Sporicidal Activity of Glutaraldehyde
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Transcript of Sporicidal Activity of Glutaraldehyde
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Journal of Hospital Infection (1980) 1, 63-75
Sporicidal activity of glutaraldehydes and
hypochlorites and other factors influencing their
selection for the treatment of medical equipment
J. R. Babb, C. R. Bradley and G. A. J. Ayliffe
Hospital Infection Research Laboratory, Dudley Road Hospital,
Birmingham B18 7QH
Summary: Nine glutaraldehyde and 4 hypochlorite solutions were tested
for activity against approximately 10’ spores of B. subtilis var. globigii in
suspension or dried on aluminium foil. All glutaraldehydes were effective
against the spores in suspensions in 3 h or less, but the acid glutaraldehydes
were much less effective than alkaline, particularly against the dried spores.
Although the acid glutaraldehyde preparations were more stable, they also
tended to be more corrosive. The buffered hypochlorite solutions were
highly effective, killing the spores in less than 10 mix-r, but have the dis-
advantages of lack of stability and inactivation by organic matter. The
buffered hypochlorites were relatively non-corrosive to metals, but damaged
rubber and the polyurethane coat of an endoscope after prolonged exposure.
All glutaraldehyde preparations passed the Kelsey-Sykes capacity test
with and without yeast and using Pseudomonas aeruginosa as the test organism.
The hypochlorites failed the test when yeast was added.
Introduction
Glutaraldehyde is commonly used for the disinfection or sterilization of heat labile
medical equipment (Ross, 1966; Lowbury, Ayliffe, Geddes & Williams, 1975). In
recent years, particularly following the expiry of the patent on activated alkaline
glutaraldehyde (‘Cidex’), a number of different glutaraldehydes have been intro-
duced. Although most of these preparations contain 2 per cent glutaraldehyde, some
are alkaline and require an activator whilst others are acid and usually do not
require an activator but have the advantage of greater stability. The sporicidal
activity of glutaraldehydes at room temperature tends to be rather slow, especially
when spores are dried onto surfaces, and results with the A.O.A.C. test indicate
that immersion for 10 hours or more is required for sterilization (A.O.A.C. 1975).
A more rapid sporicidal action has been claimed for buffered hypochlorite solutions
(Death & Coates, 1979).
In this study nine solutions of 2 per cent glutaraldehyde and four hypochlorite
preparations were examined for activity against Pseudomonas aeruginosa and spores
of B. subtilis var. globigii. Since these preparations may be used for treating expensive
medical equipment, some tests on corrosion and damage to materials were made.
The relevance of microbiological and corrosion
tests to practical problems of
disinfection and sterilization will also be discussed.
0105~6701/80/010063 + 13 $01.00/O
63
@ 1980 Academic Press Inc. (London) Limited
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64
J. R. Babb et al.
Materials and methods
Preparations of 2 per cent glutaraldehyde
1. ‘Asep’ (Galen Ltd.) pH 7.6, liquid activated, green, stable for 14 days and con-
tains corrosion inhibitor.
2. Acid glutaraldehyde, experimental formulation (not marketed) pH 5.5, stable
no activation required, colourless.
3. ‘Cidex’ CX 250, (Arbrook Products Ltd.) pH 8.6, powder activated, green,
stable for 14 days and contains corrosion inhibitor.
4. ‘Cidex Long Life’ (Arbrook Products Ltd.) pH 7.6, liquid activated, blue,
stable for 28 days, contains corrosion inhibitor, and a surfactant.
5. Alkaline glutaraldehyde, experimental formulation (not marketed) pH 8.6,
powder activated, blue, stable for 14 days, contains a corrosion inhibitor and
surfactant.
6. ‘Clinicide’ (Bioscan) pH 6.2, powder activated, green, stable for 28 days, contains
a corrosion inhibitor and surfactant. (now marketed with an alkaline buffering
system)
7. 3M Instrument Disinfectant (3M UK Ltd.) pH 58, liquid activated, blue,
stable for 28 days, contains a surfactant.
