Streptococcus pyogenes
Gram + strepto- or diplo-cocci. Catalase negative. Beta-hemolytifc. Causes strep throat, Scarlet fever, Rheumatic fever, and Necrotizing fasciitis.
What virulence factors does Streptococcus pyogenes have?
Streptolysin O: lyses blood cells; similar to alpha-hemolysin. Pyrogenic exotoxin: superantigen and Streptokinase: dissolves fibrin clots.
Superantigens from Pyrogenic exotoxins
Exhibit inappropriate MHC-II binding to CTLs. Non-selective T-cell activation leads to massive, systemic inflammatory response.
Streptokinase dissolves fibrin clots to do what?
Helps S. pyogenes to spread systemically by dissolving fibrin clots.
What is Necrotizing fasciitis?
Flesh-eating bacteria with a 20-80% fatality rate. Common in immunocompromised patients, diabetics and alcoholics.
Citrate Test
Tests the ability to use citrate as a sole carbon source. Since citrate test examines bacterial growth, heavy inoculation can skew results.
Positve and Negative Citrate Tests
Turn blue. Tested Enterobacter aerogenes and Escherichia coli. E. aerogenes was blue/positive and E. coli was green/negative.
To perform a Citrate Test
Inoculate bacteria on Simmons citrate slants.
Decarboxylation Test
Tests the ability Ability to remove a carboxyl group C.O.O.H. and increase p.H. of the environment. p.H.indicator is brom cresol purple.
Decarboxylation Tests are performed using 3 kinds of broth, what are they?
Lysine, Ornithine and Arginine decarboxylase broths. Then cover with an overlay of mineral oil.
Which bacteria did we test when we performed the Decarboxylation Tests in lab?
Serratia marcescens, Shigella flexneri and Salmonella typhimurium. S.marcescens was light purple/positive for Lysine, dark purple/positive for Ornithine and grey/light purple for Arginine.
S. flexneri was yellow/negative for Lysine, clear/grey/negative for Ornithine, and purple/positive for Arginine.
S. typhimurium was clear/negative for Lysine, yellow/negative for Ornithine and positive/purple for Arginine.
Positive Decarboxylation Test are purple.
Anything besides purple, means the Decarboxylation Test was negative.
S.I.M Test
Tests the ability to reduce sulfur, produce indoles from tryptophan catabolism, and be motile. Tested P. vulgaris and E. coli.
To complete a S.I.M. Test
Add 2 drops of Kovac's reagent into the tubes. Black = H2S sulfur reduction. Pink = indoles. Motility = growth outside the stab line.
S.I.M. Test of P. vulgaris and E. coli.revealed
P. vulgaris was clean on top = no indoles and black = H2S production. E. coli. was pink on top = indoles and black = H2S production.
T.S.I - Triple Sugar Iron Test
Tests the ability of of Gram negative enteric bacteria to ferment triple sugars and reduce sulfur.
T.S.I. is composed of
Glucose, lactose, sucrose; sodium thiosulfate; phenol red is the color indicator. Tested P. aeruginosa, P. vulgaris, S. typhimurium and E. coli.
Positive T.S.I. Test is
Yellow = acid production from sugar fermentation. Black precipitate = H2S reduction.
Red = _________.
Motility Test
Tests the ability to "swim away" from stab line. Contains triphenyltetrazolium chloride T.T.C. Tested E. aerogenes and K. pneumoniae.
Positive Motility Test
Most enteric bacteria are capable of reducing T.T.C. Growth away from the stab line = positive motility test.
Motility test for E. aerogenes was _________.
Motility test for K. pneumoniae was _________.