Culturing Feces For Salmonella:
Special Considerations
 Equine*

*NOTE:  Most of these considerations also apply to other species.

Indications for performing this test:  Culturing of feces for Salmonella is indicated when a horse shows signs compatible with the disease, either the acute form (including profuse diarrhea, colic, depression, anorexia) or the chronic form (weight loss, soft feces, dehydration).


This foal suffering from colic may have Salmonella

The Procedure:  Culturing is typically performed with large quantities of feces (between 5 and 30 grams) to maximize the chances of finding the organism.  The more solid the fecal material cultured, the more likely Salmonella organisms will be detected.  The best results come from indirect isolation, when feces is first prepared for culture by short-term incubation in a selective media such as selenite or tetrathionate broth, then later plated on brilliant green, Salmonella Shigella, or XLD agar.  Direct isolation involves the placement of the fecal material straight onto the agar.  After incubation, the plates are examined for the presence of Salmonella organisms. 

Salmonella on SS agar Salmonella species grown in broth


Notes on Culturing:  Because the sensitivity of Salmonella culture is only 30-50%, and because a horse can test positive for Salmonella, become negative, then revert again to positive status, it is generally agreed upon that a horse must have a minimum of five consecutive Salmonella-negative fecal cultures before being considered not to have salmonellosis.  It has been hypothesized that Salmonella species are difficult to culture because they are shed intermittently, they may be less viable due to sub-lethal damage by the host's immune system, or they are weakened prior to culturing by the antimicrobials most infected horses have been given.   The sensitivity of fecal cultures for salmonella can be increased to 60-75% by concurrently culturing an intestinal biopsy specimen.


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