Jain Sanjay K, Gupta Amita, Glanz Brian, Dick James, Siberry George K
Division of Pediatric Infectious Diseases, Department of Pediatrics, School of Medicine, Johns Hopkins University, Baltimore, MD 21287, USA.
Pediatr Infect Dis J. 2005 Jun;24(6):494-7. doi: 10.1097/01.inf.0000164707.13624.a7.
Antimicrobial-resistant Shigella sonnei is a growing problem in the United States and poses treatment challenges particularly among children. Azithromycin is recommended as an alternative oral agent for shigellosis.
All isolates of Shigella submitted to Johns Hopkins clinical laboratory during the outbreak year (2002) were compared with a historical comparison group (1996-2000). Isolates were considered multiresistant if they were resistant to ampicillin and trimethoprim-sulfamethoxazole (TS). Selected outbreak and reference isolates were tested for azithromycin susceptibility by E-test, disk diffusion and broth dilution methods.
Between 1996-2000, among the 111 isolates submitted, 63% were from pediatric patients; 63% of isolates were resistant to ampicillin and 12% to TS. In 2002, among the 205 isolates submitted, 82% were from pediatric patients; 91% isolates were resistant to ampicillin and 67% to TS. The proportion of multiresistant isolates increased from 6% in 1996 to 65% in 2002 (P < 0.05). Azithromycin susceptibility by E-test and disk diffusion demonstrated 2 zones of inhibition for S. sonnei. Interpretation using the inner zone resulted in higher MICs (minimal inhibitory concentration) compared with the outer zones by E-test (P < 0.0001) and disk diffusion (P < 0.0001).
With increasing interest in using azithromycin for shigellosis, clinical laboratories should be aware of the interpretation difficulty caused by the dual-zone phenomenon seen with E-test and disk diffusion methods for S. sonnei.
在美国，耐抗生素的宋内志贺菌问题日益严重，尤其给儿童治疗带来挑战。阿奇霉素被推荐作为志贺菌病的替代口服药物。
将疫情爆发年（2002年）提交至约翰霍普金斯临床实验室的所有宋内志贺菌分离株与历史对照组（1996 - 2000年）进行比较。如果分离株对氨苄西林和甲氧苄啶 - 磺胺甲恶唑（TS）耐药，则被视为多重耐药。通过E试验、纸片扩散法和肉汤稀释法对选定的疫情爆发和参考分离株进行阿奇霉素敏感性测试。
1996 - 2000年期间，提交的111株分离株中，63%来自儿科患者；63%的分离株对氨苄西林耐药，12%对TS耐药。2002年，提交的205株分离株中，82%来自儿科患者；91%的分离株对氨苄西林耐药，67%对TS耐药。多重耐药分离株的比例从1996年的6%增加到2002年的65%（P < 0.05）。通过E试验和纸片扩散法检测阿奇霉素敏感性时，宋内志贺菌出现了两个抑菌圈。与E试验（P < 0.0001）和纸片扩散法（P < 0.0001）的外圈相比，使用内圈进行解读时，最低抑菌浓度（MIC）更高。
随着对使用阿奇霉素治疗志贺菌病的兴趣增加，临床实验室应意识到E试验和纸片扩散法对宋内志贺菌出现的双圈现象所导致的解读困难。
