CENORIN MEDICAL INFORMATION SERIES The Effect of Air Pockets on the Efficiency of Disinfection of Respiratory Equipment by Pasteurization Performed by: Bio Research Laboratories, Inc. Cenorin, LLC 6324 South 199 th Place Suite 107 Kent, WA 98032 Phone: 253-395-2400 Fax: 253-395-2650 Toll Free: 1-800-426-1042
2 CENORIN MEDICAL INFORMATION SERIES Many potential users of pasteurization equipment have questions about the effect of air pockets on the efficiency of disinfection of respiratory equipment by pasteurization. In this study, we found that air pockets did not compromise the effectiveness of pasteurization in the HLD Systems Models 520 and 540 Pasteurizers. The temperature of the air space and water in the equipment (tubing or bottles) was almost identical after placement in a 160º (70.5º C) bath. This temperature equilibration was complete within 5 minutes. INTRODUCTION Pasteurization has long been reported to be an effective means of disinfecting expensive respiratory therapy equipment in hospitals. It is well known that the pasteurization 1,2 process is capable of destroying the vegetative forms of most bacteria, yeasts, molds and 3 1,2 most animal viruses. In the studies previously cited, vegetative forms of bacteria appear to cause a majority of contamination in respiratory therapy equipment under normal use. The presence of air bubbles within equipment has been suspected as a factor contributing to incomplete disinfection by pasteurization. The effect of air bubbles in equipment during pasteurization has not been thoroughly addressed in the literature. In other pasteurization applications, such as milk pasteurization, literature suggests that air space is 5 F lower than 4 the temperature of the milk. One might expect the same relationship to be true during pasteurization of equipment. In this study, the temperature of air bubbles was monitored to determine correlation of air temperature with bath temperatures and determine the effect of the air bubbles on efficacy of pasteurization. MATERIALS AND METHODS A series of experiments was conducted to determine the effect of air bubbles within a contaminated object or container on temperature and efficacy of disinfection during pasteurization. Containers to be pasteurized were inoculated with five different organisms: Bacillus subtilis (ATCC #6051), Bacillus cereus (ATCC #6464), Escherichia coli (ATCC #25922), Pseudomonas aeruginosa (ATCC #10145) and Staphylococcus aureus (ATCC #29740). The organisms were cultured in brain-heart infusion broth (BHI) at 37 C. Culture dilutions were made using sterile Butterfield s buffered dilution water. Plating to determine initial and final bacterial counts was done by the pour plate method, using Standard Methods Agar (SMA) as the culture medium. Plates were incubated, inverted, for 16-24 hours at 37 C. Pasteurization experiments were performed using the HLD Systems pasteurizer. Separate capped culture tubes, silicon respiratory tubing, or various other jars and bottles were partially filled with BHI containing each type of organism tested, pure cultures or a mixture of all five test organisms. The volume of the 24-hr culture was 10mL. Inoculum was evenly distributed over the entire inner surface of the test container.
3 CENORIN MEDICAL INFORMATION SERIES Additional experiments were conducted in which the inoculum was air-dried on the inner surface of the test container. When inoculum was dried, the test container was inverted in the pasteurizer such that a headspace was maintained through the entire pasteurization cycle. Containers were processed in the pasteurization units at a temperature gauge setting of 168 F for 30 minutes. In each experiment, the actual water temperature was monitored with a calibrated mercury thermometer. The air space temperature was measured in control samples with a Johnstone portable temperature probe with recorder. The temperature probe was not touching glass, tubing, or media. At the end of each pasteurization experiment, text containers were uncapped and aseptically rinsed thoroughly with BHI or Butterfield s buffer. The rinse fluid was transferred to sterile containers, diluted, and plated as previously described. RESULTS Results of air pocket and water temperature monitoring are given in Table 1, below. TABLE 1 Air pocket and water bath temperatures during pasteurization Test I.D. Pasteurizer Type Actual water temp. ( F)* at 30 min. Actual air pocket temp ( F)** at 30 min. Culture tubes, pure cultures HLD Systems Pasteurizer 170 173 Silicon respiratory tubing, pure cultures HLD Systems Pasteurizer 163 168 Quart jars, saliva bottles, Lardahl s; mixed culture HLD Systems Pasteurizer 167 168 Quart jars, mixed culture air-dried in jars HLD Systems Pasteurizer 169 ND ND = Not Determined; Initial temperature gauge setting for pasteurizers is 168 F * Calibrated mercury thermometer ** Johnstone portable probe
