Changing prevalence of Escherichia coli with CTX-M–type extended-spectrum β-lactamases in outpatient urinary E. coli between 2003 and 2008

One hundred ninety-three single-patient isolates of Escherichia coli harboring extended-spectrum β-lactamases (ESBL) were identified among 11 407 E. coli urine isolates recovered from single-patient outpatient urine cultures from 2003 to 2008. The percentage of ESBL-producing E. coli among community-onset E. coli urine isolates increased from 0.21% in 2003 to 2.99% in 2008. One hundred seven of the ESBL producers were positive for the presence of blaCTX-M genes. The percentage of CTX-M–producing E. coli rose from 0.07% in 2003 to 1.66% in 2008. The annual percentage of ESBL E. coli producing CTX-Ms changed from 35% in 2003 to 64% in 2008. Genes belonging to 3 blaCTX-M groups: blaCTX-M-1 group, blaCTX-M-2 group, and blaCTX-M-9 group, were detected. In addition, resistance to commonly used antimicrobial agents for community-acquired urinary tract infections was found common among CTX-M–producing E. coli isolates. Ertapenem and nitrofurantoin showed good in vitro activity against CTX-M producers.