In vitro susceptibility of urinary Escherichia coli isolates to first- and second-line empirically prescribed oral antimicrobials: CANWARD surveillance study results for Canadian outpatients, 2007–2016

• Published in: International journal of antimicrobial agents Vol. 54; no. 1; pp. 62 - 68
• Main Authors: Karlowsky, James A., Lagacé-Wiens, Philippe R.S., Adam, Heather J., Baxter, Melanie R., Laing, Nancy M., Walkty, Andrew J., Zhanel, George G.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.07.2019
• Subjects: CANWARD; Escherichia coli; Outpatient; Susceptibility; Urine; Urine; Outpatient; CANWARD; Susceptibility; Escherichia coli
• ISSN: 0924-8579; 1872-7913
• DOI: 10.1016/j.ijantimicag.2019.04.012

•99.2% of Escherichia coli isolates were susceptible to fosfomycin.•97.5% of E. coli isolates were susceptible to nitrofurantoin.•<80% of E. coli isolates were susceptible to trimethoprim/sulfamethoxazole.•ESBL rates for E. coli isolates increased between 2007 (0.8%) and 2016 (10.1%).•MDR rates for E. coli isolates increased between 2007 (9.7%) and 2016 (16.5%). Escherichia coli isolates (n = 2035) from urine specimens of outpatients presenting to Canadian medical clinics and hospital emergency departments from 2007–2016 were collected as part of the CANWARD surveillance study. Isolate identification and antimicrobial susceptibility testing (AST) were performed at a central site (Health Sciences Centre, Winnipeg, Canada). AST of first- and second-line oral antimicrobial agents was performed using CLSI methods (M07, 11th ed, 2018); fosfomycin was tested by agar dilution and all other agents by broth microdilution. Minimum inhibitory concentrations (MICs) were interpreted using CLSI M100 (2018) criteria. Fosfomycin (99.2% of isolates susceptible), nitrofurantoin (97.5%) and cefalexin (93.6%) were the most active agents tested; amoxicillin/clavulanic acid (AMC) (85.6%), ciprofloxacin (83.0%) and trimethoprim/sulfamethoxazole (SXT) (77.0%) were less active. Annual percentages of isolates positive for extended-spectrum β-lactamases (ESBLs) or demonstrating multidrug-resistant (MDR) phenotypes increased from 0.8% (2007) to 10.1% (2016), and from 9.7% (2007) to 16.5% (2016), respectively, whilst the annual frequency of AmpC-positive isolates decreased from a high of 3.2% in 2008 to 0.7% in 2016. The most common MDR phenotype of E. coli was non-susceptibility to AMC, ciprofloxacin, and SXT, accounting for 12.7% (26/205) of all MDR isolates. Rates of susceptibility were higher for fosfomycin than for the five other oral agents tested against ESBL-positive (96.1% susceptible) and MDR (95.1%) isolates and were equal to nitrofurantoin (96.4%) against AmpC-positive isolates. Prudent use of antimicrobials and close monitoring of antimicrobial susceptibilities of clinical uropathogenic E. coli isolates are imperative to help preserve the utility of oral antimicrobials.