4 CENORIN MEDICAL INFORMATION SERIES The outcome of the pasteurization process is assessed by determining the bacterial counts before and after pasteurization. B. cereus was used as a control, given it is a thermophilic spore former. Bacterial counts are summarized in Table 2, below. TABLE 2 Bacterial counts before and after pasteurization Test I.D. Pasteurizer Type Initial bacterial counts (CFU) Bacterial counts after pasteurization (CFU) Culture tubes, pure cultures HLD Systems Pasteurizer Approx. 10 6 each organism B. cereus = 10 4, others = 0 Silicon respiratory tubing, pure cultures HLD Systems Pasteurizer 10 9, except 10 6 B. cereus all = 0 Quart jars, saliva bottles, Lardahl s; mixed culture CFU = Colony Forming Units HLD Systems Pasteurizer up to 10 9, except 10 6 B. cereus all = 0 The rate at which thermal equilibrium occurs between the water bath and the air space was evaluated. Temperature was monitored with an Omega 3-channel temperature probe. Two 30 ml serum vials were utilized, one filled with air and the second with water. Both were sealed with a rubber stopper held in place with an aluminum cap and punctured with a plastic tube. The probe wire was inserted through the plastic and then the plastic tube was withdrawn to seal the probe wire entrance. The temperature probes recorded the following temperatures for each vial when both were submerged in the pasteurized bath at 160 F. TABLE 3 Elapsed Time (minutes) Air Space Temp. ( F) Inside 30 ml Vial Water Temp. ( F) Hg Inside 30 ml: Vial Bath Temp. ( F) Hg Thermometer 0 70 75 160 2.01 145 145 160 4.01 155 155 160 5.00 158 158 160 7.25 160 160 159.5 10.00 161 161 160 15.00 160 161 160 20.00 160 161 160 25.00 160 161 160 30.00 159.5 160 160 Temperature was calibrated using a certified Hg thermometer.
5 CENORIN MEDICAL INFORMATION SERIES DISCUSSIONS & CONCLUSIONS It is important to know if pasteurization systems achieve the proper temperature in trapped air spaces left in medical devices to achieve the high level disinfection that pasteurization assures. In this study, there were no differences in the temperatures achieved between water and air filled devices, such as vessels and containers. The air pockets within the test equipment reached and exceeded the temperature of the surrounding fluid during the pasteurization process, regardless of the instrument used to perform the procedure. All vegetative bacterial cells tested were destroyed by the pasteurization treatment, as was a portion of bacterial spores. These results would normally be observed after pasteurization of contaminated respiratory therapy equipment. Our data indicate air bubbles in the HLD Systems pasteurizers do not compromise the efficiency of pasteurization under the conditions tested. One of the major claims of a rotary type pasteurizer disinfector is that its vertical agitation removes all residual air from respiratory equipment undergoing pasteurization. We were unable to demonstrate that this is the case either with respiratory tubing, quart bottles, Lardahl resuscitation bags or sputum collection bottles. It was also observed that the horizontal agitation of a different type of pasteurizer, when loaded with the same equipment gave better filling (100% vs. 80% for the respiratory tubing). It had similar filling problems with Lardahl resuscitation bags and sputum bottles which have narrow portals and do not fill under water with or without agitation regardless of the machine used or type of agitation. References: 1. Roberts, F.J., Cocxcroft, W.H., and Johnson, H.E. A hot water disinfection method for inhalation therapy equipment. Canad. Med. Ass. J. 101:30 31. 1969. 2. Nelson, E.J. and Ryan K.J. A new use for pasteurization: Disinfection of inhalation therapy equipment. Respiratory Care 16(3):97 103. 1971. 3. Nelson, E.J. Techniques of infection control in respiratory therapy and anesthesia. Techniques Series No. 1:1 4. 19?? 4. Eagan, H.E. Procedures for testing pasteurization equipment. Public Health Service Publication No. 731. 1960. Peformed by: Bio Research Laboratories, Inc. 2897 152nd Ave NE Redmond, WA 98052-4231 425-869-4224 Fax 425-869-4231 By John J. Majnarich, Ph.D. and Wanda Seaman, M.S. July 22, 1996 Cenorin, LLC 6324 South 199 th Place Suite 107 Kent, WA 98032 Phone: 253-395-2400 Fax: 253-395-2650 Toll Free: 1-800-426-1042 CE MISFRM 02 Rev.A Controlled