| Summary: | Bivalves are filter-feeding organisms and biomarkers of bacterial pollution. Our study aimed to analyze the occurrence and characteristics of extended-spectrum β-lactamase (ESBL)- and carbapenemase-producing <i>Escherichia coli</i> among bivalves. A total of 522 bivalve samples were collected along Portuguese shellfish production areas. Homogenized samples were screened for <i>E. coli</i> contamination on corresponding selective plates, allowing for concomitant growth of <i>Klebsiella pneumoniae</i>. <i>E. coli</i> growth was observed in 39% of the samples. Subsequent selective screening identified nine samples (4.4%) contaminated with ESBL producers, corresponding to <i>E. coli</i> (<i>n</i> = 7) and <i>K. pneumoniae</i> (<i>n</i> = 2), while a single carbapenemase-producing <i>K. pneumoniae</i> (0.5%) was identified. ESBLs were all CTX-M-types commonly identified in human isolates, i.e., CTX-M-32 (<i>n</i> = 4), CTX-M-15 (<i>n</i> = 4), and CTX-M-14 (<i>n</i> = 1). The carbapenemase producer harbored the <i>bla</i><sub>GES-5</sub> gene located on a ColE plasmid. Clonality was evaluated by multilocus sequence typing, identifying <i>E. coli</i> backgrounds as ST10, ST23, ST540, ST617, ST746, SLV206, and SLV2325, commonly identified among environmental and human strains. The <i>K. pneumoniae</i> isolates belonged to ST834, ST15, and DLV644. The occurrence of ESBL- and carbapenemase-producing Enterobacteriaceae in bivalves reveals how the marine environment constitutes a reservoir of critical bacterial pathogens, thus potentially representing a risk to human health.
|
|---|