P630
“Pathogens include many common species of bacteria and viruses. Bacteria which are known to cause disease in humans are usually able to grow very well near human body temperature (37 °C) and moist conditions. Factors that affect the growth of these bacteria on surfaces include temperature, oxygen availability, and pH.
In the medical industry, the sterilization of equipment and foods that will be presented to patients is a necessity, and is the sterilization can proceed through the use of increased temperature. In the table below, the K value is the length of time at which the bacteria needs to be held at temperature °C in order for 90% of the bacteria to be eliminated. Typically, to remove 99% of the bacteria, the K value needs to be doubled at the same Z value. The doubling time refers to the length of time for the population of bacteria to double, given ideal growing conditions.
Essentially,
Where (1 – 0.9)n represents the proportion of remaining bacteria, and n is the number of heating cycles.
| Bacterium | Inoculum Needed | Doubling Time (min) | K (min) | Z (°C) |
| S. aureus | 2 x 104 | 140 | 8.5 | 55 |
| V. cholerae | 1.8 x 103 | 42 | 3 | 40 |
| E. coli | 2.5 x 103 | 20 | 15 | 62 |
| L. monocytogenes | 200-500 | 60 | 2.8 | 53 |
| C. botulinum | 25-50 | 54 | 10 | 85 |
Depending on the initial concentration of bacteria, it can be necessary to heat the equipment or food for many cycles before sterilization criteria or met. For example, although V. cholerae requires an inoculum of 103 bacteria to be pathogenic, species such as C. botulinum may only need 5 – 10 bacteria to establish an infection. ”
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