Quantifying Nonspecific TEM β-Lactamase ( bla TEM ) Genes in a Wastewater Stream

Abstract

To control the antibiotic resistance epidemic, it is necessary to understand the distribution of genetic material encoding antibiotic resistance in the environment and how anthropogenic inputs, such as wastewater, affect this distribution. Approximately two-thirds of antibiotics administered to humans are β-lactams, for which the predominant bacterial resistance mechanism is hydrolysis by β-lactamases. Of the β-lactamases, the TEM family is of overriding significance with regard to diversity, prevalence, and distribution. This paper describes the design of DNA probes universal for all known TEM β-lactamase genes and the application of a quantitative PCR assay (also known as Taqman) to quantify these genes in environmental samples. The primer set was used to study whether sewage, both treated and untreated, contributes to the spread of these genes in receiving waters. It was found that while modern sewage treatment technologies reduce the concentrations of these antibiotic resistance genes, the ratio of bla TEM genes to 16S rRNA genes increases with treatment, suggesting that bacteria harboring bla TEM are more likely to survive the treatment process. Thus, β-lactamase genes are being introduced into the environment in significantly higher concentrations than occur naturally, creating reservoirs of increased resistance potential.