RESPONSE SURFACE MODELS FOR THE EFFECTS OF TEMPERATURE, pH, SODIUM CHLORIDE, AND SODIUM NITRITE ON THE AEROBIC AND ANAEROBIC GROWTH OF STAPHYLOCOCCUS AUREUS 196E¹

Abstract

The effects and interactions of temperature (12–45C), initial pH (4.5–9.0), NaCl (0.5–16.5%), and sodium nitrite (1–200 μg/ml) on the aerobic and anaerobic growth of Staphylococcus aureus 196E were studied using 50 ml portions of Brain Heart Infusion Broth in 250ml unsealed and sealed trypsinizing flasks, respectively. The flasks were inoculated to a level of approximately 103 cfu/ml, incubated on a rotary shaker, sampled periodically, and enumerated on Tryptic Soy Agar. Growth curves were generated by fitting the data to the Gompertz function using nonlinear regression analysis. The general growth characteristics of S. aureus in response to the five environmental variables were similar to those observed by other investigators including (1) enhanced growth in the presence of oxygen, (3) ability to grow at high sodium chloride concentrations, and (3) dependence of the bacteriostatic activity of sodium nitrite on pH and oxygen availability. Supplemental studies indicated that growth kinetics were independent of inoculum size, which allowed the Gompertz A term to be treated as a constant. However, the maximum population density (MPD) achieved by the cultures was dependent on the independent variables, requiring that it be modeled in addition to the Gompertz B and M terms. The MPD was then used to calculate the Gompertz C term. Quadratic and cubic response surface models were generated using various data transformations. Quadratic models using and LN‐transformation provided reasonable predictions of the effects of the four variables on the growth kinetics of S. aureus, and should prove useful for providing initial estimates of the behavior of S. aureus in foods.

Dynamics of staphylococcal enterotoxin production in model experiments simulating the fresh cheese environment

“…Figs 1a-c, 2a-c show the growth curve generated using the Pathogen Modelling Program (PMP) online (USDA-ARS, USA) for S. aureus cultured aerobically at 15 °C, pH of 5.5, 2.1% NaCl, and baseline bacterial count of 10 3 cfu·ml -1 . This program is based on experimental results obtained in culture media such as Brain Heart Infusion Broth (Buchanan et al 1993) and should predict the characteristics of bacterial growth in food. Several kinetic predictive growth models of S. aureus can be found in related literature (Sutherland et al 1994;Zurera-Cosano et al 2004).…”

Staphylococcus aureusGrowth Boundaries: Moving towards Mechanistic Predictive Models Based on Solute-Specific Effects

“…The plates were placed on a rack in a sealed plastic container that contained the appropriate saturated salt slurries needed to maintain the environmental RH and thereby ensure the stability of the RHs of the media. The saturated salt solutions used were as follows: ZnSO 4 · H 2 O (83% RH at 37°C), KNO (89% RH at 37°C), KPO 4 (93% RH at 37°C), and K 2 Cr 2 O 7 (96% RH at 37°C). The containers were closed and incubated at 37°C.…”

“…This work resulted in suites of models which are currently available. NaCl was the humectant chosen to control the RH in these models, and the resulting kinetic models do not allow the growth-no-growth boundary to be estimated (4,23,41,47).…”

Estimation of Staphylococcus aureus Growth Parameters from Turbidity Data: Characterization of Strain Variation and Comparison of Methods

“…The PMP model is based on data for a single strain, S. aureus 196E, and NaCl, a non-glass-forming ionic compound, was used as the only humectant (7). In contrast, the present study also used glycerol, a nonionic glass former, as the humectant.…”