Salmonella spp.

Lab 6

Prepared bySamira Fattah

Assis. Lec.College of health sciences-HMU

General character

•  rod-shaped bacteria•  gram-negative.• have peritrichous flagella .• Non-lactose fermenting.• Facultative anaerobes• H2S producing

Laboratory diagnosis

• Specimen:1. for enteric fever.

•  Blood.•  Bone marrow.• Stool.•  urine.• Serum

2. for gastroenteritis. • Stool

For enteric fever

•  Blood – 80% positive in the first  week.•  Stool- 70-80% positive in the second and third week.• Urine- 20% positive in the third and fourth week.• Serum for widal test- positive  after the second week of 

illness.

• Gram stain    Gram-negative rod-shaped bacterium 

On Culture media

On MacConkey agar

•  The bacteria do not ferment lactose, the colonies  growth appear colorless and the agar surrounding the bacteria remains relatively transparent.

On EMB

• Because Salmonella        

    species do not ferment lactose or produce acid, their colonies appear grey on EMB agar.

On Salmonella Shigella Agar

•  is used for the isolation of Salmonella spp. and some strains of Shigella spp.

•  inhibit gram-positive bacteria, most coliform bacteria, and inhibit swarming Proteus spp., while allowing Salmonella spp. to grow. 

Salmonella will not ferment lactose, but do produce hydrogen sulfide gas.  The resulting bacterial colonies will appear colorless with black centers.

On Xylose lysine deoxycholate agar

• Salmonella metabolise thiosulfate to produce  hydrogen sulfide, which leads to the formation of colonies with black centers and allows them to be differentiated from the similarly coloured Shigella colonies.

Motility test

• salmonella is motile; see the fuzzy pink color which is radiating out from the stab line.

Biochemical reactions

Biochemical test Result

  Oxidase test                             -

  Catalase test                            +                     Indole                                    -                            Citrate                                 +

         Voges - Proskauer                  -

          H2S production                     +

API test

• Api-20E result for Salmonella sp.

Serological test(widal test):

Used to determine antibody titers in patients against antigens from salmonella species.