Physicochemical properties of Pseudomonas fragi isolates response to modified atmosphere packaging

Pseudomonas spp., in particular Pseudomonas fragi, are dominant in aerobically stored chilled meats. This work isolated P. fragi isolates from spoiled chicken and investigated the effect of modified atmosphere packaging (MAP, CO2/N2 30%/70%) on physicochemical properties of P. fragi isolates compared to the corresponding controls (air). A total of six P. fragi isolates were isolated from aerobically stored spoiled chicken. MAP inhibited the growth of the isolates primarily in the exponential phase without inducing cell death and weakened the isolate's ability to form biofilms. Isolates 2 and 25, which readily form biofilms, exhibited improved stationary-phase growth in MAP compared to the control packaging. Changes in the surface properties, including reduced motility, increased aggregation and hydrophobicity, were also induced by MAP. The surface property results were then confirmed via scanning electron microscopy. In addition, significant differences were observed in cell phenotypic characterization between individual isolates tested, which indicated that the responses to MAP exposure were strain-dependent. These cell responses allowed P. fragi to adapt to MAP. The study provides practical information regarding microbial responses to MAP stresses, which will help further understanding the bacteriostatic mechanism of MAP.