Conjugative transfer of plasmid-located antibiotic resistance genes within the gastrointestinal tract of lesser mealworm larvae, Alphitobius diaperinus (Coleoptera: Tenebrionidae)

Authors: Crippen, Tawni - Tc; Poole, Toni

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2009
Publication Date: 4/20/2009
Citation: Crippen, T.L., Poole, T.L. 2009. Conjugative transfer of plasmid-located antibiotic resistance genes within the gastrointestinal tract of lesser mealworm larvae, Alphitobius diaperinus (Coleoptera: Tenebrionidae). Foodborne Pathogens and Disease. 6:907-915.

Interpretive Summary: Bacteria that cause disease in humans and animals are becoming increasingly resistant to antibiotics. The role of the food animal industry and of human medicine in the production of resistant bacteria is unclear. Poultry producers are very concerned with maintaining healthy birds and limiting the presence of disease-causing bacteria on retail chicken products. Unfortunately, unwanted insects are a common occurrence in facilities where poultry are raised. One of the most abundant insect species is the lesser mealworm. All life stages of this insect can be found inhabiting and feeding within the litter of commercial poultry operations. Lesser mealworm beetles can carry agents of disease, such as bacteria and viruses. Insects that can carry bacteria are particularly troublesome because there is a potential site for the transfer of antibiotic resistance genes between bacteria associated with the insect. This study investigated whether the transfer of antibiotic resistance genes could occur within the gut of the larvae of the lesser mealworm. The final results showed that antibiotic resistance gene transfer occurred at a high level between Salmonella and E. coli in the gut of the larvae of the lesser mealworm. There are many things to consider when trying to minimize pathogens within a poultry facility. All reservoirs which harbor agents capable of passing on antibiotic resistance genes must be identified so that control measures can be instituted. This study established the lesser mealworm as a potential agent assisting in the transfer of antibiotic resistance genes within the poultry production facility.

Technical Abstract: The frequency of conjugative transfer of antimicrobial resistance plasmids between bacteria within the gastrointestinal tract of lesser mealworm larvae, a prevalent pest in poultry production facilities was determined. Lesser mealworm larvae were exposed to a negative bacterial control (PBS), a donor Salmonella enterica serotype Newport strain, a recipient Escherichia coli, or both donor and recipient to examine horizontal gene transfer of plasmids. Horizontal gene transfer was validated via a combination of selective culturing, testing of indole production by spot test, characterization of incompatibility plasmids by PCR, and profiling antibiotic susceptibility by a minimum inhibitory concentration (MIC) assay. Transconjugants were produced in all larvae exposed to both donor and recipient bacteria at frequencies comparable to control in vitro filter mating conjugation studies run concurrently with the in vivo larval study. Transconjugants displayed resistance to seven antibiotics in our MIC panel and when characterized for incompatibility plasmids, were positive for the N replicon and negative for the A/C replicon. The transconjugants did not display resistance to expanded-spectrum cephalosporins which were associated with the A/C plasmid. This study demonstrates that that lesser mealworm larvae, which infest poultry litter, are capable of supporting the horizontal transfer of antibiotic resistance genes and that this exchange can occur within their gastrointestinal tract and between different species of bacteria under laboratory conditions. This information is essential to science-based risk assessments of industrial antimicrobial usage and its impact on animal and human health.