Comparison of the MicroScan system and the agar dilution assay for Quinupristin/Dalfopristin susceptibility of Enterococcus faecium.
We compared the results of Quinupristin/Dalfopristin (Q/D) susceptibility tests by the Positive Combo Panel (Type 11) of the MicroScan Walk Away 96 analyzer (Dade Behring, Inc.) with those obtained by the reference agar dilution method. From September 2003 to August 2004, a total of 410 E. faecium isolates were obtained from clinical samples. Of these, 65 (15.9%) strains were non-susceptible, and 345 (84.1%) strains were susceptible to Q/D. We collected consecutively 65 Q/D non-susceptible E. faecium isolates (42 resistant, 23 intermediate), and randomly selected 32 Q/D susceptible E. faecium isolates using the MicroScan system. The minimal inhibitory concentrations (MICs) of Q/D, vancomycin, and teicoplanin were determined by the agar dilution method according to CLSI guidelines. The agreement rates between the two methods were 100% for Q/D-susceptible strains, 85.7% for Q/D-resistant strains, and 26.1% for Q/D-intermediate strains of E. faecium. The major error rate (S-->R) was 11.9%, and the minor error rate (S-->I) was 13.0%. No very major errors were found. We conclude that for MicroScan 'non-susceptible' test results for Q/D, it is necessary to confirm the result using a reference method. The Q/D-resistance rate was higher in glycopeptide-susceptible (78.0% for vancomycin, 82.0% for teicoplanin) than glycopeptide-resistant E. faecium (22.0% for vancomycin, 16.0% for teicoplanin). Further studies are needed to determine whether Q/D use in hospitals or virginiamycin use in animals, or other factors, are responsible for the high rates of glycopeptide-susceptible and Q/D-resistant E. faecium strains in Korea.
Kim
Yang-Ree
YR
Department of Internal Medicine, Uijeongbu St Mary's Hospital, Uijeongbu, Korea.
Kim
Sang-Il
SI
Hur
Ji-Ahn
JA
Kim
Youn-Jeong
YJ
Wie
Seong-Heon
SH
Park
Yeon-Joon
YJ
Kang
Moon-Won
MW
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004352:Drug Resistance, Microbial; D016984:Enterococcus faecium / Q000187:drug effects* / Q000254:growth & development; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D015203:Reproducibility of Results; D017334:Teicoplanin / Q000494:pharmacology; D014640:Vancomycin / Q000494:pharmacology; D014769:Virginiamycin / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D017334:Teicoplanin; D014640:Vancomycin