Gram-Positive Bugs Flashcards
Gram+, Catalase+, Coagulase+ cocci clusters
Staphylococcus aureus
- protein A binds Fc portion of IgG
- coagulase forms fibrin coat around organisms
- hemolysins and leukocidins destroy RBCs and WBCs
Gram+, Catalase+, Coagulase-, Novobiocin sensitive cocci clusters
Staphylococcus epidermidis
- Polysaccharide capsule allows adherence to inserted medical device
- Think S. epidermidis endocardtiis within 60 days of heart valve replacement. After 60 days, think Viridans
“NO SRESs”. Novobiocin - Saprophyticus Resistant, Epidermidis Sensitive
Gram+, Catalse+, Coagulase-, Novobiocin resistant cocci clusters
Staphylococcus saprophyticus
- 2nd most common cause of cystitis among sexually active young women (after E. coli); treat with TMP-SMX
“NO SRESs”. Novobiocin - Saprophyticus Resistant, Epidermidis Sensitive
Gram+, Catalase-, alpha-hemolytic, Optochin sensitive, Bile soluble (lysed by bile) Lancet-shaped diplococci
Streptococcus pneumoniae
- Capsule impairs phagocytosis (Quellung rxn +)
- IgA proteases
- Causes sepsis in patients with sickle cell or s/p splenectomy
- PPx with Pneumovax capsular polysaccharide vaccine
”OVRPS”. Optochin - Viridans is Resistant; Pneumoniae is Sensitive
Gram+, Catalase-, alpha-hemolytic, Optochin resistant, Bile insoluble (not lysed by bile) cocci chains
Streptocococus mutans/intermedius (Viridans Streptococcus)
- Capsule impaires phagocytosis (Quellung reaction)
- Viridans streptococci (as well as Enterococci) colonize previously-damaged heart valves
“OVRPS”. Optochin - Viridans is Resistant; Pneumoniae is Sensitive
Gram+, Catalase-, beta-hemolytic, Bacitracin-sensitive cocci chains
Streptococcus pyogenes (GAS)
- Adheres to pharyngeal epithelium via pili
- Streptokinase - converts plasminogen to plasmin
- M protein - resists phagocytosis
- Hyaluronidase - breaks down connective tissue
“B-BRAS”. Bacitracin - group B strep are Resistant, group A strep are Sensitive
Gram+, Catalse-, beta-hemolytic, Bacitracin-resistant cocci chains
Streptococcus agalactiae (GBS)
“B-BRAS”. Bacitracin - group B strep are Resistant, group A strep are Sensitive
Gram+, Catalase-, gamma-hemolytic, Growth in bile and 6.5% NaCl, cocci chains
Enterococcus faecalis (Group D streptococci)
- Capsule prevents degregation in bile
- Overgrows locally when normal flora is suppressed by cepahlosporins, leading to UTI and bilitary tract infections
- May colonize previously damaged heart valves s/p Gi/GU procedures
- Vancomycin-resistant enterococci (VRE) are important causes of nosocomial infections
Gram+, Catalase-, gamma-hemolytic, Growth in bile but NOT in 6.5% NaCl, cocci chains
Streptococcus bovis (Non-enterococci Group D streptococci)
- Capsule prevents bile salt degredation
- May cause subacute bacterial endocarditis in patients with colon cancer or IBD
Gram+, spore-forming, aerobic, motile bacilli
Bacillus cereus
- Heat-stable enterotoxin (cerulide, similar to Staph enterotoxin) causes emesis
- Heat-labile enterotoxin (like E. Coli LT) increases cAMP and causes diarrhea
Gram+, spore-forming, aerobic, non-motile bacilli
Bacillus anthracis
- Only bacterium with a polypeptide capsule (contains D-glutamate) instead of polysaccharide capsule
- Protective antigen (PA) binds cell membrane and mediates endocytic entry of EF or LF
- Edema factor (EF) increases cAMP and inhibits PMNs
- Lethal factor (LF) causes cell death
Gram+, spore-forming, obligate anaerobe, motile bacilli
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Clostriudium tetani
- Tetanospasmin toxin
- Tx: antitoxin, DTaP booster, pencillin/metronidazole, diazepam (GABA agonist)
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Clostridium botulinum
- Botulinum toxin (symmetric descending paralysis, floppy baby syndrome after honey ingestion)
- Tx: antitoxin, respiratory support
-
Clostridium difficile
- toxin A (watery diarrhea), toxin B (cytotoxin to epithelial cells, forms pseudomembrane)
Gram+, spore-forming, obligate anaerobe, non-motile bacilli
Clostridium perfringens
- Collagenase, hyaluronidase - degredative enzymes that cause slow, painless infection and crepitus
- Alpha toxins (lecithinase) - muscle cell necrosis
- Heat-labile enterotoxin (food-poisoning)
Gram+, non-spore-forming, motile bacillus
Listeria monocytogenes
- Heat-resistant organism survives in poorly pasteurized milk, penetrates GI mucosa, and invades phagocytes
- Also may be acquired via transplacental transmission or vaginal transmission during delivery
- “Rocket tails” via actin polymerization allow it to avoid Ab
- Tumbling motility
- Catalase-positive
- Only gram-positive bug that produces LPS
Gram+, non-spore-forming, non-motile bacillus
Cornyebacterium diphteriae
- Pseudomembranes in nasopharynx that may block airway
- AB toxin (phage-mediated) ADP ribsoylates EF-2, leading to arrhythmias, mycocarditis, and cranial and peripheral nerve palsy
- Black colonies with Chinese-letter appearance on potassium tellurite culture
- Tx: antitoxin, pencillin/erythromycin, DTaP booster
