Conjugative transmission of antibiotic-resistance from stream water as related to number of sulfamethoxazole but not class 1 and 2 integrase genes.

A conjugation assay was used to determine the effects of phenotypic resistance to one to up to 5 antibiotics, sampling site of origin, presence or absence of class 1 and/or class 2 integrase () genes ( and ), and the number of sulfamethoxazole resistance () and trimethoprim resistance () genes on the transfer frequencies of plasmids from environmental, antibiotic-resistant . Of 51 sulfamethoxazole and trimethoprim-resistant isolates conferring at least one gene ( , or ), 38 produced transconjugants with an overall mean frequency of 1.60 × 10 transconjugants/ donors (T/D) or 5.89 × 10 transconjugants/recipients (T/R). The presence or absence of and and the presence or absence of different targeted genes (, and/or ) were not statistically related to plasmid transfer frequencies as determined by ANOVA ( ≥ 0.05). However, isolates recovered 2 km downstream of wastewater treatment plant effluent input, and those possessing resistance to 3 antibiotics had significantly greater plasmid transfer frequency than their counterparts when calculated as T/D (ANOVA followed by Fisher's least significant difference means comparison, < 0.05). Greater plasmid transfer frequency calculated as T/D was also measured for possessing 3 compared to a single gene. The in-vitro frequency suggests that horizontal gene transfer of conjugative mediated-antibiotic () resistance genes may be significant among resistant, stream bacteria.