Gram-Positive Bugs Flashcards

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1
Q

Gram+, Catalase+, Coagulase+ cocci clusters

A

Staphylococcus aureus

  • protein A binds Fc portion of IgG
  • coagulase forms fibrin coat around organisms
  • hemolysins and leukocidins destroy RBCs and WBCs
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2
Q

Gram+, Catalase+, Coagulase-, Novobiocin sensitive cocci clusters

A

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

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3
Q

Gram+, Catalse+, Coagulase-, Novobiocin resistant cocci clusters

A

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

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4
Q

Gram+, Catalase-, alpha-hemolytic, Optochin sensitive, Bile soluble (lysed by bile) Lancet-shaped diplococci

A

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

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5
Q

Gram+, Catalase-, alpha-hemolytic, Optochin resistant, Bile insoluble (not lysed by bile) cocci chains

A

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

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6
Q

Gram+, Catalase-, beta-hemolytic, Bacitracin-sensitive cocci chains

A

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

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7
Q

Gram+, Catalse-, beta-hemolytic, Bacitracin-resistant cocci chains

A

Streptococcus agalactiae (GBS)

“B-BRAS”. Bacitracin - group B strep are Resistant, group A strep are Sensitive

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8
Q

Gram+, Catalase-, gamma-hemolytic, Growth in bile and 6.5% NaCl, cocci chains

A

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
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9
Q

Gram+, Catalase-, gamma-hemolytic, Growth in bile but NOT in 6.5% NaCl, cocci chains

A

Streptococcus bovis (Non-enterococci Group D streptococci)

  • Capsule prevents bile salt degredation
  • May cause subacute bacterial endocarditis in patients with colon cancer or IBD
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10
Q

Gram+, spore-forming, aerobic, motile bacilli

A

Bacillus cereus

  • Heat-stable enterotoxin (cerulide, similar to Staph enterotoxin) causes emesis
  • Heat-labile enterotoxin (like E. Coli LT) increases cAMP and causes diarrhea
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11
Q

Gram+, spore-forming, aerobic, non-motile bacilli

A

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
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12
Q

Gram+, spore-forming, obligate anaerobe, motile bacilli

A
  • Clostriudium tetani
    • Tetanospasmin toxin
    • Tx: antitoxin, DTaP booster, pencillin/metronidazole, diazepam (GABA agonist)
  • 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)
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13
Q

Gram+, spore-forming, obligate anaerobe, non-motile bacilli

A

Clostridium perfringens

  • Collagenase, hyaluronidase - degredative enzymes that cause slow, painless infection and crepitus
  • Alpha toxins (lecithinase) - muscle cell necrosis
  • Heat-labile enterotoxin (food-poisoning)
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14
Q

Gram+, non-spore-forming, motile bacillus

A

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
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15
Q

Gram+, non-spore-forming, non-motile bacillus

A

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
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16
Q

Gram+, non-acid-fast, obligate anaerobe beaded filaments

A

Actinomyces israelii

  • Normal flora of oral cavity, GI tract, female GU tract that can form pus-filled abscesses and draining sinus tracts with disruption of the mucosal border
  • Yellow sulfur granules (filamentous bacteria lined by eosinophilic proteinaceous coating) surrounded by PMNs
  • Tx: penicillin
17
Q

Gram+, acid-fast, obligate aerobe beaded filaments

A

Nocardia asteroides, Nocardia brasiliensis

  • Frequently found in soil, inhaled, and phagocytosed
  • Caseous granulomas form around infectious particles, leading to pneumonia and abscesses in kidney and brain
  • Most common in immunocompromised patients
  • Tx: TMP-SMX