The rapid emergence of antibiotic resistance (AR) is a major public health concern. Recent findings on the prevalence of foodborne antibiotic resistant (ART) commensal bacteria in ready-to-consume food products suggested that the food chain likely serves as a major avenue disseminating ART bacteria to the human hosts through daily food intake. To properly assess the impact of antibiotics and the food chain on AR development in hosts and to develop effective mitigation, this study examined 1) the baseline of AR in human gastrointestinal (GI) tract system using multiple infant subjects without antibiotic exposure, 2) prevalence of ART bacteria in non-food animals, and 3) the impact of foodborne ART bacteria on AR ecology in GI tract using a murine model. In addition, a small scale study was conducted to examine the prevalence of AR in representative aquaculture products and production environment to assess the potential impact of aquaculture practices on the development of ART bacteria, and the susceptibility of ART bacteria to conventional cooking methods.
The first part of the study examined gut microbiota of 6 infant subjects from newborn to 1 year of age, fed on breast milk and/or infant formula during early stage of development and without prior exposure to antibiotics. Predominant bacterial populations resistant to several antibiotics and multiple resistance genes were found in the infant GI tracts within the first week of age. Several ART population transitions were also observed in the absence of antibiotic exposure and dietary changes. The data suggested that the early development of AR in human gut microbiota is independent of infants’ exposure to antibiotics, and that ART population is significantly amplified within the host even in the absence of the antibiotic selective pressure.
The study also investigated the prevalence of AR in non-food animals using 7 pets and 13 zoo animals. It was found that ART bacteria and AR gene pool were prevalent in many animals examined, some of which were never exposed to growth promoter or antibiotic treatment. The finding suggested that non-food animals might be an important component in AR circulation. Most importantly, antibiotic application is not the essential contributing factor leading to prevalence of ART bacteria in the hosts.
The study further evaluated the capability of foodborne ART bacteria in colonizing host GI tract using two foodborne ART strains. It was found that foodborne ART bacteria colonized and amplified in mouse GI tract in up to 109 CFU/g in the presence of human associated microbiota, and persisted for up to 2 months after withdrawn of the ART bacteria influx and in the absence of the corresponding antibiotics.
The study finally surveyed the prevalence of AR in representative fish, shrimp and environmental samples from aquaculture production, and raw seafood products from local markets for a preliminary understanding of potential critical control points for AR mitigation in aquaculture production. It was found that ART bacteria and AR gene pools were prevalent in most samples analyzed. Household cooking methods, including boiling, stir frying, steam and barbecue, were effective as AR mitigation practice.