Gram + Cocci (Kaul) Flashcards
Main genera of gram + Cocci
- Streptococcus
- Staphylococcus
- Enterococcus
Staphylococcus (appearance, common residence, aerobicity, common infections, differential test)
- “Bunch of grapes” clusters
- Normal skin flora
- Facultative anaerobe
- Persistent on fomites
- Wound and nosocomial infections (since on skin normally)
- Catalase + (distinguish from streptococci, -)
Staphylococcus Aureus (features: differential test, appearance, location on humans, virulence factors)
- Coagulase + (distinguish from other staph)
- Golden colonies on agar
- Common on human nares
- Virulence Factors: Cytotoxins (hemolysins (lyse RBCs), PVL (leukocidins-lyse WBCs)), Superantigenic toxins (TSST-1, Exfoliatin, Enterotoxin), Invasins (staphylokinase, hyaluronidase, lipase- all used to penetrate tissue), Cell surface (Microcapsule (antiphagocytic), Protein A (anti-opsonization), Adhesin)
S. aureus: Superantigenic toxins
- TSST-1 (toxic shock syndrome toxin), enterotoxins, exfoliatin
- Non-specifically cross-link MHC–>TCR, activating up to 20% of T-cells, way too many cytokines,
Clinical manifestations of S. aureus infections (A4, B5, C3)
A. Skin and soft tissue infections (SSTIs)
1) Furuncles (small pus-filled local infections- look like pimple)
2) Carbuncle (larger skin abcess
3) Impetigo (spreading, crusting skin infection)
4) Cellulitis (deep skin infection)
B. Infections of other tissues
1) Osteomyelitis (bone infection)
2) Septic joint/arthritis (especially in kids)
3) Pneumonia
4) Acute Endocarditis (from IV drug abuse, gets in blood, grow on heart valve, cause embolism
5) Bacteremia/Septicemia
C. Toxinoses
1) Toxic Shock Syndrome (from TSST- fever, rash, multiorgan failure)
2) Gastroenteritis (“Food Poisoning”from enterotoxins- ACUTE onset GI, projectile vomiting)
3) Scalded Skin Syndrome (exfoliatin toxin causes red flush–>blisters–>bullous impetigo–>desquamination of epidermis
S. aureus drug treatment (resistance and what works(4))
- Resistant to penicillins, then MRSA and VRSA emerging
- Vancomycin, daptomycin, linezolid, ceftaroline
Coagulase - staph
- S. epidermis
- S. saprophyticus
S. epidermis (where resides, common infections, notable properties, resistance, treatment)
- normal skin flora
- infections with wounds
- less virulent than s. aureus
- makes biofilms
- resistant to penicillins, oxacillins
- nosocomial/opportunistic infections common
- Treat with vancomycin
S. saprophyticus (residence, infections, resistance, treatment)
- Normal vaginal flora
- Common infections: UTIs, cystitis in women
- Resistance to novobiocin
- Sensitive to penicillin G
Streptococcus (appearance, distinguishing test, growth requirements, classification factors (2))
- ovoid cocci in chains/pairs
- Catalase - (distinguish from staph)
- Fastidious, enriched media (distinguish from staph - grow on fomites)
- Aerotolerant anaerobes
- Classify based on cell wall antigen and hemolyis pattern
Types of Hemolysis (3)
Alpha- Damage RBCs, peroxide turns Hb brown
Beta- total RBC hemolysis, reveals yellow agar under blood
Gamma- none
Streptococcus Lancefield Groups
- serologic classification based on c-substance (cell wall antigen)
- A-U - A, B, D, none are common human pathogens
ß-hemolytic strep (division, lancefield group, species)
- Divide by bacitracin sensitivity or not
- Group A: bacitracin sensitive - S. pyogenes
- Group B: bacitracin resistant - S. agalactiae
Alpha-hemolytic streptococci (Distinguishing test, lancefield groups, species
- Optochin sensitivity
- Non-lancefield group strep
- Optochin sensitive: S. pneumoniae
