# Silent Waterborne Carriers of Carbapenem-Resistant Gram-Negative Bacilli and Antimicrobial Resistance Genes in Rio de Janeiro’s Aquatic Ecosystems

## TL;DR

This study found antibiotic-resistant bacteria and resistance genes in polluted water bodies in Rio de Janeiro, linking water contamination to public health risks.

## Contribution

The study identifies carbapenem-resistant Gram-negative bacteria and resistance genes in recreational waters exposed to human effluents.

## Key findings

- Carbapenem-resistant isolates accounted for 49.4% of total isolates, with blaKPC, blaTEM, blaVIM, and blaSPM genes detected.
- A Citrobacter braakii isolate showed resistance to all tested antimicrobials, indicating untreatable infection risks.
- The intl1 gene was found in 10% of isolates, suggesting potential horizontal gene transfer.

## Abstract

Background/Objectives: Water pollution caused by human activities disrupts ecosystems and promotes the spread of antimicrobial resistance genes (ARGs), posing a public health threat. This study investigated the presence of resistant Gram-negative bacteria and resistance genes in water from two sites occasionally exposed to domestic and hospital effluents, the Carioca River (CR) and Rodrigo de Freitas Lagoon (RFL), both used for recreation. Methods: Physicochemical parameters and coliform levels were measured. Bacterial isolates were identified by Matrix-Assisted Laser Desorption Ionization–Time-of-Flight Mass Spectrometry (MALDI-TOF MS) and tested for antimicrobial susceptibility using disk diffusion. The Minimum Inhibitory Concentration (MIC) was determined using the E-test® and broth microdilution methods. PCR was used to detect carbapenem resistance and other ARGs from the DNA of bacterial isolates obtained from water samples. Results: CR presented signs of environmental degradation, with low dissolved oxygen and high coliform counts. One Citrobacter braakii isolate showed resistance to all tested antimicrobials, raising concern for untreatable infections. Carbapenem-resistant isolates accounted for 49.4% of the total, harboring blaKPC (20%), blaTEM (5%), blaVIM (5%), and blaSPM (5%). The intl1 gene was found in 10% of isolates, indicating potential horizontal gene transfer. Conclusions: The findings from a one-day sampling reveal the presence of multidrug-resistant bacteria that carry antimicrobial resistance genes in polluted aquatic systems. These highlight the connection between water contamination and antimicrobial resistance. The evidence underscores the urgent need for environmental monitoring and effective management strategies to reduce public health risks.