertically, causing acute and chronic hepatitis.
Structure & Antigens
- Dane particle — complete infectious virion
- HBsAg — surface antigen; marker of infection
- HBcAg — core antigen (not detected in blood)
- HBeAg — marker of high infectivity and active replication
Serological Markers
- HBsAg positive → current infection (>6 months = chronic)
- Anti-HBs → immunity (recovery or vaccination)
- IgM anti-HBc → recent/acute infection; useful in the window period
- HBV DNA → viral load, monitors therapy
Marker patterns distinguish acute infection, recovery and chronic carriage. Marker Meaning HBsAg Current infection Anti-HBs Immunity HBeAg High infectivity Applied
- Vaccine contains HBsAg (recombinant) → anti-HBs only
- Complications: cirrhosis and hepatocellular carcinoma
🔑KEY POINTS TO REMEMBER- HBV is a DNA virus; the Dane particle is the complete virion.
- HBsAg = infection, anti-HBs = immunity, HBeAg = high infectivity.
- Chronic infection leads to cirrhosis and hepatocellular carcinoma.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
HIV is a retrovirus that destroys CD4 T lymphocytes, causing progressive immunodeficiency culminating in AIDS.
Virus & Transmission
- Enveloped RNA retrovirus with reverse transcriptase
- HIV-1 (worldwide) and HIV-2 (West Africa, milder)
- Binds CD4 receptor plus CCR5/CXCR4 coreceptors
- Spread: sexual, blood, vertical (mother to child)
Course & Diagnosis
- Acute seroconversion illness → long asymptomatic phase → AIDS
- AIDS: CD4 <200/μL or an AIDS-defining illness
- Opportunistic infections: tuberculosis, Pneumocystis, candidiasis, cryptococcosis; Kaposi sarcoma
- Diagnosis: ELISA screening → confirmation; p24 antigen and PCR in the window period
Progressive CD4 destruction opens the door to opportunistic infection. Marker Use ELISA Screening p24 antigen Window period CD4 count Monitoring Applied
- Treatment: lifelong combination antiretroviral therapy
- Prevention of mother-to-child transmission with antiretrovirals
🔑KEY POINTS TO REMEMBER- HIV is a retrovirus targeting CD4 cells via reverse transcriptase.
- AIDS defined by CD4 <200/μL or AIDS-defining illness.
- ELISA screening; treated with lifelong combination antiretroviral therapy.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Rabies is a fatal viral encephalitis caused by a bullet-shaped RNA rhabdovirus, transmitted by the bite of an infected animal.
Virus & Pathogenesis
- Bullet-shaped enveloped RNA virus
- Enters through a bite; replicates in muscle
- Travels along peripheral nerves to the CNS
- Negri bodies — cytoplasmic inclusions in hippocampus and cerebellum
- Incubation 1–3 months (varies with bite site)
Clinical Features & Prophylaxis
- Prodrome → hydrophobia, aerophobia, hyperexcitability, spasms
- Paralytic (dumb) form less common; almost 100% fatal once symptoms begin
- Post-exposure prophylaxis: wound washing with soap and water, rabies vaccine, plus immunoglobulin for category III bites
- Pre-exposure vaccination for high-risk groups
Neural spread explains the long, variable incubation period. Element Detail Shape Bullet-shaped Inclusion Negri body Outcome Nearly always fatal Applied
- Prophylaxis is fully effective if started promptly
- Wound washing alone markedly reduces risk
🔑KEY POINTS TO REMEMBER- Rabies is a bullet-shaped RNA virus spreading along nerves to the CNS.
- Negri bodies are diagnostic; hydrophobia is characteristic.
- Almost always fatal — prevention by prompt post-exposure prophylaxis.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Poliomyelitis is an enteroviral infection that may destroy anterior horn cells, causing acute flaccid paralysis.
