Diagnostic and public health dilemma of lactose-fermenting Salmonella enterica serotype Typhimurium in cattle in the northeastern United States

The presence of lactose-fermenting Salmonella strains in clinical case mate rials presented to microbiology laboratories presents problems in detection and identification. Failure to detect these strains also presents a public health problem. The laboratory methods used in detecting lactose-fermentin g Salmonella enterica serotype Typhimurium from six outbreaks of salmonello sis in veal calves are described. Each outbreak was caused by a multiply-re sistant and lactose-fermenting strain of S. enterica serotype Typhimurium. The use of Levine eosin-methylene blue agar in combination with screening o f suspect colonies for C8 esterase enzyme and inoculation of colonies into sulfide-indole-motility medium for hydrogen sulfide production was particul arly effective for their detection. A hypothesis for the creation of lactos e-fermenting salmonellae in the environment is presented. It is proposed th at the environment and husbandry practices of veal-raising barns provide a unique niche in which lactose-fermenting salmonellae may arise.