The Effect of Air Pockets on the Efficiency of Disinfection of Respiratory Equipment by Pasteurization

CENORIN MEDICAL INFORMATION SERIES
The E?ect of Air Pockets on the E?ciency of Disinfection
of Respiratory Equipment by Pasteurization
Performed by: Bio Research Laboratories, Inc.
Cenorin, LLC • 6324 South 199th Place • Suite 107 • Kent, WA 98032
Phone: 253-395-2400 • Fax: 253-395-2650 • Tol Free: 1-800-426-1042

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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 expen-
sive respiratory therapy equipment in hospitals.
1,2 It is well known that the pasteurization
process is capable of destroying the vegetative forms of most bacteria, yeasts, molds and
most animal viruses. 3 In the studies previously cited,
1,2 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
the temperature of the milk. 4 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 pasteuri-
zation. 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.

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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. Con-
tainers 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 mer-
cury 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 asepti-
cally 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







Actual air


Actual water
pocket temp


temp. (°F)*
(°F)**
Test I.D.
Pasteurizer Type
at 30 min.
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

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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






Initial bacterial
Bacterial counts after
Test I.D.
Pasteurizer Type
counts (CFU)
pasteurization (CFU)
Culture tubes, pure cultures
HLD Systems Pasteurizer
Approx. 106 each organism
B. cereus = 104, others = 0
Silicon respiratory tubing, pure
cultures
HLD Systems Pasteurizer
109, except 106 B. cereus
al = 0
Quart jars, saliva bot les,
Lardahl’s; mixed culture
HLD Systems Pasteurizer
up to 109, except 106
al = 0
B. cereus
CFU = Colony Forming Units


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

Air Space
Water Temp. (°F)

Elapsed Time
Temp. (°F) Inside
Hg Inside
Bath Temp. (°F)
(minutes)
30 mL Vial
30 mL: Vial
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.

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5 • CENORIN MEDICAL INFORMATION SERIES
DISCUSSIONS & CONCLUSIONS
It is important to know if pasteurization systems achieve the proper tempera-
ture in trapped air spaces left in medical devices to achieve the high level
disinfection that pasteurization assures. In this study, there were no differ-
ences 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 tem-
perature 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 respi-
ratory 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 inha-
lation 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 Publica-
tion 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 199th Place • Suite 107 • Kent, WA 98032
Phone: 253-395-2400 • Fax: 253-395-2650 • Tol Free: 1-800-426-1042
CE MISFRM 02 Rev.A
Controlled

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