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Antimicrobial Susceptibility to Azithromycin among Salmonella enterica Isolates from the United States
- Sjölund-Karlsson, Maria, Joyce, Kevin, Blickenstaff, Karen, Ball, Takiyah, Haro, Jovita, Medalla, Felicita M., Fedorka-Cray, Paula, Zhao, Shaohua, Crump, John A., Whichard, Jean M.
- Antimicrobial agents and chemotherapy 2011 v.55 no.9 pp. 3985-3989
- Salmonella enterica subsp. enterica serovar Typhi, ampicillin, antibacterial properties, antibiotic resistance, azithromycin, bacterial contamination, chloramphenicol, food animals, food contamination, humans, meat, minimum inhibitory concentration, salmonellosis, serotypes, sulfamethoxazole, trimethoprim
- 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.