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|Language of final thesis:||Slovak|
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|Title of the thesis:||Termoresistance of Staphylococcus aureus|
|Summary:||In the diploma thesis, I focused on the thermoresistance of the Staphylococcus aureus affeced by alternating of enviromental conditions. In an effort to ensure hygienic and sanitary harmlessness of slovak steamed cheeses, the aim of the thesis was to quantify the character of S. aureus 2064 inhibition in the model PCA broth and in UHT milk at temperatures of 51, 53, 55, 57, 61 and 63 °C, then also in PCA broth with changing of aw values (0.99; 0.97; 0.95; 0.93; 0.91; 0.89 and 0.86), pH (6.0; 5.5; 5.0; 4.5 and 4.0) and their combinations and to set specific D- and z-values. Based on experiments, it can be concluded that thermoresistance of isolate 2064 naturally decreased with the simultaneous increase of the incubation temperature in the PCA broth and in UHT milk. In PCA broth the D-values were in the range from 7.65 to 99.00 minutes and a corresponding z-value was 10.83 °C while in milk the D-values increased to 21.30 – 123.00 minutes in the temperature range of 51 – 63 °C and z-value reached 20.00 °C. Based on experiments in capillaries, I found out that the volume of the medium did not have a statistically significant effect (α > 0.05) on the thermoresistance. Due to the reduced aw values, I noted that at all observed temperatures (51, 55, 61 and 63 °C) there was an increase in the thermoresistance of isolate 2064. Compared to the D-values in PCA broth without salt addition, the D-values rose to 122.4 – 232.8 minutes at 51 °C and at 55 °C D-values rose to 114.00 – 300.30 minutes. At higher temperatures 61 and 63 °C, D-values dropped to 39.00 – 62.25 minutes and 15.80 – 63.80 minutes, respectively. On the contrary, a more negative effect on thermoresistance by decreasing of pH value was noticed. The calculated D-values reached 24.00 – 117.00 minutes at 51 °C, 36.45 – 72.00 minutes at 55 °C and at higher temperatures 61 and 63 °C D-values were 2.55 – 23.25 minutes and 2.25 – 13.20 minutes, respectively. During the devitalisation of isolate 2064 with simultaneous reduction of aw value (0.99 and 0.97) and pH value (in the range 5.5 – 4.5), z-values varied in the interval from 7.06 to 13.93 °C. The most intensive inhibition of isolate 2064 occured at 5 % of salt addition and with decreasing of pH value to values of 5.0 to 4.5, naturally at 63 °C, and D-values in this case reached values in the range of 3 to 10 minutes.|
|Key words:||Staphylococcus aureus, thermoresistance, z-value, D-value|
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