Characterization of Listeria monocytogenes isolates from Jersey cattle in Wisconsin and their impact on fecal microbial communities

Abstract

L. monocytogenes is one of the major sources of microbial contamination in food products. The ecology and transmission model of L. monocytogenes have been widely studied, where persistence of L. monocytogenes in the farm environment is contributed by fecal shedding. Lately, studies have provided evidence supporting this model by demonstrating strong genetic correlations between clinical isolates and dairy products. However, the relationship between asymptomatic carriage of L. monocytogenes and gastrointestinal tract (GI) microbial communities has not been reported. In this study, a 29-day longitudinal survey was designed to collect L. monocytogenes isolates from fecal and feed samples at a dairy farm in Wisconsin. We found that 90% (18/20) of the animals had shedded Listeria with 70% (14/20) of the animals shedding over a period of 3 – 5 days, indicating there was a high prevalence of L. monocytogenes carriage among the group of 20 jersey cattle. A total of 44 L. monocytogenes fecal isolates were obtained from the survey, where they were screened for i) antibiotic susceptibility using broth microdilution assays and ii) virulence potential using murine and human epithelial cell lines. The majority of isolates were resistant to ampicillin (43/44), and half of them were resistant to gentamicin and trimethoprim/sulfamethoxazole. Many isolates also displayed enhanced intracellular growth in murine fibroblast cells (33/44), where eight of those are significantly more invasive when compared against 10403S in Caco-2 cells, suggesting that they are capable of causing systemic infection. We found that subclinical carriage of L. monocytogenes did not alter overall microbiota community in the gut between shedders and non-shedders by examining a small number of cattle from the group (n = 6). However, this pathogen significantly changed the relative abundances of certain operational taxonomic units within the Bacteroidetes and Firmicutes phyla, highlighting its potential negative impacts on animal gut health.