Fosfomycin Sensitivity Among Enterobacterales and Enterococci in Urine Culture in British Columbia, Canada, 2023-2024

Introduction: Fosfomycin is a commonly prescribed antimicrobial for the prevention and treatment of urinary tract infections. The current study aimed to show the fosfomycin sensitivity among Enterobacterales and enterococci urinary isolates in communities in British Columbia (BC), Canada. The population data will help clinicians in predicting the effectiveness of fosfomycin when patients’ urine isolate susceptibility results are pending.

Methods: LifeLabs BC regional microbiology laboratories, connected with 129 collection centres in urban and rural communities in the province, provided the laboratory data. An audit was conducted on all urine cultures from October 2023 to September 2024. Antimicrobial susceptibility testing was performed and interpreted using the Clinical and Laboratory Standard Institute M100 guidance. Breakpoints for Enterococcus faecalis and Escherichia coli were extrapolated to all enterococci and Enterobacterales, respectively. Species with <30 isolates tested were excluded to reduce the risk of selection bias.

Results:

Microorganisms (Susceptible Isolates/Total Number of Isolates = % Susceptible)

Enterobacter cloacae complex (16/65= 25%)

Enterococcus faecalis (249 / 266 = 94%)

Escherichia coli (49272/ 50329 = 98%)

Klebsiella oxytoca (32 / 62 = 52%)

Klebsiella pneumoniae (333 / 522 = 64%)

Proteus mirabilis (107 / 139 = 77%)

Vancomycin-resistant Enterococcus faecium (35 / 60 = 58%)

Vancomycin-sensitive Enterococcus faecium (55 / 112 = 49%)

Conclusion: Based on population data in BC, fosfomycin is likely effective against Enterococcus faecalis and Escherichia coli in urine (sensitivity >80%). Fosfomycin effectiveness is questionable against Klebsiella pneumoniae and Proteus mirabilis in urine (sensitivity 60-80%). It is likely ineffective against the Enterobacter cloacae complex, Klebsiella oxytoca, and Enterococcus faecium in urine (sensitivity <60%).