Mega Revision of Microbiology for NEET PG 2023

Introduction

• Microbiology is a volatile subject that requires focused study on high-yield topics.
• The session will be image-based, covering key points in parasitology, bacteriology, virology, and fungi.

Part 1: Parasitology

Entamoeba histolytica

• Flask-shaped ulcer: Common in the cecum.
• Anchovy sauce appearance: Brownish pus in the liver.
• Trophozoites: One nucleus; cyst form has four nuclei (cartwheel appearance).
• Erythrophagocytosis: Trophozoite engulfs red blood cells.
• Chromatoid body: Composed of ribonucleoprotein (RNP).
• Treatment: Metronidazole plus paromomycin (luminal amoebicide).

Balantidium coli

• Ciliated protozoa: Largest protozoan invading the human intestine.
• Binucleated: Both cyst and trophozoite forms have two nuclei (one macronucleus and one micronucleus).
• Treatment: Tetracycline or metronidazole.

Giardia lamblia

• Trophozoite: Two nuclei, eight flagella (Falling Leaf motility).
• Luminal organism: Seen in the duodenal lumen.
• Treatment: Metronidazole or tinidazole.

Trichomonas vaginalis

• Only trophozoite form: No cyst form; causes strawberry cervix.
• Motility: Twitching motility.
• Media: Diamond media.

Trypanosoma cruzi

• C-shaped organism: Causes Chagas disease (Romana's sign: unilateral eye swelling).
• Chronic condition: Megaesophagus.
• Vector: Triatomine bug.

Trypanosoma brucei

• West African vs. East African sleeping sickness:
  • West African (gambiense) treated with pentamidine.
  • East African (rhodesiense) treated with suramin
• Winter bottom sign: Lymphadenopathy in West African sleeping sickness.

Leishmania

• Causes Kala-azar: Massive splenomegaly; diagnosed with rk39 antigen testing.
• LD bodies in macrophages: Large and small dot appearance.
• Treatment: Liposomal amphotericin B for Kala-azar.

Part 2: Bacteriology

General Points

• Gram-positive cocci: Most are gram-positive, except for Neisseria, Moraxella, and Veillonella.

Staphylococcus aureus

• Appearance: Grape-like clusters, golden pigment.
• Hemolysis: Narrow zone of beta-hemolysis.
• Catalase positive.
• Mannitol salt agar: Selective and differential, yellow color indicates mannitol fermentation.

Streptococcus Classification

• Alpha hemolytic: Streptococcus pneumoniae (bile soluble, optochin sensitive).
• Beta hemolytic:
  • Group A: Streptococcus pyogenes (bacitracin sensitive).
  • Group B: Streptococcus agalactiae (CAMP test positive).

Bacillus anthracis

• Malignant edema appearance: Necrotic, black hemorrhagic tissue.
• Boxcar appearance: Seen on Gram stain.
• Medusa head appearance: On nutrient agar.

Clostridium spp.

• C. tetani: Causes lockjaw, spastic muscle contractions.
• C. perfringens: Causes gas gangrene; stormy clot formation in litmus milk.
• C. difficile: Pseudomembranous enterocolitis; treated with vancomycin and metronidazole.

Part 3: Virology

DNA Viruses

• Hepatitis B: Only DNA hepatitis virus.
• Herpesviridae: Includes herpes simplex viruses and varicella-zoster.
• Adenoviridae: Causes respiratory infections.
• Poxviridae: Molluscum contagiosum – cup-shaped lesions with HP bodies.

RNA Viruses

• Rota virus: Double-stranded RNA; causes diarrhea in children.
• Influenza virus: Single-stranded segmented RNA.
• Picornaviruses: Include enteroviruses and hepatoviruses (A, E).

Key Inclusions and Stains

• Negri bodies: In rabies; seen in the hippocampus and cerebellum.
• Cowdry type A: Seen in herpes simplex virus (HSV).
• Downy cells: Associated with Epstein-Barr virus in infectious mononucleosis.

Conclusion

• This session covered high-yield topics in microbiology, focusing on key images and associated clinical points.
• The importance of revising these critical topics for exams is emphasized.
• Further revisions may include studying fungi and bullet points for quick recall.