Background/Objectives: The spread of antibiotic resistance, particularly through Enterococcus spp., in wastewater treatment plants (WWTPs) poses significant public health risks. Given that research on antibiotic-resistant enterococci and their antibiotic-resistance genes in aquatic environments is limited, we evaluated the role of Enterococcus spp. in WWTPs by comparing the antibiotic resistance rates, gene prevalence, biofilm formation, and residual antibiotics in the influent and effluent using culture-based methods. Methods: In 2022, influent and effluent samples were collected from 11 WWTPs in South Korea. Overall, 804 Enterococcus strains were isolated, and their resistance to 16 antibiotics was assessed using the microdilution method. Results: High resistance to tetracycline, ciprofloxacin, kanamycin, and erythromycin was observed. However, no significant differences in the overall resistance rates and biofilm formation were observed between the influent and effluent. Rates of resistance to ampicillin, ciprofloxacin, and gentamicin, as well as the prevalence of the tetM and qnrS genes, increased in the effluent, whereas resistance rates to chloramphenicol, florfenicol, erythromycin, and tylosin tartrate, along with the prevalence of the optrA gene, decreased. E. faecium, E. hirae, and E. faecalis were the dominant species, with E. faecalis exhibiting the highest resistance. Conclusions: Our results suggest that WWTPs do not effectively reduce the rates of resistant Enterococcus spp., indicating the need for continuous monitoring and improvement of the treatment process to mitigate the environmental release of antibiotic-resistant bacteria.

Waterborne epidemics of human hepatitis virus A and E (HAV and HEV) have been reported worldwide. Molecular biology techniques, such as reverse transcription polymerase chain reaction (RT-PCR), have been widely used to detect the two hepatitis viruses. However, comparative studies of various types of samples are needed, and different environmental factors, including the low copy pathogens, presence of PCR inhibitors in the sample, unknown non-specific reaction with template, and sequence diversity leading to new variants in viruses, should be considered. In addition, standard positive material is required to determine the accuracy of the PCR and should be able to distinguish between false and real positives. In this study, we developed RT-PCR primer sets and optimised standard templates for HAV and HEV detection to address the above concerns associated with test sensitivity and possible PCR inhibition. Finally, previously reported diagnostic methods of HAV and HEV were compared and an applicability test using groundwater was performed. The nested RT-PCR developed in this study is expected to contribute to assess water safety by monitoring HAV and HEV in non-disinfected water, like groundwater.

The increasing global incidence of quinolone antimicrobial resistance poses a considerable public health concern. The aquatic environment, particularly wastewater treatment plants (WWTPs), serves as a major reservoir for antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), leading to the dissemination of antibiotic resistance. This study aimed to assess the prevalence and factors contributing to quinolone antibiotic resistance in Escherichia coli isolates obtained from effluents of 33 WWTPs. A total of 1082 E. coli isolates were analyzed, 32.6% and 17.1% of which showed resistance to nalidixic acid and ciprofloxacin, respectively. Phenotypic and genotypic analyses of antibiotic resistance demonstrated that quinolone resistance primarily originated from chromosomal mutations in the gyrA, parC, and parE genes, known as quinolone resistance-determining regions (QRDRs). The amino acid substitution at codon 83 in gyrA was closely associated with nalidixic acid resistance, whereas substitutions at codon 87 in gyrA and codon 80 in parC were significantly associated with ciprofloxacin resistance. The plasmid-mediated quinolone resistance (PMQR) genes qnrS and qnrB were identified in 41 isolates (11.5%) and 15 isolates (4.2%), respectively. Thus, we confirmed that the quinolone resistance in E. coli in WWTPs primarily occurs through QRDR mutations rather than through the acquisition of PMQR genes. Phylogenetic analysis revealed that most quinolone-resistant isolates belonged to the B1, A, B2, and D phylogenetic groups. Notably, the B2 group, which is responsible for extraintestinal infections, exhibited the highest rate of quinolone resistance. These findings provide novel insights into the presence and mechanisms of quinolone resistance in E. coli isolates from WWTPs, emphasizing the need for further research and understanding of quinolone resistance in the environment.

Groundwater is an essential drinking water source for humans. However, improper groundwater management leads to fecal contamination and waterborne diseases caused by viral pathogens. Therefore, this study aimed to investigate norovirus (NoV) contamination by conducting nationwide monitoring over five years (2019–2023). Groundwater samples were analyzed for water quality parameters, indicator microorganisms, NoV prevalence, and viral genotypes. Water quality was assessed for temperature, turbidity, and residual chlorine, whereas microorganisms were analyzed for total coliforms, Escherichia coli, and NoV genotypes. Of the 600 sites, 11 (1.8%) were NoV-positive, irrespective of season or location. Low residual chlorine levels (0.02–0.75 mg/L) were observed, possibly limiting viral inactivation. Total coliforms were detected in only three NoV-positive samples, and E. coli was absent. NoV genotypes were identified as GI.1 and GII.4, with GII.4 being the most frequently detected genotype. The present study demonstrated that periodic monitoring and expanded nationwide efforts are required for effective groundwater management and public health protection.