Virus & Spread
- Poliovirus — naked RNA enterovirus, three serotypes (1, 2, 3)
- Faeco-oral transmission
- Multiplies in gut lymphoid tissue → viraemia → CNS
- Most infections are asymptomatic or minor; <1% develop paralysis
Paralysis & Vaccines
- Asymmetrical flaccid paralysis, lower limbs, no sensory loss
- OPV (Sabin) — live, oral, gives gut immunity, aids herd immunity; rare vaccine-associated paralysis
- IPV (Salk) — killed, injectable, very safe, no gut immunity
- Global eradication programme with acute flaccid paralysis surveillance
Only a small minority of infections reach the anterior horn cells. Vaccine Type Gut immunity OPV Live oral Yes IPV Killed No Applied
- Pulse polio immunisation campaigns
- India certified polio-free in 2014
🔑KEY POINTS TO REMEMBER- Poliovirus spreads faeco-orally and destroys anterior horn cells.
- Causes asymmetrical flaccid paralysis without sensory loss.
- OPV gives gut immunity; IPV is killed and safest.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Measles is a highly contagious paramyxovirus infection causing fever, respiratory symptoms and a characteristic rash.
Clinical Features
- Enveloped RNA paramyxovirus; droplet spread; incubation ~10 days
- Prodrome — fever, cough, coryza, conjunctivitis (3 C’s)
- Koplik spots on buccal mucosa — pathognomonic
- Maculopapular rash starting behind the ears, spreading downwards
- Rash fades with branny desquamation
Complications & Prevention
- Otitis media, bronchopneumonia (commonest cause of death), diarrhoea
- Post-measles encephalitis; SSPE (subacute sclerosing panencephalitis) years later
- Vitamin A deficiency worsens outcome
- Live attenuated vaccine (MR/MMR) at 9 and 15–18 months
Koplik spots appear before the rash, allowing early diagnosis. Feature Detail Pathognomonic sign Koplik spots Commonest fatal complication Pneumonia Late complication SSPE Applied
- Vitamin A reduces measles mortality
- Measles elimination is a global target
🔑KEY POINTS TO REMEMBER- Measles: paramyxovirus with fever, 3 C’s and Koplik spots.
- Rash spreads downwards and desquamates.
- Pneumonia is the commonest fatal complication; SSPE is a late sequel.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Dengue is a mosquito-borne flavivirus infection transmitted by Aedes aegypti, with four serotypes.
Virus & Transmission
- RNA flavivirus, serotypes DEN 1–4
- Vector: Aedes aegypti — day-biting, breeds in clean stored water
- Infection gives lifelong immunity to that serotype only
- Secondary infection with a different serotype → severe dengue (antibody-dependent enhancement)
Clinical Forms & Diagnosis
- Dengue fever — high fever, severe retro-orbital headache, break-bone myalgia, rash
- Dengue haemorrhagic fever — plasma leakage, thrombocytopenia, positive tourniquet test
- Dengue shock syndrome — circulatory failure
- Diagnosis: NS1 antigen (early), IgM ELISA, RT-PCR
Plasma leakage rather than bleeding drives the severe forms. Test Timing NS1 antigen Day 1–5 IgM ELISA After day 5 Applied
- Treatment is supportive — fluids; avoid aspirin and NSAIDs
- Vector control is the mainstay of prevention
🔑KEY POINTS TO REMEMBER- Dengue: flavivirus with 4 serotypes, spread by day-biting Aedes aegypti.
- Secondary infection with another serotype risks haemorrhagic fever.
- NS1 antigen early, IgM later; treat with fluids, avoid NSAIDs.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Rubella is a mild togavirus infection of children, but is seriously teratogenic in early pregnancy.
Postnatal Rubella
- RNA togavirus, droplet spread
- Mild fever with fine maculopapular rash
- Posterior auricular and suboccipital lymphadenopathy — characteristic
- Arthralgia common in adults; usually self-limiting
Congenital Rubella Syndrome
- Greatest risk in the first trimester
- Classic triad: cataract, congenital heart disease (PDA), deafness
- Also microcephaly, intellectual disability, ‘blueberry muffin’ rash
- Diagnosis: IgM antibody in the infant
Infection during organogenesis produces the classic triad of defects. Feature Detail Triad Cataract, PDA, deafness Highest risk First trimester Prevention MMR vaccine Applied
- MMR vaccination of girls prevents congenital rubella syndrome
- Live vaccine — avoid in pregnancy
🔑KEY POINTS TO REMEMBER- Rubella is mild postnatally but teratogenic in the first trimester.
