M. bovis (TB complex) and M. kansasii cause TB-like respiratory illness in humans -- they are also INH-sensitive. Remember that M. avium-intracellulare and most other nontuberculous mycobacterium are INH-resistant.
Photochromogens (yellow-orange pigment in light): M. kansasii and M. marinum (swimming pool granuloma). It's sunny in Kansas, and over the ocean.
Scotochromogens (pigment in dark and in light): M. scrofulaceum (scrofula, granulomatous cervical lymphadenitis). It's dark where your scrotum is.
Nonchromogens (no pigment): M. avium-intracellulare.
-----------
Rapid death in stationary phase: Strep pneumo, Neisseria.
Klebsiella - butanediol; E. coli -- mixed acids (lactic, formic, acetic acids)
Both Mycoplasma and all fungi have sterols in their cell membranes.
Normal flora: Haemophilus influenza, Candida albicans,
-----------
Isoniazid is activated by catalase and inhibits cell wall synthesis by binding to an enoyl-acyl carrier protein reductase involved in mycolic acid synthesis. Isoniazid resistance is mediated by mutations that knock out catalase or the reductase.
Clavulanic acid is not effective against all beta lactamases, including Class I chromosomally encoded ones (Pseudomonas, Enterobacter, Citrobacter, Serratia).
Metronidazole: intrinsic resistance in Actinomyces; must be reduced to active toxic metabolites in the cell -- these damage DNA.
Quinolones: Both stepwise chromosomal (altered gyrase, reduced uptake) and plasmid-mediated resistance.
Streptomycin binds to single site (S12 protein) on 30S ribosome and is susceptible to single base pair change mutation. Other aminoglycosides bind to multiple sites and are less susceptible. Main mechanism of resistance to aminoglycosides, however, is plasmid- or chromosomally-encoded enzyme inactivation.
Tetracycline: increase efflux of drug (plasmid encoded), or modify ribosome (plasmid encoded).
No comments:
Post a Comment