Microbiology: Gram Positive Bacteria

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jknell
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Microbiology: Gram Positive Bacteria
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2013-04-05 12:11:37
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  1. Gram Positive Algorithm
  2. Identification of G+ Cocci
    Catalase+: Staphylococcus

    • "On the office's staph retreat there was NO StRESs"
    • NOvobiocin: Saprophyticus is Resistant; Epidermidis is Sensitive

    Catalase-: Streptococci

    • "OVRPS" (overpass)
    • Optocin: Viridans is Resistant; Pneumoniae is Sensitive

    • "B-BRAS"
    • Bacitracin: group B strep are Resistant; group A strep are Sensitive
  3. Hemolysis
    • alpha: partial
    • beta: complete
    • gamma: none
  4. Alpha hemolytic Bacteria
    -green ring on agar

    • Strep pneumo (optochin sensitive)
    • Viridans Strep (optochin resistant)
  5. Beta hemolytic Bacteria
    -clear ring on blood agar

    • Strep pyogenes (Group A strep)
    • Strep agalactiae (Group B strep)
    • Staph aureus
    • Listeria monocytogenes
  6. Staphylococcus aureus


    • G+ Cocci in clusters
    • -catalase+
    • -coagulase+
    • -Protein A (binds IgG)
    • -TSST1 superantigen (TSS)

    Forms fibrin clot around self --> abscess

    • Presentation:
    • 1. Inflammatory Disease
    •      -skin infection
    •      -organ abscesses
    •      -pneumonia
    • 2. Toxin-mediated Disease
    •       -TSS (TSST1)
    •      -Scalded skin syndrome (exfoliative toxin)
    •      -rapid onset food poisoning (ingestion of preformed entertoxins)
    • 3. MRSA (methicillin resistant)
    • 4. Acute bacterial Endocarditis
    • 5. Osteomyelitis
  7. Staphylococcus epidermidis
    • G+ Cocci in clusters
    • -catalase+
    • -coagulase-
    • -Novobiocin Sensitive

    • -infects prosthetic devices and IV catheters
    • -produces adherent biofilms
    • -component of normal skin flora
    • -contaminates blood culture
  8. Streptoccucs pneumoniae
    • G+ diplococci (lancet shaped)
    • -catalase-
    • -alpha hemolytic
    • -optochin sensitive
    • -encapsulated (not virulent w/o capsule)
    • -IgA protease

    • Most Common Cause of:
    •      -Meningitis
    •      -Otitis media (children)
    •      -Pneumonia
    •      -Sinusitis
    • "S. pneumo MOPS are Most OPtochin Sensitive"

    • -Associated with "rusty" sputum
    • -Sepsis in SCA and asplenia
  9. Viridans Streptococci
    • G+ Cocci in chains
    • -catalase-
    • -alpha hemolytic
    • -optochin resistant

    -normal flora of oropharynx

    • Streptococcus mutans: dental caries
    • Streptococcus sanguis: subacute bacterial endocarditis at damaged valves

    -Glycocalyx allows S. sanguis to stick to valves

    "Viridans group strep live in the mouth because they are not afraid of-the-chin (optochin)"
  10. Streptococcus pyogenes (Group A Strep)
    • G+ Cocci in chains
    • -Catalase-
    • -beta hemolytic
    • -bacitracin sensitive

    • Causes:
    • 1. Pyogenic
    •      -pharyngitis
    •      -cellulitis
    •      -impetigo
    • 2. Toxigenic
    •      -Scarlet Fever
    •      -Toxic Shock-Like Syndrome
    •      -Necrotizing Fascitis
    • 3. Immunologic:
    •      -Rheumatic Fever
    •      -Acute Glomerulonephritis

    Antibodies to M protein: host defense, also cause RF

    ASO titre: recent S. pyogenes infection

    Glomerulonephritis more commonly preceded by impetigo than pharyngitis

    "Pharyngitis can result in rheumatic phever and glomerulonephritis"

    Scarlet Fever: rash sparing face, strawberry tongue, scarlet throat

    • JNES Criteria for Rheumatic Fever
    • -Joints: Polyarthritis

    • -: endocarditis
    • -Nodules (subcutaneous)
    • -Erythema marginatum (pink ring on trunk/inner surface of limbs)
    • -Sydenham's chorea (primarily face, feet and hands)
  11. Streptococcus agalactiae (Group B Strep)
    • G+ Cocci in chains
    • -catalase-
    • -Beta hemolytic
    • -Bacitracin resistant

    Colonize vagina

    • Causes:
    • 1. Pneumonia
    • 2. Meningitis
    • 3. Sepsis

    "Group B for Babies!"

    CAMP factor: enlarges area of hemolysis formed by S. aureus

    Hippurate test positive

    • Screen pregnant women at 35-37 weeks
    • Intrapartum penicillin prophylaxis
  12. Enterococci (Group D streptococci)
    • G+ cocci in chains
    • -catalase-
    • -variable hemolysis (gamma)
    • -grows in 6.5% NaCl and bile (hardy)

    • E. faecalis
    • E. faecium

    • Normal colonic flora
    • PCN G resistant

    • Cause:
    • 1. UTI
    • 2. Biliary Tract Infections
    • 3. Subacute Endocarditis

    Lancefield grouping (includes enterocci and non-enterococci)

    VRE important cause of nosocomial infection
  13. Streptococcus bovis (Group D streptococci)
    • G+ cocci in chains
    • -Catalase-
    • -gamma hemolysis
    • -sensitive to 6.5% NaCl
    • -grows in bile

