Metagenomic analysis reveals the influence of wastewater discharge on the microbial community structures and spread of antibiotic-resistant bacteria at Mohar river, Gujarat.

An extensive use of antibiotics has evolved bacterial antimicrobial resistance (AMR) and its spread through horizontal gene transfer within microbial communities of the natural environment. The water bodies receiving wastewater from sewage treatment plant (STP) serve as a conducive reservoir for the spread of antibiotic-resistant bacteria (ARB). This study revealed occurrence of multidrug-resistant and extended spectrum β-lactamase (ESBL) producing bacteria present in STP inlet (SI1), outlet (SO1), riverine environment receiving the STP wastewater (MP1), and control site (C1) of the river Mohar, Gujarat. Microbial community analysis revealed Proteobacteria and Firmicutes as dominating phyla in water samples of Mohar River sites. Shotgun analysis showed presence of antibiotic-degrading enzymes and pathways. The resistance profiling of ARBs showed the higher resistance towards cefotaxime at MP1 (77.4%), followed by SO1 (70.5%), SI1 (64.14%), and the least at C1 (57.13%). The highest ESBL isolates were observed at MP1 (96.42%), followed by SI1 (84.51%), SO1 (80.55%), and C1 (78.57%). Moreover, the RT-qPCR analysis for abundance of intI1 gene (responsible for HGT) showed a descending pattern from SI1 to the C1. The abundance of intI1 was found to correlate positively with mercury, chromium, and chlorine, and a negative correlation was observed with arsenic. The results obtained in this research suggest that AMR spreads and evolves in the water environment via discharge of wastewaters from STPs into the river ecosystems.