Citrobacter spp. and Enterobacter spp. as reservoirs of carbapenemase blaNDM and blaKPC resistance genes in hospital wastewater.

Antibiotic resistance has emerged as a global threat to public health, generating a growing interest in investigating the presence of antibiotic-resistant bacteria in environments influenced by anthropogenic activities. Wastewater treatment plants in hospital serve as significant reservoirs of antimicrobial-resistant bacteria, where a favorable environment is established, promoting the proliferation and transfer of resistance genes among different bacterial species. In our study, we isolated a total of 243 strains from 5 hospital wastewater sites in Mexico, belonging to 21 distinct Gram-negative bacterial species. The presence of β-lactamase was detected in 46.9% (114/243) of the isolates, which belonging to the Enterobacteriaceae family. We identified a total of 169 β-lactamase genes; bla_TEM in 33.1%, bla_CTX-M in 25.4%, bla_KPC in 25.4%, bla_NDM 8.8%, bla_SHV in 5.3%, and bla_OXA-48 in 1.1% distributed in 12 different bacteria species. Among the 114 of the isolates, 50.8% were found to harbor at least one carbapenemase and were discharged into the environment. The carbapenemase bla_KPC was found in six Citrobacter spp. and E. coli, while bla_NDM was detected in two distinct Enterobacter spp. and E. coli. Notably, bla_NDM-1 was identified in a 110 Kb IncFII conjugative plasmid in E. cloacae, E. xiangfangensis, and E. coli within the same hospital wastewater. In conclusion, hospital wastewater showed the presence of Enterobacteriaceae carrying a high frequency of carbapenemase bla_KPC and bla_NDM. We propose that hospital wastewater serves as reservoirs for resistance mechanism within bacterial communities and creates an optimal environment for the exchange of this resistance mechanism among different bacterial strains.

Importance: The significance of this study lies in its findings regarding the prevalence and diversity of antibiotic-resistant bacteria and genes identified in hospital wastewater in Mexico. The research underscores the urgent need for enhanced surveillance and prevention strategies to tackle the escalating challenge of antibiotic resistance, particularly evident through the elevated frequencies of carbapenemase genes such as bla_KPC and bla_NDM within the Enterobacteriaceae family. Moreover, the identification of these resistance genes on conjugative plasmids highlights the potential for widespread transmission via horizontal gene transfer. Understanding the mechanisms of antibiotic resistance in hospital wastewater is crucial for developing targeted interventions aimed at reducing transmission, thereby safeguarding public health and preserving the efficacy of antimicrobial therapies.