High Diversity of Extended-Spectrum Beta-Lactamase-Producing Bacteria in an Urban River Sediment Habitat

Abstract

Antibiotic-resistant bacteria (ARB) have been surveyed widely in water bodies, but few studies have determined the diversity of ARB in sediment, which is the most taxon-abundant habitat in aquatic environments. We isolated 56 extended-spectrum β-lactamase (ESBL)-producing bacteria from a single sediment sample taken from an urban river in China. All strains were confirmed for ESBL-producing capability by both the clavulanic acid combination disc method and MIC determination. Of the isolated strains, 39 were classified as Enterobacteriaceae (consisting of the genera Escherichia , Klebsiella , Serratia , and Aeromonas ) by 16S rRNA gene sequencing and biochemical analysis. The present study identifies, for the first time, ESBL-producing strains from the families Brucellaceae and Moraxellaceae . The bla _CTX-M gene was the most dominant of the ESBL genes (45 strains), while the bla _TEM gene was the second-most dominant (22 strains). A total of five types of bla _CTX-M fragments were identified, with both known and novel sequences. A library of bla _CTX-M cloned from the sediment DNA showed an even higher diversity of bla _CTX-M sequences. The discovery of highly diverse ESBL-producing bacteria and ESBL genes, particularly bla _CTX , in urban river sediment raises alarms for potential dissemination of ARB in communities through river environments.