Microbiology- Clinical Bacteriology (Gram +) Flashcards
(45 cards)
Gram-positive lab algorithm
pag. 134
Gram-positive cocci antibiotic tests:
Staphylococci
NO StRESs.
NOvobiocin—Saprophyticus is Resistant; Epidermidis is Sensitive.
Gram-positive cocci antibiotic tests:
Streptococci
OVRPS (overpass).
Optochin—Viridans is Resistant; Pneumoniae is Sensitive.
B-BRAS.
Bacitracin—group B strep are Resistant; group A strep are Sensitive.
Gram-positive cocci antibiotic tests:
α-hemolytic bacteria
Gram ⊕ cocci. Partial reduction of hemoglobin causes greenish or brownish color without clearing around growth on blood agar.
Streptococcus pneumoniae (catalase ⊝ and optochin sensitive)
Viridans streptococci (catalase ⊝ and optochin resistant)
Gram-positive cocci antibiotic tests:
β-hemolytic bacteria
Gram ⊕ cocci. Complete lysis of RBCs clear area surrounding colony on blood agar.
Staphylococcus aureus (catalase and coagulase ⊕)
Streptococcus pyogenes—group A strep (catalase ⊝ and bacitracin sensitive)
Streptococcus agalactiae—group B strep (catalase ⊝ and bacitracin resistant)
Staphylococcal toxic shock syndrome (TSS)
fever, vomiting, rash, desquamation, shock, end-organ failure. TSS results in AST, ALT, bilirubin. Associated with prolonged use of vaginal tampons or nasal packing.
S aureus food poisoning
due to ingestion of preformed toxin short incubation period (2–6 hr) followed by nonbloody diarrhea and emesis. Enterotoxin is heat stable not destroyed by cooking.
MRSA (methicillin-resistant S aureus)
Important cause of serious nosocomial and community-acquired infections; resistant to methicillin and nafcillin because of altered penicillin-binding protein.
S. aeureus Inflammatory disease
skin infections, organ abscesses, pneumonia (often after
influenza virus infection), endocarditis, septic arthritis, and osteomyelitis.
S. aeureus Toxin-mediated disease
toxic shock syndrome (TSST-1), scalded skin syndrome
exfoliative toxin), rapid-onset food poisoning (enterotoxins
Staphylococcus epidermidis Disease
Normal flora of skin; contaminates blood cultures.
Infects prosthetic devices (eg, hip implant, heart valve) and IV catheters by producing adherent biofilms.
Staphylococcus saprophyticus Disease
Normal flora of female genital tract and perineum.
Second most common cause of uncomplicated UTI in young women (most common is E coli).
Streptococcus pneumoniae Disease
Most common cause of: Meningitis Otitis media (in children) Pneumonia Sinusitis
Viridans group streptococci Disease
Streptococcus mutans and S mitis cause dental caries.
S sanguinis makes dextrans that bind to fibrinplatelet
aggregates on damaged heart valves, causing subacute bacterial endocarditis.
*Normal flora of the oropharynx.
Streptococcus pyogenes (group A streptococci) Disease
Cause:
Pyogenic—pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas.
Toxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis.
Immunologic—rheumatic fever, glomerulonephritis.
Scarlet fever
blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕).
Streptococcus pyogenes (group A streptococci) Tests
Bacitracin sensitive, β-hemolytic, pyrrolidonyl arylamidase (PYR) ⊕.
Hyaluronic acid capsule and M protein inhibit phagocytosis. Antibodies to M protein can give rise to rheumatic fever.
ASO titer or anti-DNas B antibodies indicate recent S pyogenes infection.
Streptococcus agalactiae (group B streptococci) Disease
colonizes vagina; causes pneumonia, meningitis, and sepsis, mainly in babies.
Hippurate test ⊕. PYR ⊝.
Streptococcus agalactiae (group B streptococci) screening
Screen pregnant women at 35–37 weeks of gestation with rectal and vaginal swabs.
Patients with ⊕ culture receive intrapartum
penicillin prophylaxis.
Streptococcus bovis Disease
Bovis in the blood = cancer in the colon.
colonizes the gut. S gallolyticus (S bovis biotype 1) can cause bacteremia and subacute endocarditis and is associated with colon cancer.
Enterococci (E faecalis and E faecium) Disease
Catalase ⊝, PYR ⊕, variable hemolysis.
Normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures).
VRE (vancomycin-resistant enterococci) are an important cause of nosocomial infection.
Bacillus anthracis Characteristics
Gram ⊕, spore-forming rod that produces anthrax toxin.
The only bacterium with a polypeptide capsule (contains d-glutamate).
Colonies show a halo of projections, sometimes referred to as “medusa head” appearance.
Cutaneous anthrax
Painless papule surrounded by vesicles, ulcer with black eschar (painless, necrotic), uncommonly progresses to bacteremia and death.
Pulmonary anthrax
Inhalation of spores, flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock. Also known as woolsorter’s disease. CXR may show widened mediastinum.
