It is the procedure through which all the germs present in the treated material are killed. This procedure can be either physical, such as humid or dry heat and UV radiations, or chemical such as formaldehyde, ethylene oxide, glutaraldehyde, and hydrogen peroxide gas plasma.
The sterilization processes are controlled trough a combination of physical, chemical and biological techniques designed to evaluate the sterilization conditions and the efficiency of the process.
The physical techniques include cycle time control and pressure and temperature indicators control inserted at the equipment’s control board. A correct reading does not ensure a good operation of the cycle, but an incorrect reading could be the first evidence of the existence of a problem.
The chemical techniques (chemical controls) use sensitive substances to one or more sterilization cycle parameters. Usually they indicate the achieved parameters value through a color change. There are chemical controls that sense one parameter and others that respond to multiple sterilization cycle parameters.
The correct performance of a sterilization cycle should be assessed every time a cycle is carried out. In the case of steam processes, it is advisable to include at least three biological indicators per cycle, with a minimal frequency of one control every three cycles. For ethylene oxyde, it is advisable to include at least two biological indicators per cycle. In the case of dry heat, it is recommended to include at least three biological indicators per cycle, with a minimal frequency of one control every three cycles. It is important to notice that every time the processed biological indicators are incubated, an indicator which has not been processed should be included in order to assure that the growing conditions have been favorable enough during the whole sterilization cycle.
It is also worth considering that the more often biological indicators are used in a process, the more reliable will the cycle performance become.
Besides the usual controls, you should include biological indicators whenever:
– A new packaging material is used.
– After training a new staff.
– After a sterilizer has been repaired.
– After any change during the loading process of the sterilizer.
It is always convenient to put the sterilization controls in places that have been previously considered most inaccessible to sterilization agents.
A key place could be the center of the charge, the center of the packaging, or near the equipment door. It is recommendable for each case in particular, to prepare maxim difficulty sterilization dispositives, with the materials that are usually used to pack the material that will be sterilized.
Whenever this happens, it is recommended to check the sterilization process. There are certain variables such as time, temperature, pressure, etc. which might need to be re-adjusted. In case problems continue, the equipment will have to be examined. There might be some inconveniences with the package material before approving its performance.
– Material which has not been thoroughly washed, proteins and precipitated salts may cause the encapsulation of microorganisms, thus avoiding their direct contact with the sterilizing agent and therefore reducing the efficiency on the process.
– Package material which is not appropriate.
– Too much quantity of package material, which can either postpone or completely prevent the entering of the sterilizing agent.
– Overload or wrong loading in the sterilizer.
– Packages placed one above the other where no sterilizing agent can circulate.
– Short period of time for sterilization
– Insufficient temperature
– Concentration of agent too low.
Spores are microscopic biological structures highly resistant to the environmental stress such as drying, temperature, pressure, osmotic stress, chemical agents and radiations. Since they are the most resistant living beings in the whole planet, they are ideal for challenging sterilization processes because, if we can be sure that the spores die, they can confirm the death of any other microorganism present in the idem for sterilization.
It is the period of time required in an order or 90% a population of bacterial spores undergoing a specific sterilization process and under a certain quantity of conditions set up for that process.
TERRAGENE estimates D-values at 121°C, 128°C and 134°C for each lot of BT20 self-conteined Biological Indicator for Steam, and BT50 and BT60 spore strips.
TERRAGENE estimates D-Values at 54°C 60% RH, 600mg/l of EO for each lot of BT10 self-contained biological indicator for EO, and BT40 and BT60 spore strips.
TERRAGENE estimates D-Values at 160°C and 180°C for each lot of semi-self-contained BT30 Biological Indicator for Dry Heat, and BT40 and BT60 spore strips.
Z-Value is definite parameter for temperature sterilization processes. It can be described as the quantity of Celsius grades necessary for varying in an order the D-Value. For instance, for a certain lot, if we have a D-Value at 121°C of 2.0 minutes and the Z-Value for that lot is 10°C, this mean that at 131°C the D-Value will be of 0.2 minutes.
The use of biological indicators minimizes the occurrence of false positives since this is a closed system which does not allow the interchange of microorganisms. However, it allows the interchange of gasses and vapors. Because of their design is not necessary to open a paper packet under sterilization conditions or handle a paper inoculated with spores trying to prevent its contact with non-sterile surfaces and/or air steams which can deposit microorganisms in the spore strips.