FMGE Microbiology Syllabus

How is Staphylococcus aureus distinguished from coagulase-negative staphylococci?

S. aureus is coagulase-positive (clots plasma via coagulase enzyme) and usually ferments mannitol (yellow on MSA). Coagulase-negative staphylococci (e.g., S. epidermidis, S. saprophyticus) are coagulase-negative.

What is the basis of Lancefield grouping, and how are streptococci classified by hemolysis?

Lancefield grouping is based on cell wall carbohydrate antigens (groups A-U). Hemolysis: alpha (partial, green - S. pneumoniae, viridans), beta (complete clearing - S. pyogenes group A), gamma (none - enterococci).

How is Streptococcus pneumoniae differentiated from viridans streptococci (both alpha-hemolytic)?

S. pneumoniae is optochin-sensitive and bile-soluble; viridans streptococci are optochin-resistant and bile-insoluble. S. pneumoniae shows lancet-shaped diplococci with a capsule.

What are the key spore-forming gram-positive bacilli and a disease caused by each?

Bacillus anthracis (anthrax), Clostridium tetani (tetanus), Clostridium botulinum (botulism), Clostridium perfringens (gas gangrene), Clostridium difficile (pseudomembranous colitis).

What biochemical test pattern (IMViC) identifies Escherichia coli?

IMViC = Indole +, Methyl Red +, Voges-Proskauer -, Citrate - (i.e., ++--). This distinguishes E. coli from Enterobacter/Klebsiella (which are --++).

Which member of Enterobacteriaceae produces H2S, is motile, and is a non-lactose fermenter causing enteric fever?

Salmonella Typhi (causes typhoid/enteric fever). It is a motile, non-lactose-fermenting, H2S-producing gram-negative bacillus identified on TSI and detected serologically by the Widal test.

What characteristic 'swarming' growth and which urease/H2S features identify Proteus?

Proteus shows swarming motility on non-selective agar (concentric waves). It is strongly urease-positive, H2S-positive, and non-lactose fermenting. Anti-Proteus OX antigens are used in the Weil-Felix test for rickettsiae.

Which gram-negative organism is oxidase-positive, produces blue-green pigment, and has a grape-like odor?

Pseudomonas aeruginosa. It is oxidase-positive, a non-lactose fermenter, produces pyocyanin (blue-green) and pyoverdin pigments, has a fruity/grape-like odor, and is a major nosocomial/MDR pathogen.

What is the principle and reading of the Triple Sugar Iron (TSI) agar test?

TSI contains glucose, lactose, sucrose, plus iron salts. Slant/butt color shows acid (yellow) or alkaline (red) fermentation; gas = cracks; H2S = black precipitate. E.g., Salmonella = K/A (red slant, yellow butt) with H2S and gas.

Compare the cell-wall structure of Mycobacteria with typical gram-positive bacteria.

Mycobacteria have a peptidoglycan layer covalently linked to arabinogalactan and a thick outer layer of mycolic acids (waxy), making them acid-fast, slow-growing, and resistant to drying and many disinfectants — unlike ordinary gram-positives.

Which spirochete causes syphilis, and what serological tests are used (non-treponemal vs treponemal)?

Treponema pallidum. Non-treponemal (screening): VDRL and RPR (detect reagin antibody). Treponemal (confirmatory): TPHA, FTA-ABS (detect specific antibody).

Name the spirochete causing leptospirosis and its classic mode of transmission.

Leptospira interrogans. Transmitted through contact with water/soil contaminated by rodent (rat) urine; presents as Weil's disease (jaundice, renal failure, hemorrhage). Diagnosed by MAT (microscopic agglutination test).

What culture conditions are required for obligate anaerobes, and name two common anaerobic pathogens.

Obligate anaerobes require an oxygen-free environment (anaerobic jar with GasPak, thioglycollate broth). Examples: Clostridium species, Bacteroides fragilis, Fusobacterium, Actinomyces.

List three zoonotic bacterial infections and their animal reservoirs.

Brucellosis (Brucella - cattle/goats/pigs), Plague (Yersinia pestis - rodents via fleas), Anthrax (Bacillus anthracis - herbivores/cattle), Leptospirosis (rodents).

What is the gold-standard confirmatory diagnostic for tuberculosis, and what rapid molecular test is widely used?

Culture on solid (LJ) or liquid (MGIT) media is the gold standard. CBNAAT/GeneXpert MTB/RIF is the rapid molecular test that detects M. tuberculosis DNA and rifampicin resistance within hours.

