Background/Aim
Escherichia coli and Klebsiella pneumoniae are two of the most common urinary pathogens worldwide. With increasing antibiotic resistance, the oral drug fosfomycin, which is not commonly used in Singapore, may be a potential therapeutic option for multi-drug resistant E.coli and K. pneumoniae. This study aimed to
(a) evaluate the effectiveness of Fosfomycin against multi-drug resistant strains of E.coli and K. pneumoniae urinary pathogens
(b) evaluate the accuracy of existing disk diffusion breakpoints against the gold standard agar dilution method
Materials and Methods.
Multi-resistant urinary isolates of E.coli (n=106) and K. pneumoniae (n=91) were collected over a period of about 5 months. These were screened for ESBL and AmpC genes by PCR and disc diffusion. Susceptibility testing of fosfomycin was performed by agar dilution (test concentrations 0.5-256 µg/ml), with categorial susceptibility interpreted using CLSI breakpoints (S≤64, R>256). Disc diffusion testing using CLSI methodology was interpreted using CLSI breakpoints and those from Lu, et al., and discordant results categorized as minor errors (Mi) or major/very major errors (Mj/VMj).
Results
78.7% of E. coli isolates were susceptible to fosfomycin compared with 73.7% of K. pneumoniae. Beta-lactamase genes were present in 57 E. coli isolates (ESBL=25, ampC=32), and 90 K. pneumoniae isolates (ESBL=43,ampC=47). When disc inhibition zones were analysed using CLSI criteria, there were 5.2% Mi, Mj and VMj error compared with 6.6% Mi, Mj and VMj error when using the criteria by Lu, et al.
Conclusion
Fosfomycin proved to be a potential alternative antibiotic to treat patients with urinary tract infections, even against multi-drug resistant E.coli and K. pneumoniae. E. coli were found to be more susceptible to fosfomycin as compared to K. pneumoniae which showed more resistance. CLSI criteria were preferred over Lu, et al.