Uete G, Matsuo K, Uete T
Department of Clinical Investigation, Kitano Hospital, Tazuke Kofukai Medical Research Institute, Osaka.
Jpn J Antibiot. 1989 Sep;42(9):1888-99.
The reliability of the tobramycin (TOB) disc susceptibility test in estimating approximate values of MICs was studied using various clinical isolates totaling 261 strains and using Showa discs (8 mm diameter containing 30 micrograms of TOB) and Difco discs (6 mm diameter containing 10 micrograms of TOB). Clinical significance of a 4 category system for the interpretation of the disc tests, which is widely used in Japan, and that of a 3 category system used in USA and Europe, were also evaluated to determine which system would be more suitable for the evaluation of proper dose levels of administration. Furthermore, the evaluation was made using these discs with respect to the in vitro MIC break points for therapeutic use of antibiotics proposed by the British Society for Antimicrobial Chemotherapy (J. Antimicr. Chemoth. 21:701-710, 1988). The results obtained with the disc method were compared with MICs determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The results of the TOB disc susceptibility test either with Showa or Difco discs were well correlated with MICs, showing the reliability of the disc method to estimate approximate values of MICs. Break points in MIC values proposed for the classification of bacteria into the 4 categories of susceptibility are () MIC less than or equal to 2 micrograms/ml, (++) MIC greater than 2-10 micrograms/ml, (+) MIC greater than 10-50 micrograms/ml, (-) MIC greater than 50 micrograms/ml. Those proposed in the 3 categories of susceptibility are Sensitive (S) MIC less than or equal to 4 micrograms/ml, Intermediate (I) MIC greater than 4-8 micrograms/ml, Resistance (R) MIC greater than 8 micrograms/ml. In the 4 category classification system of the Showa disc susceptibility test, 16 out of 261 strains (6.1%) tested showed false positive results and 7 (2.7%) did false negative results. If the classification was modified as follows: ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml, false positive results were markedly reduced. Only 6 out of 261 strains (2.3%) showed false positive results, and 7 (2.7%) did false negative results. With Difco disc, in the 4 category interpretation system, 8 out of 261 strains (3.1%) tested showed false positive and 35 (13.4%) did false negative results. No inhibitory zones were observed against a majority of strains with MIC greater than 25 micrograms/ml, thus unable to assess (+) susceptibility.(ABSTRACT TRUNCATED AT 400 WORDS)
使用总共261株不同的临床分离菌株，采用昭和药敏纸片（直径8 mm，含30微克妥布霉素）和迪夫科药敏纸片（直径6 mm，含10微克妥布霉素），研究了妥布霉素（TOB）纸片药敏试验在估计最低抑菌浓度（MIC）近似值方面的可靠性。还评估了在日本广泛使用的用于解释纸片试验的4分类系统以及在美国和欧洲使用的3分类系统的临床意义，以确定哪种系统更适合评估合适的给药剂量水平。此外，使用这些纸片对抗菌化疗英国协会提出的抗生素治疗用体外MIC折点进行了评估（《抗菌化疗杂志》21:701 - 710, 1988）。将纸片法获得的结果与接种量为10(6) CFU/ml时使用琼脂稀释法测定的MIC进行比较。使用昭和或迪夫科纸片进行的TOB纸片药敏试验结果与MIC相关性良好，表明纸片法在估计MIC近似值方面的可靠性。用于将细菌分为4类药敏的MIC值折点为：（）MIC小于或等于2微克/毫升，（++）MIC大于2 - 10微克/毫升，（+）MIC大于10 - 50微克/毫升，（ - ）MIC大于50微克/毫升。3类药敏中提出的折点为：敏感（S）MIC小于或等于4微克/毫升，中介（I）MIC大于4 - 8微克/毫升，耐药（R）MIC大于8微克/毫升。在昭和纸片药敏试验的4分类系统中，261株受试菌株中有16株（6.1%）出现假阳性结果，7株（2.7%）出现假阴性结果。如果将分类修改如下：（）MIC小于或等于3微克/毫升，（++）MIC大于3 - 15微克/毫升，（+）MIC大于15 - 60微克/毫升，（ - ）MIC大于60微克/毫升，则假阳性结果明显减少。261株中只有6株（2.3%）出现假阳性结果，7株（2.7%）出现假阴性结果。对于迪夫科纸片，在4分类解释系统中，261株受试菌株中有8株（3.1%）出现假阳性，35株（13.4%）出现假阴性结果。对于大多数MIC大于25微克/毫升的菌株未观察到抑菌圈，因此无法评估（+）药敏情况。（摘要截于400字）
