An interprovincial external quality assessment of the ability of Canadian laboratories to detect the vancomycin and penicillin resistance of Enterococcus faecium D366.

OBJECTIVE

To evaluate the ability of Canadian laboratories to identify enterococci and detect low-level resistance to penicillin, ampicillin and vancomycin in five provinces and two territories by two external quality assessment schemes.

METHODS

Enterococcus faecium, strain D366, with minimum inhibitory concentrations for vancomycin and penicillin of 32 and 16 mg/L respectively, was distributed during a routine proficiency survey. Laboratories were required to culture and identify the isolate and to test antimicrobial susceptibility. Participants were assessed against consensus reference values.

RESULTS

Three hundred and sixty-four hospital, commercial and public-health laboratories participated, using their established procedures for patient samples. The isolate was identified to the species level by 222 (61%) laboratories and to the genus level by a further 98 participants. Forty-four failed to meet the expected standard. Vancomycin resistance was detected by 94%. Those reporting a falsely susceptible result used disk diffusion testing. Penicillin resistance was noted by 250 of 258 laboratories reporting on this agent. An incorrect ampicillin-susceptible finding was reported by 62 of 147 laboratories using automated microdilution or agar dilution methods.

CONCLUSIONS

Most laboratories identified the isolate to an appropriate level. Detection of low-level vancomycin and penicillin resistance was achieved by the majority. Ampicillin resistance was less readily detected.