- Congenital triad: cataract, patent ductus arteriosus, deafness.
- Prevented by MMR vaccine, which is contraindicated in pregnancy.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Mumps is an acute paramyxovirus infection characterised by painful swelling of the parotid glands.
Features
- Enveloped RNA paramyxovirus; droplet spread
- Incubation 16–18 days
- Bilateral parotitis — painful, pushes ear lobe up and out
- Fever, malaise; ↑ serum amylase
- Infectious from before to after the swelling appears
Complications & Prevention
- Orchitis in post-pubertal males (may cause subfertility)
- Aseptic meningitis (commonest CNS complication), encephalitis
- Pancreatitis, oophoritis, deafness
- Prevented by MMR live attenuated vaccine
Viraemia spreads the virus from the airway to glandular tissue. Complication Group Orchitis Post-pubertal males Aseptic meningitis Any Pancreatitis Any Applied
- Commonest cause of parotitis in children
- Treatment is symptomatic
🔑KEY POINTS TO REMEMBER- Mumps is a paramyxovirus causing bilateral painful parotitis.
- Complications: orchitis, aseptic meningitis, pancreatitis.
- Prevented by the MMR vaccine.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Rotavirus is the commonest cause of severe dehydrating diarrhoea in infants worldwide.
Virus & Pathogenesis
- Naked double-stranded RNA virus, wheel-shaped on electron microscopy
- Faeco-oral spread; very low infective dose
- Infects villous enterocytes of the small intestine
- Villous damage → lactase deficiency, osmotic diarrhoea; NSP4 acts as an enterotoxin
Clinical Features & Prevention
- Vomiting followed by profuse watery non-bloody diarrhoea
- Fever; rapid dehydration in infants 6–24 months
- Diagnosis: ELISA for antigen in stool
- Treatment: ORS and zinc; rotavirus vaccine (oral, live) in the immunisation schedule
Villous damage and a viral enterotoxin together produce watery diarrhoea. Feature Detail Appearance Wheel-shaped Stool Watery, non-bloody Prevention Oral vaccine Applied
- Leading vaccine-preventable cause of childhood diarrhoeal death
- ORS remains the mainstay of treatment
🔑KEY POINTS TO REMEMBER- Rotavirus: naked wheel-shaped dsRNA virus, faeco-oral spread.
- Commonest cause of severe infantile watery diarrhoea.
- Managed with ORS and zinc; prevented by oral rotavirus vaccine.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).Definition
Coronaviruses are enveloped RNA viruses with club-shaped surface spikes giving a crown-like appearance, causing respiratory illness.
Virus & Members
- Single-stranded RNA, enveloped, spike (S) protein forms the crown
- Common human coronaviruses — mild upper respiratory infection (common cold)
- SARS-CoV (2002), MERS-CoV (2012), SARS-CoV-2 (COVID-19)
- Zoonotic origin (bats and intermediate hosts)
Transmission & Diagnosis
- Droplet and aerosol spread; also contact with contaminated surfaces
- Features: fever, cough, breathlessness, loss of smell/taste; pneumonia and ARDS in severe cases
- Diagnosis: RT-PCR (standard), rapid antigen test
- Prevention: masks, hand hygiene, distancing, vaccination
The spike protein determines entry and is the main vaccine target. Virus Year Note SARS-CoV 2002 High mortality MERS-CoV 2012 Camel-linked SARS-CoV-2 2019 Pandemic Applied
- Spike protein is the target of most COVID-19 vaccines
- Enveloped → easily inactivated by soap and alcohol
🔑KEY POINTS TO REMEMBER- Coronaviruses are enveloped RNA viruses with crown-like spike proteins.
- SARS, MERS and COVID-19 are zoonotic and spread by droplets.
- RT-PCR for diagnosis; spike protein is the vaccine target.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Microbiology (Baveja).