Sequence type ST131 and ST10 complex (ST617) predominant among CTX-M-15-producing Escherichia coli isolates from Nigeria.

Of 109 clinical Escherichia coli isolates from two major tertiary hospitals in Lagos (University Teaching Hospital and the National Orthopaedic Hospital Igbobi), 14 (12.8%) extended-spectrum beta-lactamse (ESBL) producers were characterized using PCR and sequencing, ERIC-PCR and multilocus sequence typing. All ESBL-producing isolates encoded only the CTX-M-15 gene. Clonal group ST131 (35.7%) was the predominant ST, followed by ST617 (28.6%). Isolated cases of other sequence types were also observed. Plasmid-mediated quinolone resistance genes qnrA, qnrB1 and aac-(6')-lb-cr were detected among these ESBL isolates of different clonal groups. This is the first description of the clonality of CTX-M-15-producing E. coli from Nigeria. The presence of diverse clonal lineages shows the continuing potential for genetic diversification and emergence of new epidemic strains.