Antimicrobial resistance (AMR) is one of the major public health challenges of the 21st century. In this context, hospital effluents are relevant sources of dissemination of antimicrobials, resistance genes, and multidrug-resistant bacteria into aquatic ecosystems. Understanding the contribution of these effluents as sources of selective pressure and resistance spread is essential from a One Health perspective. This study aimed to assess the presence of antimicrobials and resistant bacteria in hospital effluent.

Hospital effluent samples were collected in May 2025 in the municipality of Lapa, Paraná. Analyses were conducted for antimicrobials of the β-lactam and tetracycline classes, along with bacterial susceptibility testing by antibiogram. Antimicrobial quantification was performed using the TwinSensor test. To detect β-lactam-resistant bacteria, serial dilutions were plated (200 µL of the 10⁻⁵ dilution) on ESBL medium. Colonies with the highest concentrations were isolated and inoculated into Mueller-Hinton medium for susceptibility testing to ciprofloxacin (CIP), tetracycline (TET), amoxicillin + clavulanate (AMC), azithromycin (AZI), and penicillin (PEN). All analyses were performed in triplicate.

β-lactam-resistant strains were identified, including Klebsiella pneumoniae, Escherichia coli, Proteus spp., and Pseudomonas spp. The following antimicrobials were detected: tetracycline (76.66 ± 5.77 µg/L), oxytetracycline (56.66 ± 5.73 µg/L), amoxicillin (1.83 ± 0.28 µg/L), and penicillin (2.66 ± 0.57 µg/L). The antibiogram revealed K. pneumoniaestrains resistant to PEN, CIP, AMC, and TET, as well as E. coli strains resistant to PEN and AZI. The hospital primarily treats patients with respiratory diseases such as pneumonia, which may explain the presence of resistant K. pneumoniae—a pathogen commonly associated with this clinical condition.

The analyzed hospital effluent demonstrated a potential One Health risk, contributing to the environmental dissemination of antimicrobials and resistant bacterial strains. These findings reinforce the need for continuous monitoring and improvement of effluent treatment processes, with an emphasis on mitigating the spread of antimicrobial resistance.