How can complete sterilization be achieved

Smaller disposable test packs or process challenge devices have been devised to replace the stack of folded surgical towels for testing the efficacy of the vacuum system in a prevacuum sterilizer. Entrapped air will cause a spot to appear on the test sheet, due to the inability of the steam to reach the chemical indicator. If the sterilizer fails the Bowie-Dick test, do not use the sterilizer until it is inspected by the sterilizer maintenance personnel and passes the Bowie-Dick test.

Another design in steam sterilization is a steam flush-pressure pulsing process, which removes air rapidly by repeatedly alternating a steam flush and a pressure pulse above atmospheric pressure. Air is rapidly removed from the load as with the prevacuum sterilizer, but air leaks do not affect this process because the steam in the sterilizing chamber is always above atmospheric pressure.

Like other sterilization systems, the steam cycle is monitored by mechanical, chemical, and biological monitors. Steam sterilizers usually are monitored using a printout or graphically by measuring temperature, the time at the temperature, and pressure. Typically, chemical indicators are affixed to the outside and incorporated into the pack to monitor the temperature or time and temperature. The effectiveness of steam sterilization is monitored with a biological indicator containing spores of Geobacillus stearothermophilus formerly Bacillus stearothermophilus.

Positive spore test results are a relatively rare event and can be attributed to operator error, inadequate steam delivery, or equipment malfunction. Portable table-top steam sterilizers are used in outpatient, dental, and rural clinics. The ability of the sterilizer to reach physical parameters necessary to achieve sterilization should be monitored by mechanical, chemical, and biological indicators.

The oldest and most recognized agent for inactivation of microorganisms is heat. Because a D-value can be determined at various temperatures, a subscript is used to designate the exposure temperature i. D C -values for Geobacillus stearothermophilus used to monitor the steam sterilization process range from 1 to 2 minutes. Heat-resistant nonspore-forming bacteria, yeasts, and fungi have such low D C values that they cannot be experimentally measured.

Moist heat destroys microorganisms by the irreversible coagulation and denaturation of enzymes and structural proteins. In the case of Prions the temperature and time requirements for deactivation are much higher. Steam molecules condense on cooler microorganisms, and transfer joules per gram of steam, very efficiently heating the microorganisms to the temperature at which they are destroyed.

Other methods of heating suffer from the much lower heat transfer of hot dry gases and boundary layer effects, which can insulate and protect the microorganisms.

For maximum effect the Steam must be saturated, and this condition, and the temperature and pressure of the steam are easily monitored, facilitating proof that sterilization has occurred.

By employing Steam Sterilization techniques a high level of sterility can be achieved and the most popular piece of equipment used in laboratories and hospitals is the steam sterilizer or autoclave. Other factors that are associated with sterilization are: 1 Number of organisms on the material and their resistance to the sterilizing agent; 2 Protection afforded organisms by extraneous matter — direct steam must establish direct contact on all surfaces; 3 Exponential death rate.

The numbers of organism dying per unit of time are proportional to numbers present at start to time interval; 4 Functional efficiency of sterilizer and reliability of mechanical components; 5 Human error in operation of equipment. Integrated factors on standardizing sterilization are: 1 Proper preliminary cleaning, assembling, and packaging of supplies to insure direct steam contact; 2 Proper loading of the sterilizer; 3 Approved sterilizer with demonstrated reliability; 4 Adequate exposure period that will provide for complete penetration of the load with a liberal margin of error.

All sterilizers should have time-temperature recorders to provide evidence of adequate exposure for each load. Evidence that a sterilizing temperature has been held for an adequate time, however, does not insure sterilization. This is because the temperature is measured at the outlet valve. Therefore, it does not indicate whether adequate sterilization occurred within dense volumes of liquid or large, dense, fabric-wrapped packs.

Residual air or super heating may also result in incomplete sterilization. The use of chemical monitors, i. However, such monitors do not show whether there was adequate exposure.

The best means of insuring sterility is to use a biologic spore monitor. Microorganisms chosen for spore strips are more resistant to sterilization than are most naturally occurring contaminants. The test organisms are in high concentrations to insure a margin of safety. The spores will be in either impregnated filter-paper strips or in solution in glass ampules. For steam and hot-air sterilization, the thermophile, Bacillus sterathermophilus, is used.

Bacillis globigii is used for ethylene oxide. Most spore strip preparations are provided in envelops that contain one or two strips and a control strip. The test strips are packaged in separate envelopes that are removed and sterilized at the time other material is processed. Subsequently, the test strips and control strips are cultured by placing the strips in a tube of tryptic-digest, casein-soy broth.

These are incubated at 37 oC for gas sterilization and 56 oC for steam sterilization. Other types of spore preparations are commercially available.

The manufacturer's directions should be followed closely. Steam and hot air sterilizers should be tested once a week. Every load of material sterilized with ethylene oxide that is to be placed in contact with deep tissues should be tested. Place the test strips in the center of the test specimen. Never place the strips on an open shelf in the autoclave. Place an ampoule containing a spore solution in the largest vessel to test fluid sterilization.

Handling the spore strips in the laboratory requires considerable care to prevent secondary contamination. Make the transfer with sterile forceps and scissors. Take care not to cross-contaminate the sterilized spore strips with the control strip.

Perform gram staining and sub culturing to prevent false-positive reports that could result from secondary contamination of these cultures. Whenever positive results are obtained, retest the sterilizers immediately with careful examination of thermometer and pressure-gauge readings as well as review of recent time and temperature records.

If any deficiency is observed, or if the repeated sterility test still results in growth, engineering personnel should be consulted promptly. Main navigation MU Alert.