Pottumarthy Sudha, Deshpande Lalitagauri M, Sader Helio S, Jones Ronald N
JMI Laboratories, North Liberty, IA 52317, USA.
Diagn Microbiol Infect Dis. 2005 Jun;52(2):95-9. doi: 10.1016/j.diagmicrobio.2004.12.004.
To reassess the validity of existing susceptibility breakpoint criteria and to propose alternative breakpoint criteria for disk diffusion testing at lower susceptible MIC breakpoints, we analyzed a contemporary global collection of Enterobacteriaceae isolates (350) strains enriched for extended-spectrum beta-lactamase (ESBL) producers (68 strains, 19.4%). The majority of the isolates (88.3% of the entire collection and 83.8% of the ESBL subset) were from bloodstream infections. Cefepime minimal inhibitory concentrations (MICs) were determined by broth microdilution methods and compared with the results obtained from disk diffusion testing for the entire collection of Enterobacteriaceae and for the ESBL subset alone. The regression coefficient was excellent for both scattergrams (r = 0.92-0.94). The intermethod categorical agreement remained excellent for the current breakpoints (susceptible at < or = 8 microg/mL or > or = 18 mm and resistant at > or = 32 microg/mL or < or = 14 mm) published by the National Committee for Clinical Laboratory Standards at 94.0%. The 2 alternative interpretive criteria considered at lower MIC breakpoints (i.e., susceptible as < or = 4 microg/mL and > or = 21 mm and susceptible as < or = 2 microg/mL and > or = 24 mm) did not compromise the intermethod test categorical accuracy, which remained excellent at 96.9% and 94.0%, respectively. Adopting the existing breakpoint criteria that remain accurate for ESBL-producing strains or any one of the above two alternative sets of breakpoint criteria analyzed would be acceptable, with excellent intermethod concordance between the MIC and disk diffusion results.
为重新评估现有药敏折点标准的有效性，并针对较低敏感 MIC 折点的纸片扩散法检测提出替代折点标准，我们分析了一组当代全球收集的肠杆菌科分离株（350 株），其中富含超广谱β-内酰胺酶（ESBL）产生菌（68 株，占 19.4%）。大多数分离株（占整个收集菌株的 88.3%以及 ESBL 亚组的 83.8%）来自血流感染。通过肉汤微量稀释法测定头孢吡肟的最低抑菌浓度（MIC），并将其与整个肠杆菌科收集菌株以及单独的 ESBL 亚组的纸片扩散法检测结果进行比较。两个散点图的回归系数都非常好（r = 0.92 - 0.94）。对于美国国家临床实验室标准委员会公布的当前折点（≤8 μg/mL 或≥18 mm 为敏感，≥32 μg/mL 或≤14 mm 为耐药），方法间分类一致性仍非常好，为 94.0%。在较低 MIC 折点考虑的两个替代解释标准（即≤4 μg/mL 且≥21 mm 为敏感，≤2 μg/mL 且≥24 mm 为敏感）并未损害方法间检测分类准确性，分别仍保持在 96.9%和 94.0%的高水平。采用对产 ESBL 菌株仍然准确的现有折点标准或上述分析的两组替代折点标准中的任何一组都是可以接受的，MIC 和纸片扩散法结果之间的方法间一致性非常好。
