Zafar Afia, Ibrahim Nazish Gul, Ahsan Tanwir, Abbas Zohair, Zaidi Anita, Hasan Rumina
Department of Pathology and Microbiology, The Aga Khan University Hospital, Karachi.
J Coll Physicians Surg Pak. 2005 Jul;15(7):413-7.
To determine the validity of nalidixic acid screening test in the detection of high MICs of fluoroquinolone against Salmonella(S.) typhi isolated from blood and correlate zone diameters of ofloxacin with that of MIC value for nalidixic acid sensitive and resistant strains.
Cross-sectional analytical study.
Clinical Microbiology Laboratory of the Aga Khan Hospital, Karachi from January 2002 to December 2003.
Two hundred S. typhi isolates from blood were included for nalidixic acid screening and ofloxacin susceptibility. Antibiotic susceptibilities for both the antibiotics were obtained by disc diffusion method whereas MICs were determined by standard agar dilution method as recommended by NCCLS guidelines. Sensitivity, specificity and correlation between both antimicrobial susceptibility methods were calculated and results expressed as scattergrams.
The results broadly classify S. typhi isolates into nalidixic acid resistant strains with no zone of inhibition around 30 mug nalidixic acid disc and nalidixic acid sensitive strains with mean zone of inhibition of 24.9 mm. All S. typhi isolates with ofloxacin MIC of capital ZHE, Cyrillic 0.125 microg/ml were found to be nalidixic acid resistant (MIC capital ZHE, Cyrillic32 microg/ml) whereas the isolates with ofloxacin MIC 0.06 microg/ml were nalidixic acid sensitive (MIC 8 microg/ml). Screening for nalidixic acid resistance was found to be 100% sensitive and 97% specific in identifying S. typhi strains with reduced susceptibility to fluoroquinolone (MIC capital ZHE, Cyrillic 0.125 microg/ml).
Nalidixic acid resistance as a screening method is proved to be significant in identifying S. typhi isolates with reduced susceptibility to fluoroquinolones. It is also suggested that inhibition zone of 25 mm around 5 microg ofloxacin disc is appropriate as a selection criterion to detect S. typhi isolates with reduced susceptibility to fluoroquinolones.
确定萘啶酸筛选试验在检测从血液中分离出的伤寒沙门菌对氟喹诺酮类药物的高最低抑菌浓度（MIC）方面的有效性，并将氧氟沙星的抑菌圈直径与萘啶酸敏感和耐药菌株的MIC值进行关联。
横断面分析研究。
2002年1月至2003年12月在卡拉奇阿迦汗医院临床微生物实验室。
纳入200株从血液中分离出的伤寒沙门菌进行萘啶酸筛选和氧氟沙星敏感性检测。两种抗生素的药敏试验采用纸片扩散法，而MIC则按照美国国家临床实验室标准委员会（NCCLS）指南推荐的标准琼脂稀释法测定。计算两种药敏方法之间的敏感性、特异性和相关性，并将结果以散点图表示。
结果大致将伤寒沙门菌分离株分为对30μg萘啶酸纸片周围无抑菌圈的萘啶酸耐药菌株和平均抑菌圈为24.9mm的萘啶酸敏感菌株。所有氧氟沙星MIC为0.125μg/ml的伤寒沙门菌分离株均被发现对萘啶酸耐药（MIC为32μg/ml），而氧氟沙星MIC为0.06μg/ml的分离株对萘啶酸敏感（MIC为8μg/ml）。在鉴定对氟喹诺酮类药物敏感性降低（MIC为0.125μg/ml）的伤寒沙门菌菌株时，萘啶酸耐药筛选的敏感性为100%，特异性为97%。
萘啶酸耐药作为一种筛选方法，在鉴定对氟喹诺酮类药物敏感性降低的伤寒沙门菌分离株方面被证明具有重要意义。还建议以5μg氧氟沙星纸片周围25mm的抑菌圈作为检测对氟喹诺酮类药物敏感性降低的伤寒沙门菌分离株的选择标准是合适的。
