Gram Positive Bacteria Flashcards
Staphylococcus aureus
gram-positive cocci in clusters
catalase positive, coagulase postive
Protein A (binds Fc-IgG inhibiting complement fixation and phagocytosis)
Inflammatory disease:
skin infections, organ abscesses, pneumonia
Toxin-mediated:
toxic shock syndrome (TSST-1) - superantigen that binds MHC II and T-cell receptors –> polyclonal T-cell activation
– fever, vomiting, desquamation, shock, end-organ failure
scalded skin syndrome (exofoliative toxin)
rapid-onset food poisoning (enterotoxins) - custard, mayo, salted meat
MRSA infection:
important cause of serious nosocomial and community-acquired infection; resistant to beta-lactams b/c of altered penicillin-binding protein
Acute bacterial endocarditis, osteomyelitis
Staphylococcus epidermidis
gram-positive, cocci
catalase positive, coagulase negative, novobiocin sensitive
infects prosthetic devices and IV catheters by producing adherent biofilms
normal skin flora; contaminates blood cultures
Biofilms - synthesis of extracellular polysaccharide matrix that encase the bacteria
treatment: vancomycin, rifampin
Streptococcus pneumoniae
lancet-shaped, gram-positive diplococci; encapsulated, IgA protease;
catalase negative, alpha hemolytic (partial green); optochin sensitive
Meningitis
Otitis media
Pneumonia
Sinusitis
“rusty” sputum, sepsis in sickle cell anemia and splenectomy
no virulence without capsule
Viridans group strep
gram-positive cocci, no capsule
catalase negative, alpha hemolytic, optochin resistant
normal oropharynx flora
S. mutans - dental caries
S. sanguis - subacute bacterial endocarditis at (bind to damaged valve by making glycocalyx)
antibiotic prophylaxis used prior to dental work for patient with heart problems
able to make dextrans from sucrose –> helps in colonization of host surfaces
Strep pyogenes (group A)
gram-positive cocci
catalase negative, beta hemolytic (complete clear), bacitracin sensitive
Pyogenic:
pharyngitis - gray-white tonsillar exudate, PYR positive
cellulitis
impetigo (more commonly preceded glomerulonephritis than pharyngitis)
Toxigenic:
scarlet fever - scarlet rash sparing face, strawberry (scarlet) tongue, scarlet throat
toxic shock-like syndrome, nectrotizing fasciitis
Immunologic - RF, acute glomerulonephritis
antibodies to M protein enhance host defenses against but can give rise to rheumatic fever
ASO titer detects infection
Strep agalactiae
group B strep
gram-positive cocci
catalase negative, beta hemolytic, bacitracin resistant
colonizes vagina
pneumonia, meninfitis, and sepsis in babies
produces CAMP factor, which enlarges the area of hemolysis formed by S. aureus
Hippurate test positive
Screen pregnant women at 35-37 weeks – positive –> intrapartum penicillin prophylaxis
Enterocooci
group D strep
gram-positive cocci
catalase negative, non hemolysis, growth in bile and 6.5% NaCl
normal colonic flora that are penicillin G resistant
UTI, biliary tract infection, subacute endocarditis
lancefield grouping is based on differences in C carbohydrate on the bacterial cell wall
VRE - nosocomial infection
Strep bovis
group D strep
colonizes the gut
bacteremia, subacute endocaritis in colon cancer patients
Cornebacterium diphtheriae
gram-positive rod
metachromic (blue and red) granules and Elek’s test for toxin
black colonies on cystine-tellurite agar
diphteria via exotoxin encoded by beta-phage
exotoxin inhibits protein synthesis via ADP ribosylation of EF-2
pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy, myocarditis, and arrhythmias
toxoid vaccine prevents it
C. tetani
gram-positive, spore-forming, obligate anaerobic bacilli
found in soil
produces tetanospasmin, exotoxin causing tenanus
block GABA and glycine release
spastic paralysis, trismus (lockjaw), risus sardonicus
C. botulinum
gram-positive, spore-forming, obligate anaerobic bacilli
produces a preformed, heat-labile toxin that inhibits Ach release
adults - ingestion of preformed toxin
babies - ingestion of spores (honey)
C. perfringens
gram-positive, spore-forming, obligate anaerobic bacilli
found in soil
produces alpha toxin (lecithinase - phospholipase)
causes myonecrosis (gas gangrene) and hemolysis
C. difficile
gram-positive, spore-forming, obligate anaerobic bacilli
produces 2 toxins:
Toxin A - enterotoxin - binds to brush border of gut
Toxin B - cytotoxin - destroys the cytoskeletal structure of enterocytes –> pseudomembanous colitis (white/yellow membrane-like plaques on colonoscopy)
often secondary to antibiotic use (clindamycin or ampicillin)
diagnosed by PCR detection of toxins in stool
treatment: metronidazole or oral vancomycin
Bacillus anthracis
gram-positive, spore-forming rod
found in soil
produces anthrax toxin
polypeptide capsule containing D-glutamate
Cutaneous anthrax:
contact –> black eschar (painless ulcer); can progress to bacteremia and death
black skin lesions - black eschar surrounded by edematous ring (lethal factor and edema factor)
Pulmonary anthrax:
inhalation of spores –> flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock
woolsorter’s disease - inhalation of spores from contaminated wool
Bacillus cereus
gram-positive, spore-forming rod
cause food poisoning
spores survive cooking rice, keeping rice warm results in germination of spores and enterotoxin formation
emetic type - nausea and vomiting within 1-5 hours caused by cereulide, preformed toxin
diarrheal type - watery, nonbloody diarrhea and GI pain in 8-18 hours
