Indirect Evidence of Transposon-Mediated Selection of Antibiotic Resistance Genes in Aquatic Systems at Low-Level Oxytetracycline Exposures

Abstract

Subinhibitory levels of antibiotics can promote the development of antibiotic resistance in bacteria. However, it is unclear whether antibiotic concentrations released into aquatic systems exert adequate pressure to select populations with resistance traits. To examine this issue, 15 mesocosms containing pristine surface water were treated with oxytetracycline (OTC) for 56 days at five levels (0, 5, 20, 50, and 250 microg L(-1)), and six tetracycline-resistance genes (tet(B), tet(L), tet(M), ted(O), tet(Q), and tet(W)), the sum of those genes (tet(R)), "total" 16S-rRNA genes, and transposons (Tn916 and Tn 1545) were monitored using real-time PCR. Absolute water-column resistance-gene abundances did not change at any OTC exposure. However, an increase was observed in the ratio of tet(R) to 16S-rRNA genes in the 250 microg L(-1) OTC units, and an increase in the selection rate of Tc(r) genes (relative to 16S-rRNA genes) was seen when OTC levels were at 20 microg L(-1). Furthermore, tet(M) and Tn916/1545 gene abundances correlated among all treatments (r2 = 0.701, p = 0.05), and there were similar selection patterns of tetR and Tn916/1545 genes relative to the OTC level, suggesting a possible mechanism for retention of specific resistance genes within the systems.

Impact of reclaimed water irrigation on antibiotic resistance in public parks, Beijing, China

“…However, a previous study demonstrated that low concentrations of antibiotics could also induce ARGs and/ or stimulates horizontal gene transfer of ARGs (Storteboom et al, 2010). Subinhibitory concentrations of oxytetracycline as low as 20 mg L À1 were able to select for tetracycline resistance, as shown by an increasing ratio of tet over 16S rRNA gene in surface water mesocosms (Knapp et al, 2008). It was found that the patterns of antibiotics distribution among different parks were different, including parks using reclaimed water from the same WWTPs (Table S1 and Fig.…”

Real-time PCR methods for quantitative monitoring of streptomycin and tetracycline resistance genes in agricultural ecosystems

“…Singleplex qPCR using SYBR green detection has previously been used to detect certain antibiotic resistance genes in environmental samples, most frequently identified in water or waste water samples (Volkmann et al, 2004(Volkmann et al, , 2007Borjesson et al, 2009;Knapp et al, 2008;Koike et al, 2007;Pruden et al, 2006;Smith et al, 2004). The SYBR Green RT-PCR chemistry may generate false positive results as it binds to any double-stranded DNA, and as such can also bind to non-specific double-stranded DNA sequences.…”

Antibiotic residues and resistance in the environment

“…For sulfadiazine, concentrations of 150 µg kg -1 in soil were shown to have a selective effect on the resistant population . Increased selection for tetracycline resistant genes was also apparent at exposures as low as 20 μg L -1 OTC in surface water mesocosms (Knapp, 2008). Interestingly, a recent study suggests that the manure itself could be contributing to resistance, apparently by selectively supporting the growth of beta lactam resistant bacteria, although the exact mechanism is unknown (Udikovic-Kolica, 2014).…”