8. ‘Totacide’ (Tenneco Organics Ltd.) pH 7.5, liquid activated, green, stable for
28 days, contains a corrosion inhibitor and a surfactant.
9. ‘Triocide’ (Vann Medical) pH 5.6-6.3, stable, no activation required, colourless,
contains a surfactant
All glutaraldehydes are supplied at ‘in use’ concentrations with the exception of
‘Clinicide’ which is diluted l/10.
Preparations of hypochlorites
1. ‘Anprosol’ (H. W. Andersen Products Ltd.) is a 0.2 per cent sodium hypochlorite
solution containing buffers and surface active ingredients, giving approximately
2000 parts/lo6 of available chlorine, pH 7.5. All the constituents are contained
in a triple compartment pouch which, when cut open, brings the disinfectant,
activators and corrosion inhibitors together. Additionally in each kit are provided
pouches of conditioning agent (detergent, wetting agents and corrosion in-
hibitors) for instrument preparation before immersion in ‘Anprosol.’ The product
is supplied in a marked container suitable for dilution.
2. Sodium hypochlorite solution ‘Sterite’ (Midland Direct Supplies Ltd.) made up
to give 1800 parts/lo6 available chlorine pH approximately 10.0.
3. Buffered sodium hypochlorite solution 250 parts/lo6 available chlorine pH 7.6
(Death & Coates, 1979).
4. Sodium hypochlorite solution ‘Sterite’ made up to give 250 parts/lo6 available
chlorine pH approximately 9.0.
Titration of available chlorine
The ‘available chlorine’ content of hypochlorites was assessed using the arsenite
method (Coates, 1977). 5 ml of hypochlorite was titrated with O-141
N
or 0.0141
N
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Sporicidal activity o f glutaraldehydes and hypochlorites
65
sodium arsenite and the end point detected by a failure to produce a blue stain on
starch iodide paper. The titration in ml, using 0.141 N, gives the available chlorine
concentration directly in g/l (i.e. 1 mEq to 1000 parts/106).
Measurement of pH
pH was measured before each microbiological test with a model 23A pH meter
(Electronic Instruments Ltd). Glutaraldehyde solutions were measured weekly
over a 2%day period.
Miuobiological tests
Kelsey-Sykes capacity test. Tests were carried out as described by Kelsey &
Maurer (1974) for ‘clean’ and ‘dirty’ conditions. Glutaraldehydes and hypo-
chlorites were tested at ‘in use’ concentrations using Ps. aeruginosa NCTC 6749 as
the test organism. Products were tested when freshly prepared, and the glutaralde-
hydes were also tested 14 days after activation.
Sporicidal activity : suspension test
Preparation of spore suspensions. Blood agar plates (Oxoid Columbia agar base
CM 331 + 7.5 per cent horse blood) were seeded with a freshly prepared
culture of Bacillus subtilis var. globigii (NCTC 10073) and incubated for 18 h at
37°C. The resultant growth was removed with sterile cotton wool swabs and a
heavy aq. suspension prepared. The suspension was washed three times in
sterile distilled water, resuspended and heated to 56°C and held for a period of
6 h. Spores were counted, using a surface dropping technique, and stored
overnight at 4°C to enable the spore challenge to be adjusted to approx.
lOr/ml. Sufficient spore suspension was prepared to test all the hypochlorites, and
glutaraldehydes over a 28 day period. Before each test, spores were heated and
counted by the method described.
Test method. 1 ml of spore suspension was added to 10 ml of the freshly prepared
hypochlorite or glutaraldehyde solution in a universal container (previously
rinsed in the disinfectant under test) and thoroughly mixed. 0.02 ml quantities of
this mixture were removed at specific time intervals-2,5, 10, 30 min and 1, 2, 3,4,
5, 6, 7 and 24 h, and added to each of a set of 5 recovery broths and thoroughly
mixed on a ‘rotamixer’. The disinfectant spore mixture was kept at room tempera-
ture (approximately 20°C) throughout the period of the test and recovery broths
were incubated for at least 14 days and examined for growth of the test organism,
i.e. orange pellicle, granular and later turbid suspension. Doubtful tubes were
sub-cultured to confirm the test organism.