    Colonizes the gut

    • Causes:
    • 1. Bacteremia and acute endocarditis in colon cancer patients

    "Bovis in the blood = cancer in the colon"
  14. Corynebacterium diphtheriae
    • G+ bacilli
    • -Coryne = "club shaped"
    • -metachromatic granules (blue and red)
    • -Elek's test for toxins
    • -Black colonies on cystine-tellurite agar

    • Diphtheria
    • -pseudomembranous pharyngitis (grayish-white membrane)
    • -lymphadenopathy
    • -myocarditis
    • -arrhythmias
    • exotoxin inhibits protein synthesis via ADP-ribosylation of EF2

    • "ABCDEFG"
    • -ADP-Ribosylation
    • -Beta-prophage
    • -Corynebacterium
    • -Diphtheria
    • -Elongation Factor 2
    • -Granules

    Prevention: toxoid vaccine
  15. Clostridia
    • G+ bacillus
    • -spore forming
    • -obilgate anaerobe

    • C tetani
    • C botulinum
    • C perfringens
    • C difficile
  16. Clostridium tetani
    Tetanospasmin: exotoxin that causes tetanus, protease cleaves releasing protein for NTs

    Blocks GABA and glycine release from Renshaw cells in the spinal cord

    • Presentation:
    • -spastic paralysis
    • -trismus (lockjaw)
    • -risus sardonicus
  17. Clostridium botulinum
    • Botulinum toxin:
    • -heat labile
    • -inhibits ACh release at NMJ

    • Adults: ingestion of preformed toxin
    • Children: ingestion of spores in honey (floppy baby syndrome)
  18. Clostridium perfringens
    • alpha toxin:
    • -lecithinase (phospholipase)
    • -causes myonecrosis (gas gangrene) and hemolysis

    "Perfringens perforates a gangrenous leg"
  19. Clostridium difficile
    • Toxin A:
    • -enterotoxin
    • -binds brush border of the gut

    • Toxin B:
    • -cytotoxin
    • -destroys cytoskeleton of enterocytes
    • -causes pseudomembranous colitis

    Often secondary to antibiotic use (Clindamycin or ampicillin)

    Diagnosis: detection of toxins in stool

    Treatment: metronidazole, oral vancomycin
  20. Bacillus anthracis
    • G+ rod
    • -spore forming
    • -only bug with polypetide capsule (D-glutamate)
    • -anthrax toxin

    • Cutaneous anthrax:
    • -Transmission: contact
    • -black eschar (necrosis surrounded by edema, caused by lethal factor and edema factor, painless ulcer)
    • -can progress to bacteremia and death

    • Pulmonary anthrax:
    • -Transmission: inhalation of spores (contaminated wool)
    • -flu-like sx
    • -rapidly progresses to fever
    • -pulmonary hemorrhage
    • -mediastinitis
    • -shock
    • -"woolsorter's disease'
  21. Bacillus cereus
    G+ rod

    • "reheated rice syndrome"
    • -spores survive in cooking rice
    • -keeping rice warm --> germination and enterotoxin formation

    • Emetic type
    • -rice and pasta
    • -N/V within 1-5 hrs
    • -cereulide: preformed toxin

    • Diarrheal type
    • -watery non-bloody diarrhea
    • -GI pain
    • -8-18hrs
  22. Listeria monocytogenes
    • G+ rod
    • -facultative intracellular

    -unpasteurized milk/cheese, deli meats, vaginal transmission during birth

    • -"actin rockets"
    • -tumbling motility

    • Cause:
    • -In pregnant women (amnionitis, septicemia, spontaneous abortion)
    • -neonatal meningitis
    • -meningitis in immunocompromised
    • -mild gastroenteritis in healthy

    • Treatment:
    • -gastroenteritis = self limited
    • -Infants: ampicillin
    • -Immunocompromised/elderly: empiric tx of meningitis
  23. Actinomyces israeli
    • G+
    • -anaerobe
    • -branching filaments (resemble fungi)

    NOT acid fast

    Normal oral flora

    • Causes:
    • -facial/oral abscesses
    • -drain through sinus tracts
    • -yellow sulfur granules

    Tx: penicillin
  24. Nocardia
    • G+
    • -aerobe
    • -branching filaments

    acid fast

    Found in soil

    • Causes:
    • -pulmonary infections in immunocompromised
    • -cutaneous infections after trauma in immunocompetent

    Tx: sulfonamides
  25. Mycobacterium: Tuberculosis
    • 1. M tuberculosis
    • -often resistant to multiple drugs

    • 2. M kansaii
    • -pulmonary TB-like sx

    • 3. M avium-intracellulare
    • -disseminated non-TB disease in AIDS
    • -often resistant to multiple drugs
    • -prophylaxis with azithromycin


    • TB sx:
    • -fever
    • -night sweats
    • -weight loss
    • -hemoptysis

    • Cord factor
    • -in virulent strains
    • -inhibits MP maturation
    • -induces TNFa release

    • Sulfatides
    • -surface glycolipids
    • -inhibit phagolysosome
  26. Mycobacterium: Leprosy
    M. leprae

    • -infects skin and superficial nerves
    • -likes cool temperatures (glove and stocking loss of sensation)
    • -reservoir = armadillos

    • Lepromatous
    • -diffusely over skin
    • -communicable
    • -low cell-mediated immunity with humoral Th2 response
    • "lepromatous can be lethal"
    • Treatment:
    • -2-5y: dapsone, rifampine, clofazimine

    • Tuberculoid
    • -hypoesthetic hairless skin plaques
    • -high cell-mediated immunity with largely Th1 response
    • Treatment:
    • -multidrug therapy 6 mo: dapsone and rifampine

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