Purpose: The current study investigated effects of elevated hydrostatic pressure on the cell reduction and inactivation rate of wild-type (WT) and spontaneous rifampicin-resistant (RR) phenotypes of Cronobacter sakazakii.
Methods: Various times (0 to 9 minutes) and intensity levels (0 to 380 MPa) of elevated hydrostatic pressure were investigated for inactivation of a 4-strain mixture of WT and RR Cronobacter sakazakii, inoculated into Tryptic Soy Broth (TSB) and TSB supplemented with rifampicin, respectively. The experiment was conducted at 4ºC, in two biologically independent repetitions, as blocking factors of a randomized complete block design, containing three repetitions per time/pressure/phenotype within each block. Study data was analyzed by the SAS generalized linear model for Tukey- and Dunnett-adjusted ANOVA. The inactivation Kmax, 4D, and D-values were derived from the best-fitted (maximum R2) model obtained by GInaFiT software.
Results: At 380 MPa (0 to 9 minutes), D-values of 1.73 and 1.40, 4D of 6.58 and 5.76, and inactivation Kmax of 1.35±0.2 and 1.61±0.1 were observed for WT and RR phenotypes, respectively. Control counts of 7.54±0.5 and 7.58±0.3 log CFU/mL were reduced (P< 0.05) to 1.90±0.5 and <1.07±0.4 after 9 minutes of treatment at 380 MPa for WT and RR phenotypes, respectively. Treatments shorter than three minutes and below 240 MPa were less efficacious (P≥ 0.05) for reduction of the pathogen in vast majority of the tested intervals.
Significance: This study showed that greater than five-log Cronobacter sakazakii reductions are achievable, as the result of optimized high pressure pasteurization. The WT and RR phenotypes of the pathogen showed comparable sensitivity to pressure and inactivation rates and thus could be used interchangeably in microbiological challenge studies.