Pfaller M A, Wakefield D S, Stewart B, Bale M, Hammons G T, Massanari R M
Veterans Administration Medical Center, Iowa City, Iowa.
Am J Clin Pathol. 1988 Jan;89(1):120-5. doi: 10.1093/ajcp/89.1.120.
The purpose of this study was to examine the efficacy of the oxacillin disk diffusion test and the methicillin and oxacillin agar screen tests as predictors of oxacillin resistance as defined by the reference broth microdilution method. A total of 444 clinical isolates of Staphylococcus aureus collected from individual patients over a four-year period were tested by (1) the oxacillin disk diffusion test, with particular attention to the presence of fine growth of a resistant subpopulation within the zone of inhibition (Ox Grow interpretive criteria); (2) the agar screen method using agar plates with 4% NaCl and either 6 mg/L oxacillin or 10 mg/L methicillin; and (3) the oxacillin and methicillin broth microdilution test methods with 2% NaCl supplementation. Overall, 62 (14%) isolates were resistant and 382 (86%) isolates were susceptible to oxacillin with the use of the reference broth microdilution system. The results indicate that the disk diffusion test with the use of the Ox Grow criteria had a high sensitivity (94%) and negative predictive value (98%) but a low specificity (67%) and positive predictive value (32%) when compared with the reference broth dilution test. Similarly, the agar screen tests had a high sensitivity (95-97%) and negative predictive values (99%) but low specificity (64-74%) and positive predictive values (30-37%). These data indicate that the agar screen tests and the oxacillin disk test with the use of the Ox Grow interpretive criteria may be useful as screening tests for detecting resistance to the penicillinase-resistant penicillins but that all resistant isolates should be confirmed by the reference broth dilution method because of the large number of false-resistant screening test results.
本研究的目的是检验苯唑西林纸片扩散试验、甲氧西林和苯唑西林琼脂筛选试验作为参照肉汤微量稀释法所定义的苯唑西林耐药性预测指标的有效性。在四年期间从个体患者收集的444株金黄色葡萄球菌临床分离株通过以下方法进行检测：（1）苯唑西林纸片扩散试验，特别关注抑菌圈内耐药亚群的细微生长情况（Ox Grow解释标准）；（2）使用含4%氯化钠以及6 mg/L苯唑西林或10 mg/L甲氧西林的琼脂平板的琼脂筛选法；（3）补充2%氯化钠的苯唑西林和甲氧西林肉汤微量稀释试验方法。总体而言，使用参照肉汤微量稀释系统时，62株（14%）分离株对苯唑西林耐药，382株（86%）分离株对苯唑西林敏感。结果表明，与参照肉汤稀释试验相比，采用Ox Grow标准的纸片扩散试验具有较高的敏感性（94%）和阴性预测值（98%），但特异性较低（67%）和阳性预测值较低（32%）。同样，琼脂筛选试验具有较高的敏感性（95 - 97%）和阴性预测值（99%），但特异性较低（64 - 74%）和阳性预测值较低（30 - 37%）。这些数据表明，琼脂筛选试验和采用Ox Grow解释标准的苯唑西林纸片试验作为检测对耐青霉素酶青霉素耐药性的筛选试验可能有用，但由于大量假耐药筛选试验结果，所有耐药分离株均应通过参照肉汤稀释法进行确认。
