High spoilage potential and multidrug resistance of P. aeruginosa strains isolated from sheep milk

The aim of this study was to evaluate the lipoproteolytic spoilage potential and the antimicrobial resistance profile of P. aeruginosa strains isolated from refrigerated raw sheep milk. After keeping the collected samples at 9 °C for 72 h, they were plated on Pseudomonas Agar Base with Cetrimide, Fucidin, Cephalothin (25 °C/48 h). The genus Pseudomonas spp., the species P. aeruginosa and the presence of the aprX gene were confirmed by polymerase chain reaction. The spoilage capacity (presence or absence) and potential (size of lipolysis and/or proteolysis halos on agar) were performed using Milk Agar and Tributyrin Agar Base (21 °C/72 h). Antimicrobial susceptibility was determined using the disc diffusion method (35 °C/18 h). A total of 178 strains of Pseudomonas spp. were isolated, of which 13 % (23) were P. aeruginosa. Of these, 96.65 % expressed lipoproteolytic capacity, which points to a possible problem in the quality of dairy products. In terms of spoilage potential, proteolytic activity was predominant. All P. aeruginosa strains carried the aprX gene. P. aeruginosa were susceptible to piperacillin-tazobactam (100 %), gentamicin (100 %), amikacin (100 %), ciprofloxacin (100 %), imipenem (91.3 %), levoflaxacin (86.9 %), trimethoprim (86.9 %), tetracycline (82.6 %), chloramphenicol (52.1 %). The isolated strains were resistant to ampicillin (95.6 %), erythromycin (95.6 %), ceftazidine (78.2 %) and aztreonam (47.82 %). In addition, 19 P. aeruginosa strains showed multidrug resistance. These results highlight the importance of P. aeruginosa control in the sheep dairy industry, as these microorganisms exhibit high spoilage potential with proteolytic predominance and multidrug resistance, which are important public health issues.