Clinical Bacteriology Flashcards
Gram +, bacilli, aerobic
Listeria, Bacillus, Corynebacterium
Gram +, bacilli, anaerobic
Clostridium, Propionibacterium
Gram +, cocci, anaerobic/facultative, catalase -, alpha hemolysis, optochin/bile resistant
Viridans streptococci (no capsule): S mutans, S mitis
Gram +, cocci, anaerobic/facultative, catalase -, alpha hemolysis, optochin/bile sensitive
S. pneumoniae (encapsulated)
Gram +, cocci, anaerobic/facultative, catalase -, beta hemolysis, bacitracin resistant
Group B strep: S agalactiae
Gram +, cocci, anaerobic/facultative, catalase -, beta hemolysis, bacitracin sensitive
Group A strep: S pyogenes
Gram +, cocci, anaerobic/facultative, catalase -, gamma hemolysis, no growth in 6.5% NaCl
Nonenterococcus, S bovis
Gram +, cocci, anaerobic/facultative, catalase -, gamma hemolysis, growth in 6.5% NaCl
Group D (enterococcus): E faecium, E faecalis Note: can also be alpha hemolytic
Gram +, cocci, anaerobic/facultative, catalase +, coagulase -, novobiocin resistant
S saprophyticus
Gram +, cocci, anaerobic/facultative, catalase +, coagulase -, novobiocin sensitive
S epidermidis
Gram +, cocci, anaerobic/facultative, catalase +, coagulase +
S aureus
Alpha-hemolysis
Gram + cocci
Partial reduction of hemoglobin causes greenish or brownish color without clearing around growth on blood agar
Beta-hemolysis
Gram + cocci
Complete lysis of RBCs -> clear area surrounding colony on blood agar
Staphylococcus aureus - virulence factor
Protein A: binds Fc-IgG, inhibiting complement activation and phagocytosis
Staphylococcus aureus - colonization
Nares, axilla, and groin
Staphylococcus aureus - infections
Inflammatory disease, toxin-mediated disease, MRSA
Staphylococcus aureus - inflammatory disease
Skin infections, organ abscesses, pneumonia (only after influenza virus infection), endocarditis, septic arthritis, and osteomyelitis
Staphylococcus aureus - organ abscess formation
“Bad staph” make coagulase and toxins
Forms fibrin clot around self -> abscess
Staphylococcus aureus - toxin-mediated disease
Toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid onset food poisoning (enterotoxins)
Staphylococcus aureus - MRSA infection
Methicillin-resistant Staphylococcus aureus
Important cause of serious nosocomial and community-acquired infections
Resistant to methicillin and nafcillin because of altered penicillin-binding protein
Staphylococcal toxic shock syndrome - presentation
Fever, vomiting, rash, desquamation, shock, end-organ failure
Staphylococcal toxic shock syndrome - labs
Increased AST, increased ALT, increased bilirubin
Staphylococcal toxic shock syndrome - common association
Prolonged use of vaginal tampons or nasal packing
TSST-1 - mechanism
Superantigen that binds to MHCII and T-cell receptor, resulting in polyclonal T-cell activation
S aureus food poisoning - cause
Ingestion of preformed toxin -> short incubation period
Enterotoxin is heat stable -> not destroyed by cooking
S aureus food poisoning - presentation
Quick onset (2-6 hours), non bloody diarrhea and emesis
Staphylococcus epidermidis - colonization
Normal flora of skin
Contaminates blood cultures
Staphylococcus epidermidis - infection sites
Prosthetic devices (eg, hip implant, heart valve) and IV catheters by producing adherent biofilms
Staphylococcus saprophyticus - colonization
Normal flora of female genital tract and perineum
Staphylococcus saprophyticus - infection
Second most common cause of uncomplicated UTI in young women (E coli most common)
Streptococcus pneumoniae - shape
Lancet-shaped diplococci
Streptococcus pneumoniae - virulence
Encapsulated (no virulence without the capsule)
IgA protease
Streptococcus pneumoniae - common diseases
Most common cause of: Meningitis Otitis media (in children) Bacterial pneumonia Sinusitis
Pneumococcus - associations
“Rusty” sputum
Sepsis in patients with sickle cell disease and asplenic patients
Viridans group streptococci - colonization
Normal flora of the oropharynx
Viridans group streptococci - infections
Dental caries (S mutans and S mitis) Subacute bacterial endocarditis at damaged heart valves (S sanguinis)
S sanguinis - endocarditis mechanism
Makes dextran, which bind to fibrin-platelet aggregated on damaged heart valves
Streptococcus pyogenes - pyogenic infections
Pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas
Streptococcus pyogenes - toxigenic infections
Scarlet fever, toxic shock-like syndrome, necrotizing fasciitis
Streptococcus pyogenes - immunologic infections
Rheumatic fever, post-streptococcal glomerulonephritis
Streptococcus pyogenes - virulence
Hyaluronic acid capsule inhibits phagocytosis
Streptococcus pyogenes - autoimmunity
Antibodies agains M protein enhance host defenses against S pyogenes but can give rise to rheumatic fever
Streptococcus pyogenes - recent infection test
ASO titer or anti-DNase B antibodies indicate recent S pyogenes infection
Streptococcus pyogenes - complications
Pharyngitis: rheumatic fever and glomerulonephritis
Impetigo: glomerulonephritis
Scarlet fever - presentation
Blanching, sandpaper-like body rash, strawberry tongue and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin +)
