title: Antimicrobial susceptibility to azithromycin among Salmonella enterica isolates from the United States.
abstract: 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.
authors.affiliation: National Antimicrobial Resistance Monitoring System, Centers for Disease Control and Prevention, CCID/NCZVED/DFBMD/EDLB, 1600 Clifton Road, Atlanta, GA 30329, USA. fwt4@cdc.gov
authors.forename: Maria
authors.initials: M
authors.lastname: Sjölund-Karlsson
authors.forename: Kevin
authors.initials: K
authors.lastname: Joyce
authors.forename: Karen
authors.initials: K
authors.lastname: Blickenstaff
authors.forename: Takiyah
authors.initials: T
authors.lastname: Ball
authors.forename: Jovita
authors.initials: J
authors.lastname: Haro
authors.forename: Felicita M
authors.initials: FM
authors.lastname: Medalla
authors.forename: Paula
authors.initials: P
authors.lastname: Fedorka-Cray
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zhao
authors.forename: John A
authors.initials: JA
authors.lastname: Crump
authors.forename: Jean M
authors.initials: JM
authors.lastname: Whichard
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017963:Azithromycin / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D019779:Salmonella enterica / Q000187:drug effects*; D014481:United States
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin