Suitable disk antimicrobial susceptibility breakpoints defining Salmonella enterica serovar Typhi isolates with reduced susceptibility to fluoroquinolones.

Abstract

Infections with Salmonella enterica serovar Typhi isolates that have reduced susceptibility to ofloxacin (MIC ≥ 0.25 μg/ml) or ciprofloxacin (MIC ≥ 0.125 μg/ml) have been associated with a delayed response or clinical failure following treatment with these antimicrobials. These isolates are not detected as resistant using current disk susceptibility breakpoints. We examined 816 isolates of S. Typhi from seven Asian countries. Screening for nalidixic acid resistance (MIC ≥ 16 μg/ml) identified isolates with an ofloxacin MIC of ≥0.25 μg/ml with a sensitivity of 97.3% (253/260) and specificity of 99.3% (552/556). For isolates with a ciprofloxacin MIC of ≥0.125 μg/ml, the sensitivity was 92.9% (248/267) and specificity was 98.4% (540/549). A zone of inhibition of ≤28 mm around a 5-μg ofloxacin disc detected strains with an ofloxacin MIC of ≥0.25 μg/ml with a sensitivity of 94.6% (246/260) and specificity of 94.2% (524/556). A zone of inhibition of ≤30 mm detected isolates with a ciprofloxacin MIC of ≥0.125 μg/ml with a sensitivity of 94.0% (251/267) and specificity of 94.2% (517/549). An ofloxacin MIC of ≥0.25 μg/ml and a ciprofloxacin MIC of ≥0.125 μg/ml detected 74.5% (341/460) of isolates with an identified quinolone resistance-inducing mutation and 81.5% (331/406) of the most common mutant (carrying a serine-to-phenylalanine mutation at codon 83 in the gyrA gene). Screening for nalidixic acid resistance or ciprofloxacin and ofloxacin disk inhibition zone are suitable for detecting S. Typhi isolates with reduced fluoroquinolone susceptibility.

• Authors: Christopher M Parry, Chau Tran Thuy, Sabina Dongol, Abhilasha Karkey, Ha Vinh, Nguyen Tran Chinh, Pham Thanh Duy, Tran Vu Thieu Nga, James I Campbell, Nguyen Van Minh Hoang, Amit Arjyal, Zulfiqar A Bhutta, Sujit K Bhattacharya, Magdarina D Agtini, Baiqing Dong, Do Gia Canh, Aliya Naheed, John Wain, Tran Tinh Hien, Buddha Basnyat, Leon Ochiai, John Clemens, Jeremy J Farrar, Christiane Dolecek, Stephen Baker
• Journal: Antimicrobial agents and chemotherapy (Antimicrob Agents Chemother) Vol. 54 Issue 12 Pg. 5201-8 (Dec 2010) ISSN: 1098-6596 [Electronic] United States
• PMID: 20837759 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anti-Bacterial Agents
• Bacterial Proteins
• Fluoroquinolones
• Nalidixic Acid
• Ciprofloxacin
• Ofloxacin
• DNA Topoisomerase IV
• DNA Gyrase

Topics

• Anti-Bacterial Agents (pharmacology)
• Bacterial Proteins (genetics)
• Ciprofloxacin (pharmacology)
• DNA Gyrase (genetics)
• DNA Topoisomerase IV (genetics)
• Drug Resistance, Bacterial
• Fluoroquinolones (pharmacology)
• Humans
• Microbial Sensitivity Tests
• Mutation (genetics)
• Nalidixic Acid (pharmacology)
• Ofloxacin (pharmacology)
• Salmonella typhi (drug effects, genetics)