Quality control for beta-lactam susceptibility testing with a well-defined collection of Enterobacteriaceae and Pseudomonas aeruginosa strains in Spain.
Eighteen Enterobacteriaceae and Pseudomonas aeruginosa strains, 16 of them with well-defined beta-lactam resistance mechanisms, were sent to 52 Spanish microbiology laboratories. Interpretative categories for 8 extended-spectrum beta-lactams were collected. Participating laboratories used their own routine susceptibility testing procedures (88% automatic systems, 10% disk diffusion, and 2% agar dilution). Control results were established by two independent reference laboratories by applying the NCCLS microdilution method and interpretative criteria. Interpretative discrepancies were observed in 16% of the results (4.4% for cefepime, 3.0% for aztreonam, 2.8% for piperacillin-tazobactam, 1.7% for cefotaxime [CTX] and ceftazidime, 1.1% for ceftriaxone, 0.9% for meropenem, and 0.3% for imipenem). High consistency with reference values (<5% of major plus very major errors) was observed with (i) American Type Culture Collection quality control strains; (ii) strains with low-efficiency mechanisms inactivating extended-spectrum beta-lactams, such as OXA-1-producing Escherichiacoli or SHV-1-hyperproducing Klebsiella pneumoniae; (iii) strains with highly efficient mechanisms, such as SHV-5 porin-deficient K. pneumoniae, CTX-M-10 in Enterobacter cloacae hyperproducing AmpC, and P. aeruginosa with the MexAB OprM efflux phenotype or hyperproducing AmpC. Low consistency (>30% major plus very major errors) was detected in K1-producing Klebsiella oxytoca, CTX-M-9-producing E. coli, and in OprD(-) P. aeruginosa strains. Extended-spectrum beta-lactamase (ESBL)-producing strains accounted for 86% of very major errors. Recognition of the ESBL phenotype was particularly low in Enterobacter cloacae strains (<35%), due to the lack of NCCLS-specific rules in this genus. A K1-producing K. oxytoca was misidentified by 10% of laboratories as an ESBL producer. The use of well-defined resistant strains is useful for improving proficiency in susceptibility testing in clinical laboratories.
Servicio de Microbiología, Hospital Universitario Ramón y Cajal, 28034 Madrid. rcanton.hrc@salud.madrid.org
Rafael
R
Cantón
Elena
E
Loza
María
M
Del Carmen Conejo
Fernando
F
Baquero
Luis
L
Martínez-Martínez
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D066298:In Vitro Techniques; D007753:Laboratories; D008826:Microbial Sensitivity Tests / Q000592:standards*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000201:enzymology; D011786:Quality Control; D013030:Spain; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000096:biosynthesis; D047090:beta-Lactams
D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases