Salmonella

Lab Fourteen:- ________________ Medical Microbiology
Prepared by: Luma J. Witwit

Salmonella

Gram negative bacilli, non sporing, motile by peritrichous, citrate positive, catalase (+), oxidase (-), aerogenic ( H¬2S) production, able to ferment sugar strongly and it is facultative anaerobes.

These are three types of salmonella genus:-

1- Enteric fever (typhoid fever ): S.typhi and S. paratyphi A,B,C.
2- Gastroenteritis : S.entritidis , S.typhimurium
3- Septicemia: S.cholerasuis.

Typhoid fever:
Ingestion of 104 to 108 organisms via food or drink they enough to infect by typhoid fever in human.

Specimen:
First week – blood
2-5 week – stool
3-4 week – urine

Chronic carriers mostly harbor S.typhi in the gall bladder S.typhi is found in the case.
Rarely urinary tract carriers may develop who excrete S.typhi in their urine.
Gastroenteritis , septicemia are usually acquired by contaminated foods like eggs and poultry.

Lab diagnosis:
1- Gram stain ( G- bacilli )
2- MacConkey agar(pale colonies)
3- Deoxycholate agar(DCA), Salmonella Shigella agar ( SSA) colorless with black center. DCA, SSA are selective medium for isolation of enteric pathogens ( Salmonella, shigella) with inhibition for G+ bacteria.

4- Xylose Lysine Deoxycholate agar (XLD): red with black center.
Bismuth sulfite agar: black with metallic sheen colonies, selective medium especially for the isolation of Salmonella typhi from feces, urine, sewage.
5- Selenite broth, enrichment medium for isolation of Salmonella typhi and other members of the Salmonella group from feces, urine and infected tissues.

6- Tetrathionate broth: selective liquid enrichment medium employed in the isolation of S.typhi and other member of the Salmonella which isolation from feces, urine, water.

7- TSI: K/A (H2S)+, Gas production.
8- Motility.
9- IMVC.
10- Urase (- ve )
11- Widal test for serological detection ( titers of antigens O& H )
12 - Antigen detection : Counter – immuno electrophoresis (CIE) of a single specimen of serum to detect S.typhi (O antigen) can yield early result for disease.
13 - Phage typing : Salmonella typhi has also a( Vi ) antigen, can be sub divided for useful purposes by phage typing. It is useful to diagnosis a chronic carrier of S.typhi.

Shigella:
Shigella are facultative, non motile, Gram negative bacilli. They possess the heat stable endotoxin (LPS) as characteristic of Gram-negative bacteria. Shigella are pathogenic primarily due to their ability to invasive intestinal cells, S. dysenteriae also produces a heat labile exotoxin.

Important species:
Shigella dysenteria (serogroup A) (12 serotypes)
Shigella flexueri ( serogroup B) (6 serotypes )
Shigella boydii (serogroup C) (18 serotypes)
Shigella sonnei (serogroup D) (1 serotypes)

Specimens:
Bloody, stool (bright red).
Microscopic Examination
Stool smears from patients with amebiosis should reveal erythrophagocytic trophozoites in the absence of PNM s ( polymorpho nuclear cells ), whereas bacillary dysentery is characterized by sheets of PMNs.



Laboratory diagnosis
MacConKey ( less color)
Salmonella – shigella agar(SSA): this media contain bile salts to inhibit the growth of other Gram-negative bacteria and pH indicators to differentiate lactose ferment (Coli forms) from non-lactose fomenters such as Shigella.
TSI or KIA ( Kligler iron agar ): K/A (H2S+ ) Gas production
Motility: (-)
IMVC tests.