Prevalence and antimicrobial resistance patterns of Salmonella isolated from poultry farms

Antimicrobial agents are used in human medicine to treat infections by inhibiting the growth of bacteria. The same or similar drugs are used in in food-producing animals for therapeutic and sub-therapeutic purposes. Antimicrobial resistant bacteria that develop on farms are a public health risk as these organisms may contribute to treatment failures in infected humans. The main objective of this study was to determine the prevalence of Salmonella isolated from poultry farms in two different seasons to evaluate the effect of recommended biosecurity practices. Specifically, we identified Salmonella serotypes, measured antimicrobial resistance (AMR), and characterized AMR patterns. We hypothesized that implementing and improving biosecurity practices on poultry farms decreases Salmonella prevalence, resulting in a concurrent decrease in AMR Salmonella populations. Cloacal swabs, drag swabs, and litter samples were obtained from four different farms from the same integrator. These farms were sampled on three different days during one grow-out period during March-April (pre-recommendations season). After sampling, recommendations for improvement of the biosecurity practices were made and a second sampling was performed during October-November (post-recommendations season). Recommendations included, but were not limited to improvement of insect and rodent control, restrictions on farms visitors, restrictions on contact with poultry, and logging of entry and exit to farms. Presumptive Salmonella isolates obtained on selective agars (XLT4) were confirmed by performing PCR targeting the hilA gene. After confirmation, all positive Salmonella were serotyped and antimicrobial resistance was performed using the Sensititre™ micro-dilution system and NARMS plates. Higher Salmonella prevalence values were observed for the post-recommendations season, however, no significant differences (p>0.05) were observed between seasons. Overall, six different Salmonella serotypes were identified. S. Enteritidis was the most common Salmonella serotype followed by S. Berta and S. Mbandaka. These three Salmonella serotypes were present on all four farms. S. Typhimurium, S. Kentucky, and S. Tennessee were each found on a single farm. A total of 7% isolates exhibited antimicrobial resistance with a single isolate showing multidrug resistance. Resistance values were highest for tetracycline, nalidixic acid, and streptomycin.