Recovery of Salmonella bacterial isolates from pooled fecal samples from horses

It is important to determine if a horse is shedding Salmonella spp., but a complete culture series can be cost prohibitive.

Determine the optimal pooling technique to maintain high sensitivity of Salmonella spp. culture using spiked samples, and then demonstrate the efficacy of this protocol on clinical submissions.

Pooled fecal samples are as sensitive as 5 individual cultures for the detection of Salmonella shedding.

A single Salmonella-negative horse from the university herd, and 19 hospitalized horses.

Salmonella-free fecal samples were spiked with different amounts of Salmonella spp. (10² , 10³ , 10⁴ , and 10⁵ colony forming units [cfu]) and homogenized to evaluate pooled samples. Five individual fecal samples were collected from 19 hospitalized horses. Ten-gram aliquots of each individual sample were combined to make a pooled sample. Both individual and pooled samples were cultured for Salmonella spp. The identity of bacterial isolates was confirmed by matrix-assisted laser desorption-ionization time of flight mass spectrometry.

A 10²  cfu concentration of Salmonella spp. could be recovered from a spiked Salmonella-free fecal sample. Homogenization protocols indicated that the addition of 20 mL of broth to the pooled sample improved recovery, whereas homogenization time did not. Of the 19 horses tested, 5 were positive for Salmonella. In all instances, Salmonella spp. were recovered from the fecal pool as well as individual samples.

Pooling of 5 fecal samples for Salmonella culture is a sensitive and cost-effective diagnostic approach to detect horses that are shedding the organism.