Bathing in resistance: evidence of multidrug-resistant bacteria in recreational coastal waters in Niterói City, Rio de Janeiro, Brazil

Introduction Antibiotic resistance is a critical One Health issue, necessitating continuous investigation of bacterial diversity and resistance, particularly in non-clinical environments. This study investigated the presence of antimicrobial-resistant bacteria in waters collected from four sampling points of a recreational beach in the city of Niterói, Rio de Janeiro state. Methodology Water samples were collected from four points along the beach, and after serial dilutions, the samples were plated onto selective media for bacterial isolation. Bacterial identification was performed using matrix-assisted laser desorption ionization–time-of-flight (MALDI–TOF) mass spectrometry. Antimicrobial susceptibility was assessed using the disk diffusion method and interpreted according to Clinical & Laboratory Standards Institute (CLSI) standards. DNA from Gram-negative bacteria with detected phenotypic resistance was extracted, and PCR was used to investigate the presence of β-lactamase resistance genes. The bla GES gene was sequenced and deposited in GenBank. The multiple antibiotic resistance phenotype (MARP) and multiple antibiotic resistance index (MARI) were calculated based on the number of antibiotics each isolate was resistant to. Results The presence of the genes bla GES , bla SHV , bla TEM , and bla CTX-M , which confer resistance to clinically relevant β-lactams, was detected in four members of the order Enterobacterales. A bla GESS determinant was detected in an isolate of Citrobacter freundii in combination with phenotypic resistance to ciprofloxacin, erythromycin, sulfamethoxazole/trimethoprim, and tetracycline, characterizing a multidrug-resistant phenotype. This observation, when combined with findings from previous surveys of Guanabara Bay, indicated that the bla GES determinants are either established or continually introduced into this important ecosystem. The multiple antibiotic resistance indices ranged from 0.19 to 0.62, with a strain of Klebsiella variicola showing the highest value, based on resistance to 11 of the 16 antimicrobials examined. Discussion The data presented herein demonstrated the presence of an abundant diversity of antimicrobial-resistant bacteria in waters used for bathing, sailing, and fishing by a large population of humans and emphasizes the requirement for enhanced monitoring of recreational waters along the Guanabara Bay coastline.