Enteric bacteria from a One Health perspective: fecal indicators and antibiotic resistance

The rise of antibiotic-resistant enteric bacteria poses a significant threat to global health, highlighting the need for a One Health approach. Enteric bacteria such as Enterococcus faecalis (E. faecalis), Enterococcus faecium (E. faecium), and Escherichia coli (E. coli) are key indicators of water quality and environmental risk to public health. Their pathogenicity and ability to acquire antibiotic-resistant genes (ARGs) through horizontal gene transfer (HGT) exacerbate the issue. Extended-spectrum β-lactamase-producing E. coli (ESBL-Ec) and vancomycin-resistant enterococci (VRE) are serious human and animal pathogens present in the environment, potentially transmitted between animals and humans. Paper I addresses the distribution of fecal indicator bacteria, specifically E. faecalis, E. faecium, and E. coli, including their multidrug resistance (MDR) levels in the Örebro River, Sweden, from 2010 to 2011. The results revealed that VRE and ESBL-Ec strains were detected, highlighting the spread of significant antibiotic-resistant bacteria in relatively unpolluted regions. Paper II investigated third-generation cephalosporin-resistant E. coli (3GCR-Ec) strains in 2023 in Fyrisån river, Uppsala, Sweden. Results showed significantly higher concentrations of 3GCR-Ec, including ESBL-Ec, at the Wastewater treatment plant (WWTP) compared to Lake Mälaren. Multi-locus-sequence types (MLSTs) associated with virulence and MDR ST69, ST10, ST1193, and ST1722 were reported at multiple sampling points, while ST131 was found only downstream of the WWTP in March and November. ARGs were detected in all isolates. Notably, 65% of isolates carried an ESBL gene, and 43% harbored blaCTX-M-15, which is commonly associated with clinically relevant strains, indicating an urgent need to mitigate the spread of these pathogenic bacteria. Paper III, an in-silico analysis of Extended-spectrum cephalosporin-resistant E. coli (ESC-Ec) (collected in May 2011), was performed to examine the interconnectedness between humans and livestock in rural Cambodia. Evidence of both clonal transmission and HGT was observed. Twenty-three percent of isolates were similar strains clustering into ten core genome MLST, circulating among the sources and across households and villages. IncF plasmids were identified in 75.9% of isolates, likely facilitating ARG transmission across hosts. In conclusion, the findings of this thesis underscore the critical need for enhanced surveillance and interventions to mitigate the spread of antimicrobial resistance, particularly in low-income settings.