Genetic Resistance-ease of acquisition and role of commensals

Authors: Frye, Jonathan; Jackson, Charlene; Cray, Paula

Submitted to: USDA Annual Food Safety Research Planning Meeting
Publication Type: Proceedings
Publication Acceptance Date: 2/22/2007
Publication Date: 2/22/2007
Citation: Frye, J.G., Jackson, C.R., Cray, P.J. 2007. Genetic Resistance-ease of acquisition and role of commensals. USDA Annual Food Safety Research Planning Meeting. February 21-23,2007. Shepherdstown, West Virginia.

Interpretive Summary:

Technical Abstract: The majority of the normal intestinal microflora is composed of anaerobic Gram-positive and Gram-negative bacteria such as Bifidobacterium, Eubacterium, and Bacteroides. Other minor inhabitants consist of facultative Gram-negative and Gram-positive bacteria including Escherichia coli and Enterococcus, respectively, as well as important opportunistic pathogens such as Clostridium. Because of the diversity of flora in the intestine and the high number of bacteria residing in the colon, the risk of antimicrobial resistance gene transfer from normal flora bacteria to other microflora and to transient colonizers is possible. Close proximity, solid surfaces, and high numbers are conducive for transfer mechanisms such as conjugation, and although many of the events of antimicrobial transfer are probably due to conjugation, transfer via transformation and transduction are also possible and probable. Plasmids, transposons, conjugal transposons, and integrons have all been shown to transfer between disparate bacteria. Both indirect and direct evidence exists on the ability of normal intestinal microflora as well as other microflora to transfer antimicrobial resistance determinants to other inhabitants of the intestine and to transient colonizers. One of the most conclusive lines of indirect evidence can be found in the example of tetM. tetM has been detected in diverse normal flora bacteria from the mouth, vagina, and intestinal tract as well as in a pathogenic strain of Neisseria. Direct evidence of transfer of resistance has been found in the transfer of broad host range plasmid pAM'1 from Enterococcus faecium to Lactobacillus reuteri in the intestinal tract of Lactobacillus-free infant mice. Mechanisms of antimicrobial resistance, factors affecting transfer in the intestinal tract, and published studies on risk assessment data will be further discussed in order to elucidate the role of normal flora in dissemination and persistence of antimicrobial resistance.