GENOTYPIC AND PHENOTYPIC ANALYSIS OF SALMONELLA STRAINS ASSOCIATED WITH AN OUTBREAK OF EQUINE NEONATAL SALMONELLOSIS

Isolates of Salmonella choleraesuis serotype ohio (S. ohio) recovered during an outbreak of equine neonatal salmonellosis on a Thoroughbred farm were compared with isolates of the same serotype from various ani mal, feed and environmental sources. Biochemical profiles, antimicrobi al susceptibility patterns, phage susceptibility, plasmid profiles, re striction endonuclease analysis and ribotyping were used to compare re latedness of the strains. A total of 46 outbreak and non-outbreak asso ciated isolates of S. ohio were studied. Differences in antimicrobial susceptibility patterns, phage susceptibility and plasmid profiles wer e useful for differentiating outbreak isolates from other equine isola tes as well as bovine, porcine and some poultry isolates. Feed and oth er poultry isolates, most in geographic proximity to the outbreak, wer e indistinguishable from outbreak isolates by any of the methods emplo yed. Investigative studies on the farm along with results of genotypic and phenotypic analysis of isolates suggested that contaminated feed was the most likely source of Salmonella in this outbreak.