The test was repeated with the glutaraldehyde solutions at weekly intervals, i.e.
7, 14, 21 and 28 days after activation. The recovery medium was double strength
nutrient broth (Oxoid No. 2) with the addition of 10 per cent horse serum for the
glutaraldehyde tests and nutrient broth + 0.5 per cent sodium thiosulphate for the
hypochlorite tests.
Tests were carried out to establish that the recovery broth neutralized glutaralde-
hyde carried over during sampling and was not inhibitory to recovered test spores.
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66
J. R. Babb et al.
To confirm the absence of surviving spores in the suspension test Bacillus
subtilis var. globigii spores were added to 10 ml of the freshly prepared disinfectants.
After 3 h the disinfectant/spore suspension mixture was filtered (Millipore
0.45
PM),
the membrane washed with 100 ml of serum nutrient broth and trans-
ferred to a blood agar plate. Membranes were transferred daily to fresh culture
plates for 14 days and examined for colonies of the test organism.
The suspension tests were repeated, with the addition of 2 ml of a 5 per cent
yeast suspension, on three of the glutaraldehydes (‘Asep’, ‘Cidex’ and ‘Totacide’)
showing good sporicidal activity and on the hypochlorites. The yeast, simulating
dirty conditions, was added before the spore suspension.
Sporicidal activity : carrier tests
Bacillus subtilis var. globigii spores (NCTC 10073) 106, deposited onto rolled alumi-
nium foil from a 90 per cent methanol suspension and prepared by the method of
Beeby & Whitehouse (1965), obtained from ‘Steriseal’ Ltd., Redditch, Worcs.,
were used as the test organism and carriers. These spores are marketed as control
organisms for the ethylene oxide sterilization process.
The spore strips were immersed in 10 ml of freshly prepared glutaraldehyde
or hypochlorite, mixed thoroughly on a ‘rotamixer’ for 5 s and left for periods up
to 24 h at room temperature. At the same time intervals as in the suspension tests,
five strips were transferred with sterile wire hooks to each of a series of five recovery
broths. A set of five strips was immersed in a separate universal container for each
time interval.
The strips were shaken in the recovery broths for 5 s on a ‘rotamixer’, incubated
at 37°C and examined for growth for periods up to 14 days. Tests were carried out
on freshly prepared hypochlorites, and glutaraldehydes at 0, 14 and 28 days after
activation. The pH and available chlorine content of the hypochlorites was
measured at the start of each test. Spores were recovered and counted from un-
treated foils by shaking them with glass beads in 10 ml of quarter strength Ringer’s
solution. Tenfold dilutions were made from these washings and plated out onto
the surface of nutrient agar plates using a dropping technique. Colonies were
counted after 24 h incubation at 37°C.
Corrosion tests
Carbon steel and stainless steel scalpel blades were degreased, washed, dried and
immersed in beakers of freshly prepared glutaraldehyde or hypochlorite solutions
for periods up to 3 days. Each blade was placed in a separate container and supported
with nylon thread so that it was partially immersed in each of the disinfectants
under test. Untreated blades and blades immersed in tap water were used for
comparison with the treated blades.
In a second series of tests, various components of ‘Olympus’ flexible fibreoptic
endoscopes, i.e. insertion tube sheath, nylon channels, guide wires, trumpet valves,
berylium/copper and stainless steel protective coils and bending sections, were
immersed either in the 2 per cent glutaraldehyde solutions, 100 immersions for 3 h,
or in the hypochlorites, ‘Anprosol,’ 100 immersions for 2 m in the conditioner
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Sporicidal activity of glutaraldehydes and hypochlorites 67
followed by 15 m in the hypochlorite, or for other hypochlorites 100 immersions of
20 m. Sections of rubber tubing and square pieces of anaesthetic equipment
(reservoir bags) were separately immersed. All items were washed, dried and
examined for signs of damage, e.g. rusting, tarnish, deposition, or loss of elasticity,
after each treatment or on a daily basis.
