Streptococcus And Others Flashcards
Streptococci
-Catalase negative, round shaped, usually in chains or pairs, oxidase negative
-Facultative anaerobes: grow best in 5-10% CO2
Enterococcus (Group D strep)
-grows in 6.5% NaCl, catalase negative but can be weakly positive because of the production of pseudo catalase, small grey colonies
-gamma hemolytic, PYR positive
Media used to isolate Strep
-blood agar
-CNA
-PEA
-Strep selective
-Can be alpha, beta, or gamma hemolytic
4 types of hemolysis associated with strep and related genera
- Gamma hemolysis: no RBC destruction, no apparent hemolysis
- Alpha hemolysis: partial RBC destruction, green/brown color around colony
- Beta hemolysis: complete RBC destruction, clear zone of hemolysis
- Alpha prime hemolysis: small zone of intact or partially lysed RBC with a zone of beta hemolysis farther into the media
Lancefield Classification system
-most beta hemolytic strep have a carbohydrate in their cell walls called a streptococcal group antigen
-Groups are: A, B, C, D, E, F, G, H….
A, C, G, cause strep throat and are identified in throat cultures
-B and F are normal flora of the throat
-Group D (Enterococcus) have technoic acid in their cell walls and is not a carbohydrate antigen
Beta Strep Group A (Strep pyogeneus)
-found in the respiratory tract and causes strep throat
-Transmission: person to person or by aerosolized droplets
-Small/grey white colonies with a zone of beta hemolysis
-PYR positive
-Pharyngitis, scarlet fever, necrotizing fasciitis
-secondary sequelae if left untreated: rheumatic fever and acute glomerulonephritis
-M protein: protein on cell surface that inhibits phagocytosis and is a major virulence factor
-Streptolysin O= lysis RBC, PMN, and platelets in absence of air (oxygen labile)
-Streptolysin S= lyses cells in presence of air (oxygen stabile)
-Growth on blood agar
-Penicillin is the treatment of choice
-Rapid strep screen lateral flow test
-Streptococcal pyrogenic exotoxins (SPE): erythrogenic toxins released and produce scarlet fever
-The bacitracin disk is no longer recommended because group C and G are also sensitive to it
-ASO test: presence of antistreptolysin O antibodies
-Anti- DNA are test is used to detect serum antibodies against strep A
Beta Strep B (Strep agalactiae)
-often found in female genital, and lower GI tract and sometimes the upper respiratory tract
-Occurs in Babies before they are born typically: causes septicemia, pneumonia, and meningitis
-Direct contact or gaining access to sterile sites
-In adults causes UTIs, septicemia, and wound infections
-On blood agar: slightly larger colonies than group A with a smaller hemolysis zone around colony,
-transluscent to opaque, flat, glossy colonies
-CAMP test positive: strep B produces CAMP factor that acts synergistically with the beta toxin produced by staph aureus and produces an arrow (its perpendicular to S. Aureus)
-Carrot broth or Todd-Hewitt broth detects genital carriage of strep B in pregnancy (rectal or vaginal swab), LIM is also used
-GeneXpert uses PCR to identify it
-Penicillin is treatment
Beta strep C, F, G
-normal skin flora, nasopharynx, GI tract, and genital tract
-F: can cause suppurative infections in people with underlying disease
-C and G: cause acute pharyngitis, some progress to glomerulonephritis
-Identified by lancefield group cell wall antigen
Strep pneumonia
-alpha hemolytic with depressed centers on blood agar due to autolytic enzyme produced (checkers) on blood agar
-Normal habitat: nasopharynx
-#1 cause of community acquired pneumonia, causes meningitis, and otitis media
-Polysaccharide capsule inhibits phagocytosis
-Meningococcal vaccine for immunocompromised
-Gram positive lancet shaped pairs
-Susceptible to optochin, greater than 15mm zone of inhibition is positive
-Bile solublility: add bile salt to colony and it will dissolve
-Most strains are sensitive to penicillin
-Virulence factor: Pneumolysin: suppresses the oxidative burst of phagocytes, which provides effective immune clearance
Viridans Streptococci
-Normal habitat: oral, respiratory, and GI mucosa
-Opportunistic pathogen
-Subacute bacterial endocarditis (SBE): indicated by multiple + blood cultures with same strep, can be lodged in an abnormal heart or heart valve
-Dental procedures can cause infection and lead to endocarditis
-PYR negative
-Strep bovis is associated with GI cancer
Enterococci (group D)
-On blood agar: small grey colonies, usually non-hemolytic
-PYR positive, salt tolerant, can hydrolyze bile esculin (black)
-UTIs, bacteremia, wound infections
-Nosocomial infection
-Treat with synergism between penicillin and aminoglycoside
-E. Faecium is more resistant and E. Faecalis is more common
-Grows in 6.5% NaCl
-A techoic acid and not a carbohydrate antigen
-Intrinsically more resistant to antibiotics than other strep
-Emerging pathogen because its resistant to Vancomycin (VRE)
-Bile Esculin +: they hydrolyze esculin in the presence of 40% bile
Abiotrophia (nutritionally deficient strep, Strep defectives)
-requires vitamin B6 for growth
-Will satellite around staph aureus
-Causes endocarditis
-Normal flora so its opportunistic (like in surgeries)
Leuconostoc
-isolated from wounds and blood and can cause septicemia and meningitis
-Intrinsically resistant to vancomycin
-PYR negative
-Produces lactic acid as a byproduct
-Known as lactic acid bacteria
Pediococcus
-intrinsically resistant to vancomycin
-Involved in human sepsis
-Produces lactic acid as a byproduct
-PYR negative
-Normal fecal flora
Rapid Strep screen for group A strep from a throat swab
-Using a tongue depressor, the provider will depress the tongue and use a long, sterile cotton swab at the back of the throat, used designated reagents A and B to extract antigens
-2 lines = positive
-Control line = negative
-Test line= inconclusive
-Nothing = inconclusive
-Blood agar is the backup
