EVIDENCE FOR NATURAL HORIZONTAL TRANSFER OF TETQ BETWEEN BACTERIA THAT NORMALLY COLONIZE HUMANS AND BACTERIA THAT NORMALLY COLONIZE LIVESTOCK

Though numerous studies have shown that gene transfer occurs between d istantly related bacterial genera under laboratory conditions, the fre quency and breadth of horizontal transfer events in nature remain unkn own. Previous evidence for natural intergeneric transfers came from st udies of genes in human pathogens, bacteria that colonize the same hos t. We present evidence that natural transfer of a tetracycline resista nce gene, fete, has occurred between bacterial genera that normally co lonize different hosts. A DNA sequence comparative approach was taken to examine the extent of horizontal fete dissemination between species of Bacteroides, the predominant genus of the human colonic microflora , and between species of Bacteroides and of the distantly related genu s Prevotella, a predominant genus of the microflora of the rumens and intestinal tracts of farm animals. Virtually identical fete sequences were found in a number of isolate pairs differing in taxonomy and geog raphic origin, indicating that extensive natural gene transmission has occurred. Among the exchange events indicated by the evidence was the very recent transfer of an allele of fete usually found in Prevotella spp. to a Bacteroides fragilis strain.