Antibiotic Resistance Patterns of Pseudomonas spp. Isolated From Raw Milk Revealed by Whole Genome Sequencing

Psychrotrophic bacteria in raw milk are most well known for their spoilage potential and the economic losses they cause to the dairy industry. Food-related psychrotrophic bacteria are increasingly reported to have antibiotic resistance features. The aim of this study was to evaluate the resistance patterns ofPseudomonasspp. isolated from bulk-tank milk. In total, we investigated the antibiotic susceptibility profiles of 86Pseudomonasspp. isolates from raw milk. All strains were tested against 15 antimicrobial agents.Pseudomonasisolates were most highly resistant to imipenem (95.3%), followed by trimethoprim-sulfamethoxazole (69.8%), aztreonam (60.5%), chloramphenicol (45.3%), and meropenem (27.9%). Their multiple antibiotic resistance (MAR) index values ranged from 0.0 to 0.8. Whole-genome sequencing revealed the presence of intrinsic resistance determinants, such as BcI,ampC-09,blaCTX-M,oprD,sul1,dfrE,catA1,catB3,catI,floR, andcmlV. Moreover, resistance-nodulation-cell division (RND) and ATP-binding cassette (ABC) antibiotic efflux pumps were also found. This study provides further knowledge of the antibiotic resistance patterns ofPseudomonasspp. in milk, which may advance our understanding of resistance inPseudomonasand suggests that antibiotic resistance ofPseudomonasspp. in raw milk should be a concern.