Mallory Alman

Wastewater treatment plants (WWTPs) are known to frequently discharge antibiotic resistance genes (ARGs) into the environment, a practice which contributes to ARG transfer among environmental bacteria and aids the spread of antibiotic resistance. This study focused on investigating the effects of two secondary effluent treatment methods--chlorination and maturation ponds--on ARG concentrations in effluent from two WWTPs in Chennai, India. One WWTP uses chlorine disinfection and is referred to as "Plant C", while the other uses a maturation pond in place of disinfection and is designated "Plant M". Grab samples were taken at plant influent and before and after each treatment stage of the two plants. Microbial biomass from each sample was then concentrated by passage through three 0.22 micrometer filters to produce triplicate samples for DNA extraction. DNA samples from the secondary and final effluent of each plant were analyzed for concentration of genes 16S rRNA, intI1, and sul1 using quantitative polymerase chain reaction (qPCR). Wilcoxon rank-sum tests were used to determine whether intI1 and sul1 gene abundance normalized to 16S differed significantly among each plant's influent, secondary clarifier effluent, and final effluent. Chlorination at Plant C resulted in an insignificant (p>0.20) increase in sul1 and intI1 relative abundance, suggesting limited risk of selection for ARGs on the day sampled. In contrast, maturation pond treatment at Plant M significantly (p<0.001) increased sul1 relative abundance, though no effect on intI1 relative abundance was observed. The enhancement of sul1 following maturation pond treatment poses the concern that maturation ponds can select for antibiotic resistance, as few other studies have examined the impact of these ponds on ARG abundance. Further investigation is required to gain a complete understanding of each plant's effect on ARGs as well as determine what factors encourage selection for antibiotic resistance in maturation ponds.