The Enterobacteriaceae are generally divided into 2 groups based upon their ability to ferment the sugar?
Characteristics for presumptive ID for Enterobacteriaceae; *Glucose; Oxidase; Nitrate reduction; Catalase
Glucose (++); Oxidase (--); Nitrate reduction (++)**; Catalase (++)
The exception for Nitrate reduction are?
Certain Enterobacter (Pantoea) agglomerans and some Serratia and Yersinia species
Components of TSI
Protein derivatives for enrichment, glucose, lactose, sucrose, ferrous sulfate, and phenol red indicator.
Glucose fermented, lactose not fermented, hydrogen sulfide produced
Alkaline slant/ acid deep (black) (K/A/H2S)
MacConkey Agar (MAC)
Bile salts and crystal violet inhibt gram- positive organisms. Lactose is the only carbohydrate. Neutral Red indicator
MacConkey positive and negative look like?
Bright pink colonies are Lactose positive; Colorless colonies are lactose negative
Eosin-Methylene Blue (EMB)
Dyes inhibit Gram-positivew organisms and are indicators of lactose fermentation E.coli exhibits a green metallic sheen, lactose fermenters are blue-violet, and non-lactose fermenters are transparent or colorless.
Salmonella Shigella Agar (SS)
Selective; Inhibits most coliforms due to bile salts and sodium citrate. Sodium thiosulfate is added as sulfur source and ferric ammonium sulfate for detection of H2S. Lactose is sole carbohydrate added with neutral red pH indicator.
Hektoen Enteric Agar (HE)
Increaes yield of Salmonella and Shigella from heavy concentrations of normal fecal flora. Significant ingredients include high bile salts concentration, lactose, sucrose, sodium thiosulfate and ferric ammonium sulfate used for H2S detection and acid fuschin-bromthymol blue for pH indicator.
Xylose Lysine Deoxycholate (XLD)
Less inhibitory than HE. Contains xylose, lactose, sucrose for acid production and phenol red indicator. Lysine is used to detect Salmonella species. Hydrogen sulfide detection is similar to compoinetns in HE.
Fermenters produce acid from lactose; pH indicator. Non-fermenters lack enzymes to metabolize lactose
Hydrogen Sulfide production
Reacts with sulfure-containing amino acids in the media and H2S combines with the iron-based detector--> black ppt.
The ability to liberate sulfur from sulfur containing amino acids or other compounds.
Degradation end product from the metabgolism of the amino acid tryptophan by bacteria which produce the enzyme tryptophanase. Spot or tube test. RED= POS/ YELLOW= NEG.
Methyl Red (MR) test
Bacteria that utilize pyruvate (glucose) produce a lot of mixed acid during fermentation. INCUBATION TIME IS IMPORTANT & KEY. 48 hours. Detects the mixed acids. RED=POS/ NO COLOR= NEG.
Voges Proskauer Test (VP)
Used to detect the formation of acetylmethyl carbinol (acetoin) as a product of glucose fermentation. Detects the end product of acetoin during pyruvate (glucose) utilization.
Requires O2; the organisms capability to turn the medium alkaline as they grow. Bromthymol blue is teh pH indicator.
Organisms possessing the enzyme Urease can hydrolyze urea in the media releasing ammonia as an end product. Hydrolysis of urea causes an alkalization of the medium and the pH indicator phenol red causes a HOT PINK color to form in the media= POSITIVE!
Decarboxylation of Ornithine, lysine, and arginine (all amino acids)
Many bacteria remove the carboxyl group (COOH) from an amino acid to form an alkaline reacting amine. Detects alkaline pH (pH indicators bromcresol purple and cresol red) shift in the medium.
Phenylalanine Deaminase Test
Certain bacteria area capable of deaminating phenylalanine (amino acid) with the formation of phenylpyruvic acid. Phenylpyruvic acid is detected by adding ferric chloride to the medium.