Escherichia coli in urban marine sediments: interpreting virulence, biofilm formation, halotolerance, and antibiotic resistance to infer contamination or naturalization

Antimicrobial resistance and genetic diversity of Escherichia coli isolated from marine bivalves

Escherichia coli can contaminate the marine environment through sewage and accumulate in bivalve molluscs. We assessed antimicrobial resistance (AMR) mechanisms and genetic diversity of 69 E. coli isolates recovered from in natura, boiled, and purchased Perna perna mussels in Niterói city, Brazil. All isolates were sensitive to cefoxitin, imipenem, meropenem, and fosfomycin. In contrast, 61 (88.4%) isolates were not susceptible to streptomycin. We found ten (14.5%) multidrug-resistant (MDR) isolates. Extended-spectrum beta-lactamase (ESBL) production was detected in 30 (43.5%) isolates, with 14 (46.7%) isolates carrying ESBL genes (blaTEM, blaCTX-M9, blaSHV, blaCTX-M2, and blaCTX-M8/25). Quinolone/fluoroquinolone resistance was observed in 12 (17.4%) isolates, with qnrS and qnrB genes identified. Nine (13%) isolates were resistant to folate pathway inhibitors, with sul1 and sul2 genes identified. Only one (1.5%) isolate had the intI integrase gene. Most isolates had the A/C replicon (73.9%) and belonged to phylogenetic group B1 (50.7%). PFGE analysis revealed the existence of 54 genotypes, with four clusters containing isolates from different sources. The presence of ESBL-producing strains, AMR genes, and diverse plasmid replicons highlights the role of marine environments in AMR dissemination. Continuous AMR surveillance in marine ecosystems is crucial to mitigate public health risks linked to seafood consumption.

Microbial Contamination in Urban Marine Sediments: Source Identification Using Microbial Community Analysis and Fecal Indicator Bacteria

We investigated the presence of the fecal indicator bacteria Escherichia coli, and other taxa associated with sewage communities in coastal sediments, near beaches with reported poor bathing water quality, focusing on the influence of effluent from a local wastewater treatment plant (WWTP) and combined sewer overflows (CSO). Using a three-year dataset, we found that treated wastewater effluent is a significant source of sewage-associated taxa and viable E. coli in the sediments and that no seasonal differences were observed between spring and summer samples. CSO events have a local and temporary effect on the microbial community of sediments, distinct from that of treated wastewater effluent. Sediments affected by CSO had higher abundances of families Lachnospiraceae, Ruminococcaceae, and Bacteroidaceae. Sewage releases may also impact the natural community of the sediments, as higher abundances of marine sulfur-cycling bacteria were noticed in locations where sewage taxa were also abundant. Microbial contamination at locations distant from known CSO and treatment plant outlets suggests additional sources, such as stormwater. This study highlights that while coastal sediments can be a reservoir of E. coli and contain sewage-associated taxa, their distribution and potential origins are complex and are likely not linked to a single source.