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Unit 2 Chapter 15

Streptococcus , Enterococcus , and Other Catalase-Negative Gram-Positive Cocci

General characteristics of streptococcus and Enterococcus catalase-negative, gram-positive cocci; arranged in pairs or chains; can behave like facultative anaerobes
S. pyogenes *colony morphology* β-hemolytic, nonmotile, encapsulated, facultatively anaerobic,
S. pyogenes *gram stain results* Gram-positive coccus
S. pyogenes *testing results* ferments lactose, salicin, and trehalose but not inulin, mannitol, raffinose, fibose, or sorbitol; hydrolyzes arginine and PYR, but not hippurate
S. pyogenes *virulence factors* Mprotein, encoded by genes emm; fibronectin-binding protein; lipoteichoic acid; hyaluronic acid capsule; and extracellular products
S. pyogenes *epidemiology* nose, throat, and skin are reservoirs transmitted by direct person to person contact or by contaminated aerosols
S. pyogenes *infections* bacterial pharyngitis, pyodermal infections( impetigo, erysipelas, cellulitis, scarlet fever), necrotizing fasciitis, streptococcal toxic shock syndrome, poststreptococcal sequelae (rheumatic fever, acute glomerulonephritis)
S. agalctiae *colony morphology* group B-specific antigen, acid stable polysaccharide located in the cell wall; there are nine recognized capsular polysaccharide serotypes; detected by precipitin tests
S. agalctiae *gram stain results* occasional isolates are found that are nonhemolytic; β-hemolytic, Group B strep
S. agalctiae *testing results* Gram + stain of CSF, urine, blood ß-Hemolytic Lancefield Group: B bacitracin resistant CAMP test - synergy between hemolysin of GBS and ß-hemolysin of S. Aureus
S. agalctiae *virulence factors* Capsule: polysaccharide, C5a peptidase: Spreading Factors: DNAases, Hyaluronidase:
S. agalctiae *epidemiology* Larger colonies, narrower Beta-hemolysis zone;Normal flora, cervicovaginal canal and URT/ GI tract; Major agents of septicemias and meningitis in newborns, highest incidence associated with prolonged/difficult deliveries/premature births.
S. agalctiae *infections* neonatal sepsis, meningitis, puerperal fever, pyogenic infections
Group C and G Strep *colony morphology* large-colony: isolates with group C and G, forming β-hemolyticisolatesbelong to subspecies; small colony:
Group C and G Strep *gram stain results* Gram-positive
Group C and G Strep *testing results* Less than 1% of all bacteremias
Group C and G Strep *virulence factors* blood culture isolates that exhibit group A or L antigens
Group C and G Strep *epidemiology* invasive
Group C and G Strep *infections* upper respiratory tract infections, skin infections, soft tissue infections, invasive infections such as NF, glomerulonephritis and rheumatic fever after infection
S. pneumoniae *colony morphology* α-hemolytic, nonmotile, encapsulated, facultatively anaerobic
S. pneumoniae *gram stain results* gram-positive coccusi pairs
S. pneumoniae *testing results* negative for arginine hydrolysis, esculin hydrolysis, and acid production from mannitol and sorbitol. Urese and Voges-Proskauer negative and susceptible to optochin.
