Population dynamics of Salmonella enterica within beef cattle cohorts followed from single-dose metaphylactic antibiotic treatment until slaughter

Authors: LEVENT, GIZEM - Texas A&M University; SCHLOCHTERMEIER, ASHLYNN - West Texas A & M University; IVES, SAM - West Texas A & M University; NORMAN, KERI - Texas A&M University; LAWHON, SARA - Texas A&M University; LONERAGAN, GUY - Texas Tech University; Anderson, Robin; VINASCO, JAVIER - Texas A&M University; SCOTT, HARVEY - Texas A&M University

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2019
Publication Date: 12/1/2019
Citation: Levent, G., Schlochtermeier, A., Ives, S.E., Norman, K.N., Lawhon, S.D., Loneragan, G.H., Anderson, R.C., Vinasco, J., Scott, H.M. 2019. Population dynamics of Salmonella enterica within beef cattle cohorts followed from single-dose metaphylactic antibiotic treatment until slaughter. Applied and Environmental Microbiology. 85(23):e01386-19. https://doi.org/10.1128/AEM.01386-19.
DOI: https://doi.org/10.1128/AEM.01386-19

Interpretive Summary: Antibiotic use in cattle may select for multidrug-resistant bacteria such as the foodborne pathogen Salmonella enterica, which is considered a serious threat to humans by the U.S. Centers for Disease Control and Prevention. To study the potential effects of two commonly used antibiotics, ceftiofur and tulathromycin, on Salmonella distribution among cattle, we sampled their feces, lymph nodes, and hide and cultured these using standard microbiological methods. We also conducted a new and sensitive whole genome sequencing method to determine differences between the Salmonella that were isolated. Our results revealed no significant effects of antibiotic treatments on prevalence or quantity of Salmonella in the later feeding period and at slaughter. Moreover, most of the Salmonella isolates were susceptible to a panel of 14 commonly used antibiotics before and after treatment. However, there was a significant period effect observed, with prevalence and quantity of Salmonella increasing from spring through mid-summer months. Also, there was a significant effect of where the animals were raised. These results help us to understand the factors affecting the spread and distribution of Salmonella during rearing and slaughter and will ultimately help producers and processors develop technologies to reduce risks of food from infected animals entering into the food chain, thereby improving the microbiological safety of meat and milk available to the American consumer.

Technical Abstract: Antibiotic use in cattle may select for multidrug-resistant Salmonella enterica, which is considered a serious threat by the U.S. Centers for Disease Control and Prevention. A randomized controlled longitudinal field trial was designed to determine the long-term effects of two antibiotics (ceftiofur and tulathromycin) on Salmonella distribution among cattle feces, peripheral lymph nodes, and hide samples. One hundred thirty-four beef cattle were divided among 12 pens, with cattle in each of the three-pen blocks receiving either ceftiofur, tulathromycin, or no antibiotic (control). Fecal samples were collected before treatment (Day 0) and following treatment on Days 7, 14, 28, 56 and at slaughter. Hide samples were collected on the day before slaughter, and lymph nodes were collected from carcasses at slaughter. Salmonella was isolated and quantified using standard microbiological methods. The microbroth dilution method was used to determine phenotypic antimicrobial susceptibility. Whole genome sequencing (WGS) was used to determine serotypes. Data indicated no significant effects (P greater than 0.05) of metaphylactic antibiotic treatments on prevalence or quantity of Salmonella in the later feeding period and at slaughter. However, there was a significant period effect observed with prevalence and quantity increasing from spring through mid-summer months (P less than 0.05). The majority of Salmonella isolates were pansusceptible to a panel of 14 antibiotics before and after treatment. Highly prevalent Salmonella serotypes were determined to be S. Montevideo, S. Anatum, S. Cerro and S. Lubbock across all sample types. Strong pen and origin effects were observed regarding which Salmonella serotypes originated from fecal, lymph node, and hide samples.