Cardinal parameter meta-regression models describing listeria monocytogenes growth in broth

Introduction: Since Listeria monocytogenes is one of the most virulent foodborne pathogens, substantial research has been devoted to estimate its growth rate (GR) under different conditions of temperature, pH and water activity (aw). Purpose: Thus, this study’s objective was to extract all published findings on L. monocytogenes growth in broth, and unify them by constructing meta-regression models based on cardinal [temperature], [temperature][pH] and [temperature][pH][aw] secondary models. Methods: Suitable primary studies were identified through an exhaustive literature search. From each of the 49 studies considered appropriate for inclusion, the following data were extracted: GR, temperature, pH, aw, type of broth, reading type (CFU or optical density) and inoculum concentration. The meta-analytical dataset comprised 2009 GR measures. Weights were assigned to studies according to the number of time points sampled to calculate GR. Results: The cardinal [temperature][pH] meta-regression suggested that higher inoculum levels (2.0 to 6.5 log CFU/g) tend to produce lower estimates (P<.0001) of Tmax, Topt, pHmax and pHopt, although it does not seem to affect (P=0.909) the optimum GR (μopt). The cardinal [temperature] meta-regression demonstrated that reading type was not as important a source of between-study variability (R2=1.0 to 7.5%) as type of broth, which was responsible for 25 to 70% of the heterogeneity (τ²=11.22). Thus, the most parsimonious cardinal [temperature][pH][aw] meta-regression model was built upon a nested random-effects structure of studies within type of broth, which produced the following cardinal estimates: Tmin=-1.273°C (SE=0.178), Topt=37.24°C (SE=0.789), Tmax=45.12°C (SE=0.013), pHmin=4.298 (SE=0.005), pHopt=7.090 (SE=0.073), pHmax=9.510 (SE=0.117), aw min=0.829 (SE=0.005) and aw opt=0.995 (SE=0.001). The μopt was affected by reading type (R2=15%), being higher for OD (1.324 log/h; SE=0.100) than for CFU (0.967 log/h; SE=0.094). Significance: By integrating the outcomes from numerous L. mono- cytogenes growth experiments, the cardinal parameters for temperature, pH and aw obtained through meta-analysis represent very accurate estimates that can be used as reference values.