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

Abstract

The formulation of shelf-stable intermediate-moisture products is a critical food safety issue. Therefore, knowing the precise boundary for the growth-no-growth interface of Staphylococcus aureus is necessary for food safety risk assessment. This study was designed to examine the effects of various humectants and to produce growth boundary models as tools for risk assessment. The molecular mobility and the effects of various physical properties of humectants, such as their glass transition temperatures, their membrane permeability, and their ionic and nonionic properties, on S. aureus growth were investigated. The effects of relative humidity (RH; 84 to 95%, adjusted by sucrose plus fructose, glycerol, or NaCl), initial pH (4.5 to 7.0, adjusted by HCl), and potassium sorbate concentration (0 or 1,000 ppm) on the growth of S. aureus were determined. Growth was monitored by turbidity over a 24-week period. Toxin production was determined by enterotoxin assay. The 1,792 data points generated were analyzed by LIFEREG procedures (SAS Institute, Inc., Cary, N.C.), which showed that all parameters studied significantly affected the growth responses of S. aureus. Differences were observed in the growth-no-growth boundary when different humectants were used to achieve the desired RH values in both the absence and the presence of potassium sorbate. Sucrose plus fructose was most inhibitory at neutral pH values, while NaCl was most inhibitory at low pH values. The addition of potassium sorbate greatly increased the no-growth regions, particularly when pH was <6.0. Published kinetic growth and survival models were compared with boundary models developed in this work. The effects of solutes and differences in modeling approaches are discussed.

nfluences of physicochemical stresses on injury and inactivation behaviour of Listeria innocua

“…When NaCl was used as the solute, L. innocua was more heat resistant. Mazas et al (1999) and Stewart et al (2002) arrived at similar conclusions. Listeria spp.…”

The formation ofStaphylococcus aureusenterotoxin in food environments and advances in risk assessment

“…112,113 Available kinetic tertiary models can be used to predict growth and lag time based on various input values, for example, temperature, pH, water activity, nitrite concentration and aerobic/anaerobic conditions (PMP) (ComBase Predictor) and temperature in various types of meat (THERM). 114 An alternative approach is to describe the boundary between growth and no growth, 95 or survival/death, 115 the time before growth, 116 or the probability of growth, as a function of environmental parameters. Such models can be useful in the design of food processes to prevent growth and enterotoxin production.…”

“…Such models can be useful in the design of food processes to prevent growth and enterotoxin production. For instance, Stewart et al 116 developed a time-togrowth model to study the effects of different humectants used to achieve shelf-stable intermediate-moisture foods. Similarly, Valero et al 95 developed a model for the probability of growth and found an abrupt transition of the interface between growth and no growth at low temperatures, where optimal levels of pH and water activity were required for growth.…”

pH-Wert des Milieus chronischer Wunden

“…Im Sekret chronischer Wunden wird unter nicht permeablen Verbänden ein saureres Wundmilieu gefunden als bei der Verwendung eines permeablen Wundverbandes. In weiterführenden In-vitro-Untersuchungen konnten allerdings keine Unterschiede bezüglich des Bakterienwachstums in den beiden untersuchten Wundsekreten festgestellt werden,sodass hier die Akkumulation von anaerob generierten Stoffwechselprodukten als ein kausaler Faktor diskutiert wurde [24].Die meisten humanpathogenen Keime werden in ihrem Wachstum in einem pHWert Bereich <6,0 und insbesondere zwischen pH 4 und 5 gehemmt, wohingegen deren pH-Optimum mit 6,2-7,8 angegeben wird [14,21,23]. So konnte bei Patienten mit Hemiplegie oder Diabetes mellitus gezeigt werden, dass nach Senkung des pH-Wertes der intakten Haut durch topische Verwendung von sauren Externa die Bakteriendichte deutlich reduziert wird [12].Ein Grund könnte die veränder-te Aktivität,die beispielsweise für Enzyme von Staphylokokken in unterschiedlichen pH-Wert-Bereichen beschrieben wurde sein.So sind die meisten Staphylokokkenenzyme in alkalischen Milieus weniger aktiv, wohingegen in sauren Milieus vermehrt Proteasen ausbildet werden [6].Für das Staphylokokkenenterotoxin C2 (SEC2) konnte aktuell gezeigt werden, dass sich die 3-dimensionale Struktur abhängig vom dem umgebendem pH-Milieu än-dert und somit eine differenzierte Aktivität resultieren könnte [11].Die Modifikation des pH-Wertes im Milieu chronischer Wunden könnte somit über eine gezielte Reduktion der bakteriellen Kolonisation einen relevanten Faktor in der verzöger-ten Abheilung chronischer Wunden beeinflussen.…”