Microbiology: Bacterial and Viral Pathogens

Bacterial Toxins and Pathogens

• Endotoxins: Characteristic of Gram-negative bacteria, heat-stable, part of the outer membrane, and induce immune system responses (typically not suppression).
• Exotoxins: Produced by both Gram-positive and Gram-negative bacteria, heat-labile, secreted, have specific antigenic properties, and contribute to various disease processes.
• Necrotizing fasciitis: Commonly associated with Streptococcus pyogenes. Staphylococcus aureus, Clostridium perfringens, Escherichia coli, and Pseudomonas aeruginosa can also be involved.
• Tuberculosis: Caused by Mycobacterium tuberculosis.
• Gram-positive bacteria: Characterised by a thick peptidoglycan layer and lack of an outer membrane.
• Gram-negative bacteria: Characterised by a thin peptidoglycan layer and an outer membrane with lipopolysaccharide (LPS).

Viral Pathogens and Infections

• Cervical cancer: Primarily associated with Human papillomavirus (HPV).
• Measles: Characterised by a maculopapular rash. Other symptoms may include a fever and sore throat.
• Common cold: Primarily caused by rhinoviruses. Adenoviruses, coronaviruses, and respiratory syncytial viruses are other possibilities.
• HIV: Primarily transmitted through blood and bodily fluids.
• Malaria: Transmitted by mosquitoes.
• Lyme disease: Associated with Borrelia burgdorferi and a distinctive "bull's-eye" rash.
• Diphtheria: Caused by Corynebacterium diphtheriae.
• Influenza: Influenza A viruses have key proteins (hemagglutinin [binds to host cells] and neuraminidase [releases viral particles]) that play critical roles in infection. Protein M2 plays a role in the acidification of the virus for uncoating.

Other Microbiological Concepts and Diseases

• Streptococcus pneumoniae: A common virulence factor is a capsule.
• Tetanus: Caused by a toxin produced by Clostridium tetani.
• Foodborne illness (poultry): Often caused by Salmonella enterica.
• Urinary tract infections (UTIs): Commonly associated with Escherichia coli.
• Hospital-acquired infections (HAIs): Staphylococcus aureus, Clostridium difficile, and Klebsiella pneumoniae and Pseudomonas aeruginosa are significant contributors.
• Bacterial superantigens: These molecules lead to exaggerated immune responses.
• Meningitis: Neisseria meningitidis is a causative agent that is linked to sepsis.
• Congenital birth defects: Rubella virus infection in pregnant individuals can cause birth defects.
• Gastric ulcers: Helicobacter pylori is a significant factor.
• Fungal infections (immunocompromised individuals): Candidiasis, aspergillosis, histoplasmosis, and cryptococcosis occur frequently.
• Bacterial endospores: Clostridium botulinum, Clostridium tetani and others produce endospores, allowing them to survive harsh conditions.
• Viruses: Cannot reproduce outside of a host cell, contain either RNA or DNA, lack typical cell structures, and have unique methods for entry into a host cell (e.g., endocytosis, fusion, direct injection).

Antimicrobial Mechanisms and Diagnostics

• Folic Acid Pathway: Sulfonamides inhibit PABA, a crucial step in dihydrofolic acid synthesis. Preventing this step interrupts the synthesis of nucleic acids, essential bacterial cofactors, for crucial metabolic functions, hindering bacterial growth.
• Quinolones: Inhibit DNA gyrase, a bacterial enzyme essential for DNA replication.
• TCBS Agar: Differential and selective medium used to isolate Vibrio cholerae from other bacteria.

Simplified Microbiology Concepts and Mnemonics

• Folic Acid Pathway: Sulfonamides inhibit PABA → Dihydrofolic acid synthesis (“Sulf-STOPs folic acid”).
• Mycobacterium tuberculosis: Causes TB in humans/animals. (“TB’s wall is thick (peptidoglycan) and complex”).
• AB Toxin (Vibrio cholerae): A subunit = Action (affects Gs protein, ↑cAMP); B subunit = Binding (“A = Action, B = Binding”).
• HIV-1 Protease: Cleaves Gag-Pol polyproteins for virus assembly (“Protease Cuts for Packaging”).
• Influenza A: M2: Acidifies interior for uncoating; Neuraminidase (NA): Releases progeny virions (“M2 = Acid Machine, NA = Viral Exit”).
• Virus Entry: Endocytosis, Fusion, Direct injection (“Viruses ENTER Easily”).
• Healthcare-Associated Infections (HCALs): Poor hygiene, invasive devices. Prevention: HAND CARE (H: Hand hygiene, A: Aseptic techniques, N: Need-based device use, D: Disinfect).

This quiz covers important concepts in microbiology, focusing on bacterial toxins such as endotoxins and exotoxins, as well as various pathogens like Streptococcus pyogenes and Mycobacterium tuberculosis. It also explores viral infections, including those associated with HPV and cervical cancer. Enhance your understanding of pathogens and their implications in human health.