Bradford P A, Sanders C C
Department of Medical Microbiology, Creighton University, Omaha, Nebraska 68178-0213.
Antimicrob Agents Chemother. 1993 Feb;37(2):251-9. doi: 10.1128/AAC.37.2.251.
A predictor panel of clinical isolates that produce a variety of types and amounts of beta-lactamases was used to assess the accuracies of a variety of susceptibility tests for ampicillin-sulbactam. Combinations of ampicillin-sulbactam in ratios of 1:1 and 2:1 and with sulbactam held constant at concentrations of 4 and 8 micrograms/ml were examined in dilution tests performed in agar and broth. In addition, disks containing 10/10, 20/10, 20/20, and 20/30 micrograms of ampicillin-sulbactam were examined in diffusion tests. The results indicated that the MICs obtained in broth microdilution tests performed with each of the four combinations differed, on average, less than twofold. Of the disks tested, the 20/10-micrograms ampicillin-sulbactam disk provided the best separation between susceptible and resistant strains when interpretive criteria for resistance was a zone size of < or = 16 mm and that for susceptibility was a zone size of > or = 21 mm. This disk also gave the highest overall agreement with MICs, regardless of the combination used in the broth microdilution test. Discrepancies between agar and broth microdilution MICs were greater than twofold, on average, and this necessitated recommendation of separate criteria for the two methods. Thus, a predictor panel was very useful in identifying the parameters of susceptibility tests that were most accurate in identifying strains that were susceptible and resistant to ampicillin-sulbactam.
使用一组能产生多种类型和数量β-内酰胺酶的临床分离株来评估多种氨苄西林-舒巴坦药敏试验的准确性。在琼脂和肉汤中进行的稀释试验中，检测了比例为1:1和2:1且舒巴坦浓度分别保持在4微克/毫升和8微克/毫升的氨苄西林-舒巴坦组合。此外，在扩散试验中检测了含有10/10、20/10、20/20和20/30微克氨苄西林-舒巴坦的药敏纸片。结果表明，用这四种组合中的每一种进行肉汤微量稀释试验所获得的最低抑菌浓度（MIC）平均差异不到两倍。在所测试的药敏纸片中，当耐药的判断标准为抑菌圈直径≤16毫米且敏感的判断标准为抑菌圈直径≥21毫米时，20/10微克的氨苄西林-舒巴坦药敏纸片在区分敏感菌株和耐药菌株方面表现最佳。无论肉汤微量稀释试验中使用哪种组合，该药敏纸片与MIC的总体一致性也最高。琼脂稀释法和肉汤微量稀释法的MIC之间的差异平均大于两倍，因此有必要针对这两种方法推荐不同的标准。因此，一组预测性分离株对于确定在识别对氨苄西林-舒巴坦敏感和耐药菌株方面最准确的药敏试验参数非常有用。