S. pneumoniae *virulence factors* capsular polysaccharide
S. pneumoniae *epidemiology* susceptible populations; superficial URT infection in infants and children; invasive infections in very young, elderly, anyone with an underlying disease such as chronic alcoholism, stroke, asplenia, or prior respiratory disease
S. pneumoniae *infections* pneumonia, sinusitis, otitis media, bacteremia, and meningitis
Draw and/or explain the schema to ID strep/enterococcus Gram-positive, facultatively anaerobic cocci Most are typically spherical; some may appear elongated; Appear in chains when smears are prepared from broth cultures Catalase-and oxidase-negative
Enterococcus 2 most common species *colony morphology* gram positive coccithat are natural inhabitants of the intestional tracts of humans and animals: E. faecalis and E. faecium are most commonly identified; others are E.durans, Eavium, E. casseliflavus, E. gallinarium, and E. raffinosus
Enterococcus 2 most common species *gram stain results* nonhemolytic or α-hemolytic, some may show β--hemolysis;
Enterococcus 2 most common species *testing results* may exhibit a pseudocatalase reaction; weak bubbling with a catalase test. Other species identified based on biochemical characteristics; hydrolizes PYR
Enterococcus 2 most common species *virulence factors* incompletely understood; can grow in extreme conditions and are resistant to multiple antimicrobial agents
Enterococcus 2 most common species *epidemiology* Habitat: mucous membrane, oval/GI/GU/RT. Component of normal GI flora
Enterococcus 2 most common species *infections* nosocomial infections: UTI followed by bacteremia
List the Streptpcoccus-like organisms Aerococcus, Gemella, Lactococcus, Leuconostoc, and Pediococcus; Abiotrophia and Granulicatella
Define Lancefield classification based on extraction of C carbohydrate from the streptococcal cell wall by placing the organisms in dilute acid and heating for 10 minutes
CAMP test *principle* presumptive identification of GBS
CAMP test *medium* sheep blood agar plate
CAMP test *reporting results* Positive result= arrowhead-shaped area of enhanced hemolysis where the two streaks approach each other; negative results = no enhanced hemolysis
CAMP test *additional* performed in 3 ways: by using β-lysin producing strain of S. aureus, another is with the use of a disk impregnated with the β-lysin, a rapid form involves placing a drop of extracted β-lysin on the area of confluent growth of suspected GBS
Hippurate Hydrolysis *principal* used to differentiate S. agalactiae from other β-hemolytic streptococci
Hippurate Hydrolysis *reagents* sodium hippurate 1%, Ninhydrin
Hippurate Hydrolysis *result reporting* positive: S. agalactiae; negative: S. pyogenes
Hippurate Hydrolysis *additional* positive results = deep purple color that indicates hippurate hydrolysis; negative results = no color or very slight purple color
PYR Hydrolysis *principle* PYR-impregnated disks serve as the substrate to produce α-naphthylamide, which is detected in the presence of D-dimethylaminocinnamaldehyde (DMCA) by the production of a red color
PYR Hydrolysis *controls* positive: Enterococcus faecalis; negative: Streptococcus agalactiae
PYR Hydrolysis *result reporting* positive result = red color; negative result = colorless
PYR Hydrolysis *additional* purpose: to differentiate gram-positive cocci that will hydrolyze the substrate L-pyrrolidonyl α-naphthylamide (PYR) from those that are PYR-negative
Voges-Proskauer test *principle* used to distinguish the small colony forming β-hemolytic anginosus group contaminating groups A or C antigens from large colony forming pyogenicstrains with the same antigens
Voges-Proskauer test *reagents* 2mL of VP broth, 5% α-naphthol an 40% potassium hydroxide
Voges-Proskauer test *result reporting* positive = formation of red or pink color members of the antigenosus group are positive
Bile Esculin *principle* Group D streptococci and enterococci grow in the presence of bile and also hydrolyze esculin to esculetin and glucose. Esculetin diffuses into the agar and combines with ferric citrate in the medium to produce a black complex
Bile Esculin *media and specimen* specimen: isolated colonies of test organism on sheep blood agar; media: bile esculin agar
Bile Esculin *result reporting* positive result = blackening of agar; negative result = no blackening of the agar (growth doesn't indicate a positive result)
Bile Esculin *additional* positive: Group D streptococci; negative: S. pyogenes or viridans streptococci
Salt Tolerance *principle* Enterococcus, Aerococcus, and some species of Pediococcus and Leuconostoc can withstand a higer salt concentration than other gram-positive cocci
Salt Tolerance *specimen and medium* specimen: isolated colonies of test organism on sheep blood agar; medium : 6.5% NaCl broth, nutrient broth base
Salt Tolerance *result reporting* positive result = turbidity; negative result = no turbidity
Salt Tolerance *additional* positive: Enterococcus; negative: S. pyogenes or viridans streptococci
Optochin suseptibility *principle* Optochin sensitivity allows for the presumptive identification of alpha-hemolytic streptococci as S. pneumoniae, although some pneumococcal strains are optochin-resistant. Other alpha-hemolytic streptococcal species are optochin-resistant
Optochin suseptibility *reagents* Intereferes with the production of ATP -S.pneumoniae has a >=14mm zone of inhibition
Optochin suseptibility *result reporting* Positive: Zone of inhibition is 14 mm or greater in diameter with 6 mm disk; Negative: No zone of inhibition Equivocal: Any zone of inhibition less than 14 mm is questionable for pneumococci
Optochin suseptibility *additional* Each new lot of optochin disks should be tested with positive and negative controls. Positive: Growth of S. pneumoniae strain ATCC 49619 is inhibited by optochin Negative: Growth of S. mitis strain ATCC 49456 is not inhibited by optochin.
Created by: luceroapril