Pseudomonas isolates from raw milk with high level proteolytic activity display reduced carbon substrate utilization and higher levels of antibiotic resistance

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Milk is an ideal food but can be easily contaminated during milking, transportation and storage by Pseudomonas spp. That secrete proteases resulting in milk spoilage. However, genomic features and functional metabolic diversity of Pseudomonas with different protease activity have not been extensively studied. With this aim, the genomic features and functional metabolic diversity of Pseudomonas with differing proteolytic activity were evaluated using whole genome sequencing and metabolomic approaches, respectively as well as, the presence of genes encoding the aprX protease and antibiotic resistance were screened. Pseudomonas strains with higher protease activity possessed more carbohydrate transport and metabolism, signal transduction, secondary metabolite synthesis, polysaccharide lyase and carbohydrate esterase genes. These isolates were more efficient at carbon source utilization and this phenotype was positively related to incubation temperature. The high protease activity group also displayed a multidrug resistance index that was significantly higher than that for the low protease activity group. This is the first report comparing the gene function and metabolic diversity of Pseudomonas with differing levels of proteolytic activity in raw milk.