- Optochin resistant: Viridans Group (s. mitis, other oral strep)
Gamma hemolytic strep (distinguishing test, lancefield group, species)
- Group D strep (S. bovis)
- Enterococci also fit here even though not strep
Group A strep (virulence factors (4), residence, infections, serious infection progression)
- S. pyogenes
- Virulence factors: M-protein (variable surface antigen allows reinfection), streptolysins S + O (lyse RBCs - “ASO titers”), streptococcal pryogenic exotoxins, streptokinase (invasin)
- Inhabit throat, nasopharynx
- mainly skin/throat infections, common in kids
- Infection can progress to rheumatic fever, acute glomerulonephritis
Clinical manifestation of Group A strep infection (3), progression if untreated (2)
- s. pyrogenes
1) streptococcal pharyngitis (strep throat). Associated with scarlet fever (toxin-mediated skin rash)
2) streptococcal skin infections (impetigo or erysypelas –>cellulitis/necrotizing fasciitis)
3) streptococcal toxic shock syndrome (superantigenic pyrogenic toxin)
If left untreated:
1) Rheumatic fever (antibodies vs. strep M-proteins cause myocarditis, chorea, fever 2-3 weeks AFTER pharyngitis)
2) Acute glomerulonephritis (type III hypersensitivity cause complex deposition in kidneys, block causing fluid retention)
Group B Strep
- S. agalactiae
- Normal vaginal flora
- cause of neonatal sepsis (infant infected on exit)
Viridans Group Strep
- non-lancefield (ABD), along with S. pneumoniae
- S. mitis, mutans, oralis, salivarus, sanguis, milleri
- oral cavity residents
- infection common from oral surgery facilitating entrance
- Clinical manifestations: dental caries, subacute endocarditis (blood-borne infection settles on heart valves- takes longer than acute-strep)
S. pneumoniae (appearance, virulence factors, residence, predisposed people, differentiating tests)
- non-lancefield group strep (along with viridans)
- pairs and short chains, “lancet shaped”
- also called pneumococci
- Virulence factors: polysaccharide capsule (antiphagocytic)
- Normal flora of nasopharynx
- predisposed: young/old/pregnant/immunocompromised/smoker/sickle cell/splenectomy
- Differentiate: green colonies (“viridans”), optochin sensitive, lysis by bile acid, Quelling reaction (swell due to capsule)
S. pneumoniae clinical manifestations (4), resistance (1) and drug treatment (2)
1) Lobar pneumoniae (whole lobe, unlike bronchitis)
2) Otitis media (middle ear infection via eustachean tube, common in kids)
3) Meningitis (common adult cause, stiff neck)
4) Bacteremia/septicemia
Resistance: penicillins
Treatment: 3rd gen. cephalosporins (cefotaximes, ceftriaxone)
S. pneumoniae vaccine
- Pneumovax (PPV)
- recommended for immunocompromised or 65+ people
- Prevnar (PCV-13)
- recommended for kids under 5, 65+
Group D strep (species, infection)
- S. bovis, enterococci
- gamma/alpha hemolytic
- S. bovis bacteremia associated with GI malignancy/colon cancer
Enterococci (species, lancefield, residence, infection, differentiating tests, resistance/treatment)
Group D strep antigens, E. faecium/faecalis
- normal GI flora
- nosocomial infection (can live on fomites)/multidrug resistance
- opportunistic infection (urinary/biliary/intraabdominal abcess in immunocompromised)
- can cause endocarditis, bacteremia/septicemia
- Tests: bile esculin hydrolysis (grows), growth in 6.5% NaCl (differentiate from S. bovis)
- Resistance: resistant to a ton including penicillin, vancomycin (VRE)
- Treat with 1st ampicillin + gentamycin, 2nd line vancomycin. Treat VRE with pristinamycin (dalfopristin + quinupristin) or linezolid
