Furtado G L, Medeiros A A
J Clin Microbiol. 1980 Oct;12(4):550-3. doi: 10.1128/jcm.12.4.550-553.1980.
The significance of the intermediate category of the single-disk diffusion test (Kirby-Bauer) of antibiotic susceptibility has never been clearly defined. Thirty-two percent of 756 clinical isolates of Proteus mirabilis were of intermediate susceptibility to chloramphenicol, a higher percentage than for any other species. The breakpoint separating susceptible and intermediate isolates nearly bisected the frequency distribution of zone diameters of P. mirabilis but not that of the other species. The breakpoint separating susceptible and intermediate isolates nearly bisected the frequency distribution of zone diameters of P. mirabillis but not that of the other species tested. By serial broth dilution testing, the minimal inhibitory concentrations (MICs) of chloramphenicol of 50 individual isolates of P. mirabilis were 3.9 to 22.1 micrograms/ml (geometric mean, 8.0), whereas the MICs of susceptible Escherichia coli, Klebsiella, and Enterobacter strains were 2.0 to 3.9 micrograms/ml (geometric mean, 2.9). Seventy percent of isolates of P. mirabilis with MICs of 7.8 to 15.6 micrograms/ml were classified as susceptible by disk testing. We conclude that existing Kirby-Bauer breakpoints do not accurately discriminate P. mirabilis isolates that are marginally susceptible to chloramphenicol. These data underscore the difficulty of applying a single set of breakpoints to all species and suggest that species-specific breakpoints would more accurately predict the MIC equivalent of given zone diameters.
抗生素敏感性单碟扩散试验（Kirby-Bauer试验）中“中介”类别（结果）的意义从未得到明确界定。在756株奇异变形杆菌临床分离株中，32%对氯霉素呈中介敏感性，这一比例高于其他任何菌种。区分敏感株与中介株的断点几乎将奇异变形杆菌抑菌圈直径的频率分布一分为二，但对其他菌种却并非如此。通过肉汤稀释系列试验，50株奇异变形杆菌分离株对氯霉素的最低抑菌浓度（MIC）为3.9至22.1微克/毫升（几何平均值为8.0），而敏感的大肠杆菌、克雷伯菌和肠杆菌菌株的MIC为2.0至3.9微克/毫升（几何平均值为2.9）。MIC为7.8至15.6微克/毫升的奇异变形杆菌分离株中，70%通过纸片试验被归类为敏感。我们得出结论，现有的Kirby-Bauer试验断点不能准确区分对氯霉素呈边缘敏感性的奇异变形杆菌分离株。这些数据凸显了对所有菌种应用单一断点的难度，并表明特定菌种的断点能更准确地预测给定抑菌圈直径对应的MIC。
