Prevalence and Characterization of Salmonella enterica and Salmonella Bacteriophages Recovered from Beef Cattle Feedlots in South Texas

Abstract

Asymptomatic Salmonella carriage in beef cattle is a food safety concern, and the beef feedlot environment may function as a reservoir of this pathogen. The goal of this study was to identify and isolate Salmonella and Salmonella bacteriophages from beef cattle feedlot environments in order to better understand the microbial ecology of Salmonella and identify phages that might be useful as anti-Salmonella beef safety interventions. Three feedlots in south Texas were visited, and 27 distinct samples from each source were collected from dropped feces, feed from feed bunks, drinking water from troughs, and soil in cattle pens (n = 108 samples). Preenrichment, selective enrichment, and selective/differential isolation of Salmonella were performed on each sample. A representative subset of presumptive Salmonella isolates was prepared for biochemical identification and serotyping. Samples were pooled by feedlot and sample type to create 36 samples and enriched to recover phages. Recovered phages were tested for host range against two panels of Salmonella hosts. Salmonella bacteria were identified in 20 (18.5%) of 108 samples by biochemical and/or serological testing. The serovars recovered included Salmonella enterica serovars Anatum, Muenchen, Altona, Kralingen, Kentucky, and Montevideo; Salmonella Anatum was the most frequently recovered serotype. Phage-positive samples were distributed evenly over the three feedlots, suggesting that phage prevalence is not strongly correlated with the presence of culturable Salmonella. Phages were found more frequently in soil and feces than in feed and water samples. The recovery of bacteriophages in the Salmonella-free feedlot suggests that phages might play a role in suppressing the Salmonella population in a feedlot environment.

Population Dynamics of Salmonella enterica within Beef Cattle Cohorts Followed from Single-Dose Metaphylactic Antibiotic Treatment until Slaughter

“…The ecology of Salmonella within cattle populations is clearly far more complex than a simple fecal-oral mode of transmission, supporting the idea that origin/source and other ambient environmental factors are likely to be involved (49)(50)(51)(52). One of the limitations of this study was that prior environmental samples were not collected and analyzed to determine the contributions of preexisting soil microbiota in the feedlot pens, other animals (birds and pests) that had contact with the cattle, feedlot equipment, and bacteriophages in the environment (53,54). Therefore, the environmental factors that influenced the temporal dynamic selection of dominant serotypes of Salmonella among pens and cattle remain unclear.…”

Development and Validation of a Microtiter Plate-Based Assay for Determination of Bacteriophage Host Range and Virulence

“…Phage FelixO1 was obtained from the Salmonella Genetic Stock Center (University of Calgary, Calgary, AB, Canada) and propagated on the S. Typhimurium strain LT2. Twelve of the phages used in this study were isolated in 2014 from a set of 72 phage-enriched beef feedlot environmental samples described previously [ 37 ]. The 72 enrichments were pooled by pen, feedlot, and enrichment strains to produce 18 composite samples and enriched again against the same two sets of mixed bacterial hosts, which was described previously [ 37 ].…”

“…Twelve of the phages used in this study were isolated in 2014 from a set of 72 phage-enriched beef feedlot environmental samples described previously [ 37 ]. The 72 enrichments were pooled by pen, feedlot, and enrichment strains to produce 18 composite samples and enriched again against the same two sets of mixed bacterial hosts, which was described previously [ 37 ]. Two additional phages known as Sw2 and Melville were isolated in 2016 from a municipal wastewater influent sample enriched for phage using the same mixed-host panel as above.…”

Interactions of Organic Acids with Salmonella Strains from Feedlot Water-Sprinkled Cattle

“…Therefore, the acid wash step should be studied. Recently, the Salmonella serovars Anatum, Montevideo and Kentucky were identified in cattle feces during a study to determine the prevalence of Salmonella enterica in South Texas beef cattle feedlots [29]. These Salmonella serovars are among the top 10 Salmonella serovars isolated from commercial ground meat [7], and can be important players in outbreaks of foodborne illness [8-10, 21, 22].…”