Infections, Mycology, molecular biology, bacterial culture Flashcards
(13 cards)
What are HAIs, and what distinguishes endogenous vs. exogenous infections?
HAIs: Infections acquired during medical care (e.g., hospitals).
Endogenous: Caused by the patient’s own microbiota (e.g., Candida albicans).
Exogenous: From external sources (e.g., Aspergillus fumigatus spores).
Describe key features of S. aureus relevant to HAIs.
Gram-positive cocci in clusters.
Catalase-positive, β-hemolytic on blood agar.
Virulence factors: MSCRAMMs (adhesion), Protein A (immune evasion), TSST-1 (toxic shock).
How does S. aureus become methicillin-resistant?
Acquires mecA gene via SCCmec cassette.
Encodes PBP2a with low β-lactam affinity.
Resistant to all β-lactams (penicillin’s, cephalosporins).
How does C. difficile cause disease, and how is it diagnosed?
Toxins A/B damage intestinal epithelium → watery diarrhea.
Diagnosis: PCR for toxin genes in stool; SAB agar cultures (gray, non-hemolytic colonies).
Name 3 strategies to prevent HAIs.
Sterilize equipment (autoclaving).
Hand hygiene (WHO 5-step technique).
Screening (e.g., MRSA nasal swabs pre-surgery).
Mycology (Ascomycota Focus)
Compare Saccharomycotina and Pezizomycotina.
Saccharomycotina: Unicellular yeasts (e.g., Candida), asexual budding.
Pezizomycotina: Multicellular molds (e.g., Aspergillus), sexual ascospores in asci.
Candida albicans Infections
What are the clinical manifestations of C. albicans infections?
Oral thrush: White plaques in mouth (immunocompromised).
Vaginal thrush: Cottage cheese-like discharge.
Candidaemia: Bloodstream infection (fever, hypotension).
How does A. fumigatus cause disease?
Inhalation of spores → lung invasion (aspergillosis).
Risk factors: Immunosuppression, COPD.
Diagnosis: Sputum culture on SAB agar; galactomannan antigen test.
Name a dermatophyte and its associated infection.
Trichophyton rubrum: Causes athlete’s foot (scaly interdigital skin).
Diagnosis: KOH microscopy of skin scrapings; lactophenol cotton blue stain.
Give two industrial applications of Ascomycota.
Penicillin production: Penicillium chrysogenum.
Baking/brewing: Saccharomyces cerevisiae.
Selective vs. Differential Media Compare Mannitol Salt Agar (MSA) and MacConkey Agar.
MSA: Selective (7.5% NaCl) + differential (mannitol fermentation → yellow).
MacConkey: Selective (bile salts) + differential (lactose fermentation → pink).
Define α, β, and γ hemolysis.
α: Partial (greenish zone; Streptococcus pneumoniae).
β: Complete (clear zone; Streptococcus pyogenes).
γ: None (no change; Enterococcus faecalis).
How does MALDI-TOF identify bacteria?
