SALMONELLA

SALMONELLA

Morphology
Gram – negative rodsuncapsulated (except S. typhi)unsporulatedsporulaţiPeritrichous flagella (ensure motility)

Cultural properties

Aerobe-anaerobe facultativeGrow easily on simple culture mediaOnto selective and differential media that contain biliary salts and lactose grow like lactose-negative “S” colonies.produce de H2S, colonies have a “cat-eye” appearance.

Biochemical properties

Motile, Lactose negative; acid and gas from glucose, mannitol, maltose, and sorbitol; no Acid from adonitol, sucrose, salicin, lactose ONPG test negative (lactose negative) Indole test negative Methyl red test positive Voges-Proskauer test negative Citrate positive (growth on Simmon's citrate agar) Lysine decarboxylase positive Urease negative Ornithine decarboxylase positive 2S produced from thiosulfate Phenylalanine and tryptophan deaminase negative Gelatin hydrolysis negative

TSI (Triple Sugar Iron) MIU (Motility Indole Urea). Simmons Citrate medium

Diagnosis
The diagnosis of salmonellosis requires bacteriologic isolation of the organisms from appropriate clinical specimens. Laboratory identification of the genus Salmonella is done by biochemical tests; the serologic type is confirmed by serologic testing. Feces, blood, or other specimens should be plated on several nonselective and selective agar media (blood, MacConkey, eosin-methylene blue, bismuth sulfite, Salmonella-Shigella, Hektoen agars) as well as intoenrichment broth such as selenite or tetrathionate.


The biochemical reactions of suspicious colonies are then determined on triple sugar iron agar and lysine-iron agar, and a presumptive identification is made. Biochemical identification of salmonellae has been simplified by systems that permit the rapid testing of 10-20 different biochemical parameters simultaneously. The presumptive biochemical identification of Salmonella then can be confirmed by antigenic analysis of O and H antigens using polyvalent and specific antisera. Salmonella isolates then should be sent to a central or reference laboratory for more comprehensive serologic testing and confirmation.