Old Micro Stuff
Terms
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Clostridium spp.
Basic characteristics -
- Anaerobic, gram positive rod, "boxcar-shaped"
- Spore-former can survive hostile environments
- Soil - natural habitat
- Most rapidly growing organism (every 12 minutes) -
Clostridium dificile
Basic Characteristics -
- Disease: nosocomial diarrhea -> pseudomembranous colitis
- Predisposing factor = antimicrobial therapy
-Pathogenesis:
Toxin A - enterotoxin, more important
Toxin B - cytotoxin
- Treatment: metronidazole p.o. -
Clostridium dificile
Characteristics of Disease -
- Organism is obtained from hospital environment
- Gut flora is altered by antimicrobial therapy
- Alteration in gut flora reduces its capacity to inhibit the growth of C. difficile
- C. dificile grows and produces toxins in gut
- Toxin mediates diarrhea and more severe manifestations such as non-specific and pseudomembranous colitis -
Clostridium perfringens
Basic Characteristics -
- Disease: gas gangrene, food poisoning
- Normal bowel flora
- Predisposing factor = traumatic wound, post-surgery
- Virulence: histotoxic
- Treatment: debridement (amputation), leave wound open to air, Pen G -
Clostridium perfringens
Characteristics of Disease -
- Inoculation of tissue during trauma
- Tissue damage restricts blood flow and oxygenation of tissue
- Organism either germinates from spores introduced into wound or vegetative organisms begin to grow in tissue
- Very rapid growing organism
- Gas is a metabolic by-product
- Produces proteolytic and other toxins that degrade tissue
- There is no pus b/c WBC’s recruited by immune response are quickly degraded - Clostridium botulinum
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- Disease – flaccid paralysis leading to respiratory arrest
- Three forms of disease:
- Infant botulism - most common, honey/dirt ingestion, constipation, poor feeding, consume organism
- Food-borne botulism - improperly canned vegetables, soups, fish (home-canned), consume toxins
- Wound botulism organism in wound
- Inhalational – a bioterrorism agent
- Pathogenesis: neurotoxin - blocks Ach release -> flaccid paralysis -> difficulty swallowing, talking, suckling -> death by respiratory arrest
- Tx: respiratory support plus antitoxin (from CDC) - Clostridium tetani
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- Disease: tetanus
- Predisposing factor: trauma, usually stepping on nail
- Virulence: neurotoxin that blocks inhibition -> spastic paralysis -> lockjaw or "trismus" -> respiratory failure
- Treatment: antitoxin, vaccine, respiratory support, pen G or metronzidazole - D cycloserine
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- A D-Ala analogue=
- inhibits L-Ala racemase D-Ala and also D-Ala synthetase D-Ala-D-Ala - Vancomycin
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- binds D-Ala-D-Ala precursor blocking polymerization
- Also injures cytoplasmic membrane - Bacitracin
- - blocks regeneration of C55-isoprenol phosphate carrier.
- β-lactams (penicillins, cephalosporins)
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- block transpeptidation in crosslinking side chains
- Sonly formed by growing cells, so only act on growing cells - may be sufficient to "kill" some organisms - Aminoglycosides
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- streptomycin, kanamycin, gentamicin, tobramycin
- bind to 30S subunit -> misreading of code, release of ribosome from mRNA
- irreversible, cidal - Tetracyclines
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- act on 30S ribosome, inhibit aa-t-RNA binding to A site
- static, reversible - Macrolides
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- erythromycin, clindamycin clarithromycin, azithromycin
- act on 50S ribosome, block transfer and translocation
- static, reversible - Oxazolidinones
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- Linezolide - for resistant enterococcal and staph
- only against gram positives
- binds to 23S RNA on 50S, so no 70S
- static for staphy and enterococci,
- cidal for strep - Sulfonamides
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- antibacterials - dye derivs, not microbial products
- Inhibition (PABA) into FA b/c they are structural analogues of PABA - Trimethoprim
- inhibits DHT to THF
- Rifamycins
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- aromatic ring w/ long aliphatic bridge
- Rifampin binds to β subunit of RNA poly, no transcription
- high rates of mutation of target site is a problem - Quinolones
- - interfere with gyrase α, reformation of phosphodiester bond (rejoining DNA after ds cleavage by gyrase)
- Novobiocin
- - blocks binding of ATP to gyrase/DNA complex, interfering with gyrase β - decreased DNA supercoiling
- Peptostreptococcus
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- Gram positive cocci, anaerobe
- microflora in oropharynx and intestinal tract - Actinomyces
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- Gram positive non-spore- forming rods - anaerobes
- oropharynx - some microaerophilic
- resistant to metronidazole - Lactobacillus
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- Gram positive non-spore- forming rods - anaerobes
- female genital tract
- vancomycin resistant - Propionibacterium
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- Gram positive non-spore- forming rods - anaerobes
- microflora of skin
- common contaminant of CSF and blood cultures - bacteriods
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- Gram negative rods, anaerobes
- oropharynx and GI
- in female genital tract - the most common isolated in human infections - most produce beta-lactamse
- treated with a beta-lactam /beta lactamase inhibitor such as the combination of ampicillin and sulbactam or metronidazole. - Porphyromonas
- - Gram negative rods - anaerobes
- Prevotella
- - Gram negative rods - anaerobes
- Fusobacterium
- - Gram negative rods - anaerobes
- Brain abscess
- Prevotella, Porphyromonas, and Peptostreptococcus
- Device related meningitis
- Propionibacterium
- Deep fascial space infections
- Bacteroides, Prevotella, Porphyromonas, Peptostreptococcus, and Fusobacterium
- Lung abscess
- Bacteroides, Prevotella, Porphyromonas, Fusobacterium, and Peptostreptococcus
- Peritonitis
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Bacteroides fragilis
Escherichia coli
Peptostreptococcus
Prevotella - Female genital tract infections
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Peptostreptococcus, Prevotella, and Porphyromonas
B. fragilis if abscess - Foot infections
- Bacteroides and Peptostreptococcus