We tested 34 American Type Culture Collection (ATCC) and 168 clinical bacterial isolates, from the human urogenital and oral tracts and streptococci isolated from cows with mastitis, for the presence of the tetQ gene using a polymerase chain reaction (PCR) assay and DNA-DNA hybridization. The identities of PCR products were confirmed by Southern blot hybridization of whole-cell DNA. Eleven of the ATCC strains were positive for tetQ, including five Bacteroides spp., five Prevotella spp. and a single isolate of Mitsuokella multiacidus. Twenty-eight (29%) of the 95 clinical Gram-negative isolates carried the tetQ gene, while eight (11%) of the 73 clinical Gram-positive isolates carried the tetQ gene. This is the first description of tetQ in Gram-positive species. All isolates except one Peptostreptococcus sp. carried tetQ integrated into the chromosome. The tetQ gene could be transferred from Prevotella bivia, Bacteroides ovatus, Bacteroides fragilis, Bacteroides vulgatus and Bacteroides distasonis into an Enterococcus faecalis recipient at frequencies of 10(-7)-10(-9) per recipient. In contrast, tetQ failed to transfer from two isolates of Prevotella intermedia, two isolates of Porphyromonas gingivalis, one isolate of Mobiluncus curtisii and one isolate of Peptostreptococcus sp. The latter two are Gram-positive species. The PCR assay was used to screen 198 proteinase K-treated biopsies of prostate, periprostate and bladder from 84 men with prostatitis. Thirty-four (40%) of the patients had one or more positive samples, suggesting that the PCR assay could be of value in screening patient material directly for the presence of bacteria.