What is the difference between a screening test and a confirmatory test in serological diagnosis?

Screening tests have high sensitivity (few false negatives) to detect all possible positives (e.g., ELISA, VDRL). Confirmatory tests have high specificity (few false positives) to verify true positives (e.g., Western blot, TPHA).

Classify medically important DNA viruses by their families.

Herpesviridae (HSV, VZV, CMV, EBV), Hepadnaviridae (HBV), Adenoviridae, Papillomaviridae (HPV), Poxviridae (smallpox), Parvoviridae (B19), Polyomaviridae. Most are double-stranded DNA (parvovirus is ssDNA).

Which DNA virus establishes latency in dorsal root ganglia and causes both chickenpox and shingles?

Varicella-zoster virus (VZV, HHV-3). Primary infection causes chickenpox (varicella); reactivation from dorsal root/sensory ganglia causes shingles (herpes zoster).

Name the medically important RNA viruses causing influenza, polio, rabies, and dengue.

Influenza: Orthomyxovirus. Polio: Enterovirus (Picornaviridae). Rabies: Lyssavirus (Rhabdoviridae, bullet-shaped). Dengue: Flavivirus (arbovirus, Aedes mosquito).

What is antigenic drift versus antigenic shift in influenza virus?

Antigenic drift: minor point mutations in HA/NA causing seasonal epidemics. Antigenic shift: major reassortment of gene segments producing a new subtype, causing pandemics. Only influenza A undergoes shift.

Compare the transmission routes of Hepatitis A, B, C, and E viruses.

HAV and HEV: feco-oral (enteral, water-borne). HBV: parenteral, sexual, perinatal. HCV: parenteral/blood-borne. HEV is dangerous in pregnancy (high mortality); HBV and HCV cause chronic infection/cirrhosis/HCC.

What does the presence of HBsAg, anti-HBs, and HBeAg each indicate in hepatitis B serology?

HBsAg: active/current HBV infection. Anti-HBs: immunity (recovery or vaccination). HBeAg: high viral replication and infectivity. IgM anti-HBc indicates recent/acute infection.

What is the structure and key target cell of HIV, and which test confirms infection?

HIV is an enveloped retrovirus (two ssRNA copies, reverse transcriptase) that targets CD4+ T lymphocytes (via gp120/CCR5/CXCR4). Screening: ELISA; confirmation: Western blot or HIV RNA viral load.

Classify medically important fungi by morphology with an example of each.

Yeasts (Candida, Cryptococcus), Molds/filamentous (Aspergillus, dermatophytes), and Dimorphic fungi (Histoplasma, Blastomyces, Coccidioides, Sporothrix - mold at 25°C, yeast at 37°C).

What stain demonstrates Cryptococcus neoformans in CSF, and what is its diagnostic feature?

India ink (negative stain) shows the thick polysaccharide capsule as a clear halo around budding yeast. The cryptococcal capsular antigen (CrAg) latex test is also highly sensitive/specific.

Differentiate Plasmodium falciparum from P. vivax malaria on key features.

P. falciparum: multiple ring forms, banana-shaped gametocytes, no Schuffner's dots, causes cerebral/severe malaria, all-stage RBC infection. P. vivax: amoeboid trophozoites, Schuffner's dots, relapses (hypnozoites), prefers reticulocytes.

Compare the transmission and diagnostic stool finding for Entamoeba histolytica versus Giardia lamblia.

Both are feco-oral protozoa. E. histolytica: causes amoebic dysentery/liver abscess; stool shows trophozoites with ingested RBCs or quadrinucleate cysts. Giardia: causes malabsorption/steatorrhea; stool shows pear-shaped trophozoites and oval 4-nuclei cysts.

What is the recommended specimen for diagnosing pinworm (Enterobius vermicularis) infection, and why?

The cellophane/Scotch tape (NIH swab) test applied to the perianal skin in the early morning, because the female worm deposits eggs on the perianal region at night rather than in stool.

What are the main methods of antimicrobial susceptibility testing, and what does MIC stand for?

Kirby-Bauer disk diffusion (measures zone of inhibition), broth/agar dilution, and E-test (gradient strip). MIC = Minimum Inhibitory Concentration, the lowest antibiotic concentration that visibly inhibits bacterial growth.

List key principles of specimen collection and transport for microbiology.

Collect before starting antibiotics, from the actual site of infection using aseptic technique, in adequate quantity, in sterile/appropriate containers, label correctly, and transport promptly (or use transport media like Stuart's/Cary-Blair/VTM) to maintain organism viability.