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|Language of final thesis:||Slovak|
|Title of the thesis:||Quantitative analysis of environmental factors on Staphylococcus aureus growth|
|Summary:||The effect of water activity values and incubation temperature on the S. aureus 2064 growth dynamic was described in model media. The values of water activity of the tested media were adjusted by sodium chloride, using values from aw = 1.0 up to 0.86. Experiments were carried out at temperatures of 15 to 18 °C in BHI and PCA broth. Based on cultivation experiments the growth curves were obtained and related growth parameters were calculated. On their basis, by use of the mathematical equations, the effect of water activity on the growth dynamics of S. aureus 2064 at observed incubation temperatures was described. The growth intensity was statistically significantly positively related by the decreasing of sodium chloride concentration. Based on obtained results it can be concluded, that during the incubation at 15 °C S. aureus 2064 could withstand additional NaCl concentration of 13 % (aw = 0.893) and 10 % (aw = 0.897) in PCA and BHI broth, in order. At 18 °C and 21 °C the complete reduction of S. aureus 2064 numbers was observed if the NaCl concentration was higher than 15 % (at aw = 0.890 in PCA broth and at aw = 0.871 in BHI broth). At 25 °C the NaCl concentration of 18.17 % was tolerated by S. aureus 2064 and the inhibition was observed at aw higher than 19 % in both tested media. The effect of water activity on the S. aureus 2064 lag-phase duration was described by modified model according to Davey with discrepancy of 20.7 to 32.7 %. Similarly, the growth rate was precisely and reliably described by Gibson model with validation indices of Bf = 0.999 -- 1.001 and Df = 7.6 -22.3 %. The collective effect of water activity and incubation temperature on the S. aureus 2064 growth rate was described by the Ratkowsky square model according to the following equations: sqrt GrPCA = 0.151[(T - Tmin)sqrt(aw -- aw,min)] -- 0.097 (R2PCA = 0.967) for PCA broth and: sqrt GrBHI = 0.143[(T - Tmin)sqrt(aw -- aw,min)] -- 0.085 (R2BHI = 0.885) for BHI broth. Based on validation indices of 25 -- 30 %, the inaccurate prediction are expected in S. aureus growth rates.|
|Key words:||Staphylococcus aureus, predictive microbiology, water activity, temperature|
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