Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2003
Publication Date: 7/1/2004
Citation: Hume, M.E., Poole, T.L., Pultz, N.J., Hanrahan, J.A., Donskey, C.J. 2004. Inhibition of vancomycin-resistant enterococcus by continuous-flow cultures of human stool microflora with and without anaerobic gas supplementation. Current Microbiology. 48:364-367. Interpretive Summary: Human stool bacteria were used to examine whether growing the bacteria in a gas environment free of oxygen is necessary for the bacteria to maintain their ability to inhibit the growth of the human intestinal pathogen vancomycin-resistant Enterococcus faecium (VRE). Human stool bacteria were grown under a continuous supply of nitrogen gas, with no supply of gas, or with continuous supply of room air. Supplying the bacteria with either no gas or with nitrogen gas supported the growth of bacteria that grow only when oxygen is not present and supported the growth inhibition and elimination by these bacteria of VRE added to the container. Supplying the bacteria with room air resulted in a decrease in the numbers of bacteria that only grow when oxygen is not present and resulted in VRE not being eliminated when added to the container. The ability of the bacteria to eliminate VRE when gas was not supplied is likely the result of oxygen-using bacteria present in the stool rapidly using any harmful oxygen that may enter the system. The conclusion is that supplying the human stool bacteria with nitrogen gas is not necessary for maintenance of the ability to eliminate VRE. The results indicate a more cost-effective method for the maintenance of these human stool bacteria that competitively exclude VRE.
Technical Abstract: Aims: An in vitro continuous-flow competitive exclusion (CFCE) culture model of human stool microflora was used to examine whether supplemental anaerobic gas is necessary for maintenance of anaerobes and inhibition of vancomycin-resistant Enterococcus (VRE). Methods and Results: CFCE cultures of human stool microflora were maintained with supplemental nitrogen, without supplemental nitrogen, or with percolated room air. Cultures with or without supplemental nitrogen maintained >9 log10 CFU ml-1 of obligate anaerobes and eliminated 106 CFU ml-1 of VRE. When room air was percolated into the culture, anaerobes were detected at <2 log10 CFU ml-1 and the same VRE inoculum was not eliminated (P < 0.001). Conclusions: Supplemental nitrogen gas was not necessary for maintenance of anaerobes or inhibition of VRE. Significance and Impact of the Study: These data suggest that anaerobic gas is not necessary for in vitro efficacy of CFCE cultures of human stool microflora, and that obligate anaerobes are the component of the intestinal microflora that inhibit VRE.