Antimicrobial Susceptibility to Azithromycin among Salmonella enterica Isolates from the United States

National Antimicrobial Resistance Monitoring System, Centers for Disease Control and Prevention, CCID/NCZVED/DFBMD/EDLB, 1600 Clifton Road, Atlanta, GA 30329, USA.
Antimicrobial Agents and Chemotherapy (Impact Factor: 4.48). 06/2011; 55(9):3985-9. DOI: 10.1128/AAC.00590-11
Source: PubMed


Due to emerging resistance to traditional antimicrobial agents, such as ampicillin, trimethoprim-sulfamethoxazole, and chloramphenicol, azithromycin is increasingly used for the treatment of invasive Salmonella infections. In the present study, 696 isolates of non-Typhi Salmonella collected from humans, food animals, and retail meats in the United States were investigated for antimicrobial susceptibility to azithromycin. Seventy-two Salmonella enterica serotype Typhi isolates from humans were also tested. For each isolate, MICs of azithromycin and 15 other antimicrobial agents were determined by broth microdilution. Among the non-Typhi Salmonella isolates, azithromycin MICs among human isolates ranged from 1 to 32 μg/ml, whereas the MICs among the animal and retail meat isolates ranged from 2 to 16 μg/ml and 4 to 16 μg/ml, respectively. Among Salmonella serotype Typhi isolates, the azithromycin MICs ranged from 4 to 16 μg/ml. The highest MIC observed in the present study was 32 μg/ml, and it was detected in three human isolates belonging to serotypes Kentucky, Montevideo, and Paratyphi A. Based on our findings, we propose an epidemiological cutoff value (ECOFF) for wild-type Salmonella of ≤16 μg/ml of azithromycin. The susceptibility data provided could be used in combination with clinical outcome data to determine tentative clinical breakpoints for azithromycin and Salmonella enterica.

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Available from: Shaohua Zhao, Oct 16, 2014
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    • "Shirakawa et al. 42 had reported a high mutation rate of gyrA gene in S. Paratyphi A and such strains are resistant to nalidixic acid. Mutations in the gyrA gene that lead to quinolone resistance and reduced susceptibility to fluoroquinolones are clinically significant in S. Paratyphi A. Although azithromycin has been found to be efficacious for the treatment of uncomplicated typhoid fever 74, 75, 76, 77, 78, 79, high azithromycin MIC value and a case of azithromycin treatment failure in a patient with invasive S. Paratyphi A infection have been reported 80, 81. "
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