Detection of antimicrobial resistance in Escherichia coli and Salmonella spp. Originated from cultivated oysters and estuarine waters

Abstract

The raising and spreading antimicrobial resistance (AMR) bacteria in humans, animals, and environment is a serious global public health issue. Improper use of antimicrobial agents can promote resistant bacteria, and as a result, they can circulate in the environment. Contamination of AMR in the environment can increase the risk of AMR distribution in humans, animals, and the environment. Monitoring and surveillance of AMR in the environmental sector are limited compared to animal and human sectors. The objectives of this study were to determine phenotype and genotype of AMR and extended-spectrum beta-lactamase (ESBL) production in Escherichia coli and Salmonella isolated from cultivated oysters and estuarine waters, to examine serovars of Salmonella isolates, and to detect virulence genes in E. coli and Salmonella isolated from cultivated oysters (n=144) and estuarine water (n=96). E. coli (n=409) and Salmonella (n=126) isolates were obtained from cultivated oysters and estuarine waters from Phang Nga, Thailand. The predominant serovars of Salmonella were Paratyphi B (13.50%), followed by Eastbourne (12.70%), and II (15.87%). The resistance to at least one antimicrobial agent was found in E. coli (94.13%) and Salmonella (96.82%). The multidrug resistance E. coli (42.60%) and Salmonella (23.02%) were observed. The blaTEM (31.55%), tet(A) (25.44%), and strA (14.92%) were the most prevalent resistance genes found in E. coli isolates, while sul3 (14.29%), blaTEM (11.91%), and cmlA (11.91%) were commonly found in resistance Salmonella. Phenotypic ESBL production was detected in eight E. coli isolates from estuarine waters, and two Salmonella isolates from oysters. One of E. coli and Salmonella isolates that harbored blaTEM-1 corresponded to broad-spectrum beta-lactamase. However, four E. coli isolates harbored blaCTX-M genes. The most common virulence genes of E. coli isolates were istx1 (17.85%) and lt (11.74%). For Salmonella isolates, high prevalence of invA (76.98%), stn (76.98%), and fimA (69.05%) were observed. The E. coli isolates that resistant to ampicillin were resistant to chloramphenicol and trimethoprim (p<0.0001). Furthermore, the E. coli isolates harboring stx1 and stx2 were more likely to resistant to chloramphenicol than those did not contain virulence genes (p<0.0001). The Salmonella isolates that consisted of invA and fimA were more likely to be resistant to various antibiotics, including ampicillin, chloramphenicol, tetracycline, and trimethoprim. In conclusion, oysters and estuarine water are one of the potential AMR hotspots in the environment. Therefore, continuing monitoring and surveillance of AMR should be implemented in the environment.