Submitted to: Risk Assessment Conference Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 10/5/2004
Publication Date: 12/5/2004
Citation: Jackson, C.R. 2004. Risk of antibiotic transfer among various gut microorganisms. Risk Assessment Conference Proceedings. Abstract. M14.2. 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, antimicrobial resistance gene transfer from normal flora bacteria to other microflora, including transient colonizers, is possible. Close proximity, solid surfaces, and high numbers are conducive for transfer of genes via conjugation, the most common mechanism of gene transfer. However, transfer of genes via transformation or transduction is also possible and probable. Genes likely transfer between disparate bacteria while encoded in plasmids, transposons, conjugal transposons, and integrons. Both indirect and direct evidence exists regarding the ability of normal and transient intestinal microflora to transfer antimicrobial resistance determinants to other bacteria within the intestine or 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 populations of normal flora from the mouth, vagina, and intestinal tract as well as in a pathogenic strain of Neisseria. Direct evidence has been recognized through 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 discussed as we explore the role of normal flora in the dissemination and persistence of antimicrobial resistance.