Extra-intestinal pathogenic Escherichia coli (ExPEC) is one of the most common causes of BSIs in North America. Studies show that 20-45% of ExPEC are resistant to first line antibiotic therapies, and the frequency of extended spectrum beta-lactamases (ESBLs) is increasing. Our surveillance data in Calgary, Alberta, Canada demonstrates a steady increase in the incidence of E.coli BSIs and antibiotic resistance in our population, most markedly since 2007. This study aims to assess our current burden of ExPEC BSIs and the evolving antibiotic resistance patterns.
Adult and pediatric blood cultures processed at a centralized laboratory between January 1, 2016 and December 31, 2016 were eligible for inclusion. Patients with blood cultures positive for E.coli were retrospectively identified and antibiotic susceptibility profiles were retrieved using laboratory software. Antibiotic susceptibilities were determined using CLSI breakpoints for Enterobacteriaceae. The presence of ESBLs was confirmed by CLSI disk confirmation testing.
There were a total of 748 confirmed sets of positive blood cultures for E.coli. Thirty-six duplicates were removed, for a total of 712 unique patient isolates. Only 298 isolates (41.9%) were susceptible to all antibiotics tested, with the remaining isolates demonstrating variable resistance to all other antibiotic classes including ampicillin (53.7%), amoxicillin-clavulanic acid (7.6%), piperacillin-tazobactam (1.1%), cefazolin (23.9%), ciprofloxacin (27.9%), and trimethoprim-sulfamethoxazole (33.3%). 120 ESBL-producing organisms were identified (16.9%). Of these, many had additional resistance to ciprofloxacin (51.7%), trimethoprim-sulfamethoxazole (55%), and carbapenems (1.7%).
ExPEC is a common cause of BSIs in our patient population, and a particularly concerning finding is the presence of multi-drug resistance to cephalosporins, fluoroquinolones, and trimethoprim-sulfamethoxazole in a number of isolates. Detailed epidemiological studies are required to characterize key microbial and clinical factors driving antibiotic resistance of E.coli in our population and will be relevant to clinical practice, informing local guidelines on empiric antibiotic choices.
M. S. Holland,
D. Church, None
J. Pitout, None