Growth of Pseudomonas fluorescens and Pseudomonas fragi in a meat medium as affected by pH (5.8–7.0), water activity (0.97–1.00) and temperature (7–25°C)

A total of 59 strains of Pseudomonas, isolated from meat products, were grown in micro-titer plates in a meat medium over a range of pH (5.8–7.0), aw (0.97–1.00) and temperature (7–25°C). Growths were performed in a meat broth with an automated turbidimeter (Bioscreen C, Labsystem, France). The growth curves obtained in this study did not have sigmoidal shapes making it impossible to calculate growth parameters using the Gompertz equation. The medium was weakly oxygenated in the micro-titer plates and reached 0%-dissolved oxygen at the beginning of the exponential phase. Strains were separated into two groups: P. fragi and P. fluorescens. Strains of P. fragi had shorter lag times than those of P. fluorescens. The impact of such results is interesting in that these could assist to explain the succession of flora that is observed during the processing of meat: P. fluorescens is the dominant bacteria among Pseudomonas spp. at the beginning of a slaughter line and P. fragi becomes dominant during the chilling process.