Purpose: To determine the prevalence, serovars and phenotypic AMR status of Salmonella from a range of cattle classes.
Methods: A total of 1500 fecal samples from adult beef (628), young beef (286), adult dairy (128), young dairy (143) and veal calves (315) were tested for Salmonella using a Dynabead IMS protocol. The resulting Salmonella isolates were serotyped using molecular and conventional serotyping methods and were subsequently phenotypically assessed for resistance to 17 antimicrobials using microbroth dilution and the Sensititre apparatus.
Results: Salmonella were isolated from 65 (10.4%) adult beef, 39 (13.6%) young beef, 23 (18.0%) adult dairy, 44 (30.8%) young dairy and 45 (14.3%) veal calves. Thirty-seven Salmonella serovars were identified with Typhimurium comprising between 20 and 50% of isolates across each of the cattle classes. Anatum, Bovismorbificans and Saintpaul were the only other serovars present in > 10% of isolates in any cattle class. Greater than 96% of all isolates were susceptible to all antimicrobials tested. AMR was only observed in isolates from beef cattle and were to antimicrobials of low importance to human medicine.
Significance: Although some differences in prevalence and AMR between cattle classes were observed, there is minimal evidence that specific production practices are responsible for disproportionate contributions to AMR development and in general resistance to antimicrobials of critical and high importance in human medicine was low regardless of the isolate source.