Spore suspension of Bacillus pumilus was inoculated into universal bottles containing sterile distilled water in water baths at temperatures of 85°C, 90°C and 95°C. At specific time intervals, a sample was removed and spread on nutrient agar plates. The number of colonies formed was used to determine the D-value and z-value. The D-value for 85°C is 64.1 minutes, 25.7 minutes for 90°C and 8.2 minutes for 95°C while the z-value is 11.2°C.
Bacterial endospores are very resistant to hostile chemical and physical environments, thus allowing bacteria to lie dormant for extended periods. A few bacterial genera, such as Bacillus and Clostridium are capable of producing endospores. As these spores are resistant to heat, radiation, desiccation, and disinfectants, they are difficult to eliminate and are a frequent cause of contamination. In addition, endospores do not require nutrients to survive. The impermeability of the spore coat contributes to endospores’ resistance of chemicals. Resistance of heat may be due to the presence of calcium dipicolinate, which stabilize and protects the endospores’ DNA. Water is also removed from the interior of the endospores and the dehydration of the core aids in the resistance to heat and radiation. There are small acid-soluble proteins as well that protect the DNA from heat, drying, radiation and chemicals.
The aim of this experiment was to investigate the effects of temperature on the growth of endospores over time. The decimal reduction value, or D-value that is the time required to reduce numbers by 90% at a particular temperature and the z-value which is a measure of change in the D-value with temperature, were determined from the raw data.
Materials and Methods
The inoculated universal bottles with the spore suspension were incubated in water baths at 85°C, 90°C and 95°C. Linear regression was applied on the data to produce a straight...