Dehydrated manure from agricultural animal feedlots can become aerosolized and may potentially harbor viable antimicrobial-resistant bacteria. Little is known about the dynamics and risk of bacteria in bioaerosols originating from the feedyard environment. Nutrient deficiency, desiccation, UV exposure, temperature, and pH changes can affect bacterial viability. In this study, we investigated the impact of changes in relative humidity (RH) and UV-B exposure on enteric bacterial survival in vitro to simulate environmental conditions in cattle feedyards. Cattle manure samples were placed in two separate chambers with 73% RH and 31% RH, respectively. For the UV-B experiment, samples were placed in a chamber exposed to UV-B (treated) or in a chamber exposed to LED light (control). Samples from both experiments were spiral plated in triplicate onto selective agar media to quantify total aerobic bacteria, E. coli (total and antimicrobial-resistant (AMR)), and Enterococcus spp. (total and AMR). Results showed that enteric bacteria from cattle manure can withstand at least two stress conditions, including low RH levels and UV-B exposure. Moreover, the data revealed that antimicrobial-resistant bacteria can persist in manure under the harsh conditions that may be encountered in a feedyard environment. These findings underscore the need for mitigation strategies in feedlots to minimize the overall risk of bioaerosol formation.

Antimicrobial use in food animals selects for antimicrobial-resistant (AMR) bacteria, which most commonly reach humans via the food chain. However, AMR bacteria can also escape the feedyard via agricultural runoff, manure used as crop fertilizer, and even dust. A study published in 2015 reported AMR genes in dust from cattle feedyards; however, one of the study’s major limitations was the failure to investigate gene presence in viable bacteria, or more importantly, viable bacteria of importance to human health. Our main objective was to investigate the presence and quantity of viable bacteria and antimicrobial-resistant (AMR) determinants in fugitive bioaerosols from cattle feedyards in the downwind environment. Six bioaerosol sampling campaigns were conducted at three commercial beef cattle feedyards to assess variability in viable bacteria and AMR determinants associated with geographic location, meteorological conditions, and season. Dust samples were collected using four different sampling methods, and spiral plated in triplicate on both non-selective and antibiotic-selective media. Colonies of total aerobic bacteria, Enterococcus spp., Salmonella enterica, and Escherichia coli were enumerated. Viable bacteria, including AMR bacteria, were identified in dust from cattle feedyards. Bacteria and antimicrobial resistance genes (ARGs via qPCR) were mainly found in downwind samples. Total suspended particles (TSPs) and impinger samples yielded the highest bacterial counts. Genes encoding beta-lactam resistance (bla_CMY-2 and bla_CTX-M) were detected while the most common ARG was tet(M). The predominant Salmonella serovar identified was Lubbock. Further research is needed to assess how far viable AMR bacteria can travel in the ambient environment downwind from cattle feedyards, to model potential public health risks.

Foodborne diseases represent a link between environmental, animal, and human health interfaces from the One Health perspective. Whole genome sequencing (WGS) is becoming the gold standard in foodborne surveillance, worldwide. WGS than provides precision data from pathogens allows laboratories to resolve the genetic relations among all sources from One Health perspective, especially during outbreak investigations, getting insights into their transmission routes and pathogenicity. Salmonella spp. is the most prevalent foodborne bacteria in Colombia, in 2020, 268 foodborne outbreaks were reported to National health institute (INS) and 3079 invasive and faecal salmonellosis samples from 81% of the Colombian geographical regions. Several studies in different food sources exhibited an increase of contamination with Salmonella , a public health concern due to the steady development of antimicrobial resistance associated to specific serovars. However, integration of Salmonella spp . data including food-chain supply and clinical interfaces is very scarce in Colombia. This study carried out a national comparison of Salmonella isolates collected from food-chain supply and clinical sources. Using an epidemiological and phenotypic approach, we demonstrated the higher resolution of WGS compared with PFGE, routinely used in Salmonella surveillance in Colombia. For example, the resolution of PFGE allowed the description of two main clusters of food Salmonella Enteritidis isolates which were expanded to eight clades by using WGS. Virulence factors and antimicrobial determinant genes observed in the foodborne clades should be considered a public health concern in Colombia. WGS is a technology that provides precise and valid evidence for the establishment of dissemination routes of foodborne high-risk Salmonella clades, but it requires an integrative and continued collaboration between the stakeholders across the One Health interfaces to promote and support integrated real-time actions in public health.