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 of Pseudomonas spp. isolated from bulk-tank milk. In total, we investigated the antibiotic susceptibility profiles of 86 Pseudomonas spp. isolates from raw milk. All strains were tested against 15 antimicrobial agents. Pseudomonas isolates 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, and cmlV. Moreover, resistance-nodulationcell division (RND) and ATP-binding cassette (ABC) antibiotic efflux pumps were also found. This study provides further knowledge of the antibiotic resistance patterns of Pseudomonas spp. in milk, which may advance our understanding of resistance in Pseudomonas and suggests that antibiotic resistance of Pseudomonas spp. in raw milk should be a concern.
The objectives of this study were to determine the antimicrobial susceptibility, phylotype, and virulence genes of Escherichia coli (E. coli) from cows with clinical mastitis. A total of 497 mastitis samples were collected and 92 E. coli isolates were identified. E. coli isolates were highly resistance to ampicillin (41.3%), followed by piperacillin (36.9%) and tetracycline (34.7%). Five intimin types, namely μR-ι2, λ, ξR/β2, νR-ε2, η, were observed among 75 EPEC strains with eae gene, with all the intimins were first detected in bovine mastitis milk. And 65 E. coli strains (70.7%) belonged to seven different O serotypes (O121, O91, O22, O26, O128, O111, and O113). For the phylogroup assignment, only 87 E. coli isolates could be assigned into phylogroup B1, A, C, and E. This study suggested the prevailing among EPEC strains isolated from mastitis in five provinces was important to understand the etiology of E. coli.
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