Conjugative plasmid transfer between Salmonella enterica Newport and Escherichia coli within the gastrointestinal tract of the lesser mealworm beetle, Alphitobius diaperinus (Coleoptera: Tenebrionidae)

Authors: Poole, Toni; Crippen, Tawni - Tc

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2009
Publication Date: 8/30/2009
Citation: Poole, T.L., Crippen, T.L. 2009. Conjugative plasmid transfer between Salmonella enterica Newport and Escherichia coli within the gastrointestinal tract of the lesser mealworm beetle, Alphitobius diaperinus (Coleoptera: Tenebrionidae). Poultry Science. 88:1553-1558.

Interpretive Summary: Bacteria that cause disease in humans and animals are becoming increasingly resistant to antibiotics. This has caused public health concern because diseases once thought eradicated are reappearing. Bacteria are not only becoming resistant to one or two antibiotics, they are becoming resistant to many antibiotics; such bacteria are called multi-drug resistant bacteria. Many public health officials blame the food animal industry for the emergence of multi-drug resistant bacteria and down play the role of human medicine. Poultry producers have long been under pressure to limit the presence of disease-causing bacteria (pathogens) that are often present on retail chicken products. However, with the emergence of multi-drug resistant pathogens, there are new pressures to limit the use of antimicrobial agents. This poses an additional dilemma for producers with regard to the maintenance of healthy flocks as well as preventing the presence of pathogens on retail meat. There are many aspects to consider in eliminating or minimizing pathogens in the poultry house environment. In general, pathogens cannot be eliminated unless all reservoirs that harbor these agents are also eliminated. Insects that can carry bacteria are particularly troublesome. An additional factor is that bacteria can pass antibiotic resistance genes to other bacteria. This study investigated whether bacteria fed to poultry litter beetles could transfer antibiotic resistance genes to other bacteria. The final results of this study showed that antibiotic resistance gene transfer occurred at a high level between Salmonella and E. coli in the gut of the litter beetles.

Technical Abstract: The objective of this study was to determine if conjugative transfer of antimicrobial resistance plasmids could occur within the gastrointestinal tract of lesser mealworm beetles, a common pest in poultry production facilities. In three replicate studies (n=40), beetles were exposed for 2 h to a multi-drug resistant Salmonella enterica serotype Newport strain (SN11) at 1.0×10**8 cfu/ml, followed by an 18 h exposure to nalidixic acid and rifampicin resistant E. coli JM109 at 9.0×10**6 cfu/ml. In vitro filter conjugations were performed simultaneously with beetle conjugations. Following bacterial exposure, beetles were surface disinfected, homogenized, and selectively plated for transconjugants. Transconjugants were produced in all beetles exposed to both donor and recipient bacteria. Ninety-five percent of the beetle and 100% of the in vitro filter transconjugants tested were positive for the N plasmid replicon. The A/C replicon which was also detected in the SN11 donor strain did not transfer in any of the conjugation studies. The average conjugation frequency in the beetle gut was 3.25×10**-2. These results were consistent with the filter conjugation studies that had a conjugation frequency of 3.02 ×10**-2. This study demonstrates that horizontal transfer of antimicrobial resistance plasmids can occur between Salmonella and E. coli within the gut of beetles.