Salmonella is a leading cause of foodborne gastrointestinal illness in the United States; invasive infections require antimicrobial treatment with third-generation cephalosporins (e.g., ceftriaxone) and quinolones (e.g., ciprofloxacin) as first-line drugs. Presence of both extended-spectrum beta-lactamase (ESBL) phenotype and quinolone resistance is reported in <.2% of nontyphoidal Salmonella to CDC-National Antimicrobial Resistance Monitoring System. During May 2015, we investigated an outbreak of multidrug-resistant Salmonella serovar I 4,[5],12:i:- infections associated with consumption of Store A food in Wisconsin to stop transmission and understand multidrug-resistance mechanisms.
METHODS:
A confirmed case was defined as a Salmonella serovar I 4,[5],12:i:-infection with isolate pulsed-field gel electrophoresis patterns JPXX01.4356, JPXX01.4045, or JPXX01.0338; a probable case was a diarrheal illness in a person with exposure to Store A prepared foods during May 8–11. Laboratory investigation was enhanced by antimicrobial susceptibility testing, whole genome sequencing (WGS), and plasmid analysis of patient and food isolates.
RESULTS:
Seventy-six cases (37 confirmed and 39 probable) were identified; 7 (9%) hospitalizations and no deaths occurred. Seventy-three (96%) of 76 patients consumed Store A prepared pork carnitas.
All 37 patient isolates and 2 leftover prepared pork isolates were resistant to 9 antibiotics from 6 different antibiotic classes. All isolates were resistant to ceftriaxone; 36 isolates had intermediate ciprofloxacin resistance. WGS of a subset of isolates identified 13 resistance genes including blashv-12, a gene conferring ESBL phenotype, and aac(6’)-lb-cr, a plasmid-mediated quinolone resistance (PMQR) gene. Isolates with intermediate ciprofloxacin resistance also had PMQR qnrB49. Nine antibiotic resistance genes including blashv-12were plasmid encoded.
CONCLUSIONS:
Because plasmids permit horizontal gene transfer among different bacterial species, the potential for emerging multidrug-resistant Salmonella through plasmids warrants enhanced surveillance, investigation, and prevention.