Kapil Arti, Das Bimal
Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
Indian J Med Res. 2002 Feb;115:49-54.
BACKGROUND & OBJECTIVES: Clinical non response to ciprofloxacin therapy in enteric fever is increasingly being encountered in endemic areas possibly due to the increase in the levels of resistance to ciprofloxacin in Salmonella typhi. The antimicrobial susceptibility tests for S. typhi performed by the disc diffusion method using NCCLS breakpoints fail to detect the increasing MIC of ciprofloxacin, leading to the inappropriate treatment of enteric fever with ciprofloxacin. We explored the possibility of testing S. typhi strains for their susceptibility to nalidixic acid by disc diffusion method as a marker for high MIC to ciprofloxacin.
Isolates (94) of S. typhi were tested for in vitro susceptibility to nalidixic acid (30 micrograms) and ciprofloxacin (5 micrograms) by disc diffusion method using NCCLS guidelines. The MIC of these strains to ciprofloxacin was also determined by E-test.
Of the 94 strains tested, 56 were NARST (nalidixic acid resistant S. typhi) and 34 were NASST (nalidixic acid sensitive S. typhi). MIC of ciprofloxacin in the NASST strains varied from 0.002-0.125 microgram/ml while that for NARST strains varied from 0.023-0.38 microgram/ml, which is about 10-folds higher than that of NASST strains.
INTERPRETATION & CONCLUSION: Our study shows that resistance to nalidixic acid is associated with a high MIC to ciprofloxacin in S. typhi. These strains would have been interpreted as ciprofloxacin sensitive by routine antimicrobial susceptibility testing by disc diffusion method. Hence screening of S. typhi isolates by the nalidixic acid susceptibility test may be incorporated in a clinical bacteriology laboratory to alert the treating physicians of the possibility of the failure to ciprofloxacin therapy in patients with enteric fever.
在伤寒流行地区,临床对环丙沙星治疗无反应的情况日益常见,这可能是由于伤寒沙门菌对环丙沙星的耐药水平增加所致。采用美国国家临床实验室标准化委员会(NCCLS)标准通过纸片扩散法进行的伤寒沙门菌药敏试验无法检测到环丙沙星不断升高的最低抑菌浓度(MIC),导致用环丙沙星对伤寒进行不恰当的治疗。我们探讨了通过纸片扩散法检测伤寒沙门菌菌株对萘啶酸的敏感性作为环丙沙星高MIC的标志物的可能性。
按照NCCLS指南,采用纸片扩散法对94株伤寒沙门菌分离株进行体外对萘啶酸(30微克)和环丙沙星(5微克)的敏感性检测。这些菌株对环丙沙星的MIC也通过E试验测定。
在检测的94株菌株中,56株为萘啶酸耐药伤寒沙门菌(NARST),34株为萘啶酸敏感伤寒沙门菌(NASST)。NASST菌株中环丙沙星的MIC为0.002 - 0.125微克/毫升,而NARST菌株的MIC为0.023 - 0.38微克/毫升,约为NASST菌株的10倍。
我们的研究表明,伤寒沙门菌对萘啶酸耐药与环丙沙星的高MIC相关。通过常规纸片扩散法进行的药敏试验会将这些菌株判定为对环丙沙星敏感。因此,临床细菌学实验室可采用萘啶酸药敏试验对伤寒沙门菌分离株进行筛查,以提醒治疗医生伤寒患者使用环丙沙星治疗可能失败。