Background
Antimicrobial resistance in foodborne pathogens, including non-typhoidal Salmonella (NTS), is a public health concern. Pennsylvania conducts integrated surveillance for antimicrobial resistance in NTS from human and animal sources.
Methods
During 2015-2017, clinical laboratories submitted 4,478 NTS isolates from humans and 96 isolates were found in 2,520 retail meat samples. One hundred and nine clinical isolates that shared pulsed-field gel electrophoresis patterns with meat isolates and all strains from meat samples were tested for susceptibility to antimicrobial agents. Six clinical and 96 NTS isolates from meat sources (total 102) were analyzed by whole-genome sequencing (WGS).
Results
28 (25.7 %) of the 109 clinical NTS and 21 (21.9%) of strains from meat sources had resistance to ≥3 antimicrobial drug classes (MDR). Sixteen (15.7%) of the 102 isolates analyzed by WGS had resistance mechanisms that confer resistance to expanded-spectrum cephalosporins (ESCs), such as ceftriaxone. We identified a bla CTX-M-65 in two S. Infantis isolates from clinical and three S. Infantis isolates from meat sources. These five bla CTX-M-65 -positive S. Infantis strains carried ≥5 additional resistance genes plus a D87Y mutation in gyrA that encodes fluoroquinolone resistance. WGS showed that isolates from patients and meat samples were within ≤10 and ≤5 alleles for S. Infantis and S. Reading, respectively.
Conclusions
A significant proportion of NTS isolates from human and animal sources were MDR and 16% had genetic mechanisms that confer resistant to ceftriaxone. These results emphasize need for integrated surveillance in healthcare and agricultural settings.