Evaluation of E test, disk diffusion and broth microdilution to establish tentative quality control limits and review susceptibility breakpoints for two aerobic actinomycetes.
A single laboratory study was carried out to compare E Test with broth microdilution and disk diffusion to establish tentative quality control ranges for Nocardia asteroides ATCC 19247 and Rhodococcus equi ATCC 6939 against a panel of eight antimicrobial agents. Reproducibility testing was performed on 12 consecutive days to establish tentative quality control ranges. A total of 36 clinical strains of the Nocardia asteroides complex and 5 Rhodococcus strains were used in the study. Both candidate control strains and clinical strains grew well on cation-adjusted Mueller-Hinton agar. Adequate growth occurred at 48 to 72 h for the Nocardia isolates and 24 to 48 h for Rhodococcus. A standardized primary inoculum of 5 x 10(4) CFU/mL was used for performance of E Test and disk diffusion for the Nocardia isolates. Tentative population-based error rates were calculated using current breakpoints for Enterobacteriaceae for E Test compared with disk diffusion for the 36 clinical strains of Nocardia species. Significant very major error rates were observed for imipenem (22%) and minor error rates varied from 2.7% to 50%. These methods require more extensive validation before definitive breakpoint criteria can be established.
Tomlin
P
P
Microbiology and Public Health, and National Centre for Mycology, University of Alberta Hospital, Edmonton, Alberta, Canada T6G 2J2.
Sand
C
C
Rennie
R P
RP
D000332:Aerobiosis; D003470:Culture Media; D004058:Diffusion; D008826:Microbial Sensitivity Tests / Q000379:methods* / Q000592:standards; D009615:Nocardia / Q000187:drug effects*; D011786:Quality Control; D015203:Reproducibility of Results; D012240:Rhodococcus / Q000187:drug effects*
D003470:Culture Media