Glutaraldehydes
Results
All the glutaraldehydes passed the Kelsey & Sykes test at ‘in use’ dilution under
clean and dirty conditions. No growth was obtained in any of the recovery broths.
Tests with added spores showed that adequate neutralization of the disinfectant
had occurred.
Table I. Sporicidal activity
of
2 per cent activated and 2 per cent stable
glutaraldehydes : Suspension test (inoculum l-4-7.4 x 10’ spores of B.
subtilis var. globigii)
Agent
Recom- No. of tubes showing growth after 14 days
mended
incubation
post-
activation Day of
exposure time
life (days) test 10min 30min lh 2h 3h 4h pH
(a) Sporicidal activity of 2 ner cent activated glutaraldehvdes
‘Asep’
‘Cidex’
0
14 :;:
0
14 :;:
Alkaline
glutaraldehyde
‘Cidex Long Life’
‘Clinicide’
‘Totacide’
14 1:
28
0
28 ;;:
0
28 ii
0
28 14
28
‘3M’
28 104
28
315
515
515
515
515
515
515
515
5/5
315
515
515
5/j
515
515
515
515
515
515
515
515
::
515
275
515
575
515
0
00
:
515
275
415
415
00
0
0
5):
575
515
0
i
:
515
0
45:
$5
315
(b) Sporicidal activity of 2 per cent stable glutaraldehydes
Acid glutaraldehyde 15/15
15/15 10/15
‘Triocide’ 15/15
15/15 s/15
: 0
0 0
0 0
575 175
t 0
515 41:
ii 0
0 :
: :
0 0
0 0
: 0
0
0 0
i 0
4115 0
s/15 0
0077:;
0 7.2
i
t:;:
0 7.6
0
:
;:;
7.8
i
5:;
0 7.4
: 2:;
0 6.0
00 77:;
0 7.1
0 5.8
i 5.8.9
0 5.5
0 5.6
Table I(a) shows the sporicidal activity of the activated glutaraldehydes, and I(b)
the stable glutaraldehydes, when the test organism (Bacillus subtilis uar. globigii)
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68
J. R. Babb et al.
was added in suspension. Table I(b) also indicates the pooled results of sporicidal
activity of the stable products on three occasions over a 1 month period. All
products killed 10’ spores within a three hour period, providing the post-activation
period, recommended by the manufacturer, was not exceeded, i.e. 14 or 28 days.
This apparent kill was substantiated by failure of the spores to grow on the surface
of the cultured membrane filter after daily transfers. Many of the products (‘Asep,’
‘Cidex,’ ‘Cidex Long Life,’ ‘
Totacide,’ and ‘Triocide’) killed the spores in less than
1 h.
Table II. Sporicidal activity of 2 per cent glutaraldehydes : Suspension
test with added yeast
No. of tubes showing growth after 14 days incubation
Time of exposure
Agent
‘Asep’
‘Cidex’
‘Totacide’
10 min
515
515
515
30 min lh
515
515
515
515
515
515
2h
3h
575 i
0 0
Spore challenge 3.0 x 10’
The pH of the alkaline formulations (‘Cidex,’ ‘Asep,’ and ‘Totacide’) dropped
over the 2%day test period and this fall appeared to be associated with their
sporicidal activity. The pH of the acid formulations, including the activated acid
products (‘3M’, and ‘Clinicide’), remained constant over the test period although
the sporicidal activity varied considerably. Table II shows the sporicidal activity of
‘Asep,’ ‘Cidex,’ and ‘Totacide’ when organic material (yeast) was present in the
suspension. 10’ spores were killed within 3 h. These three products were chosen
as they did not appear to damage or corrode immersed materials in preliminary
tests and were reasonably effective in the surface spore tests.
The survival of Bacillus subtilis var. globigii dried on rolled aluminium foil and
immersed in the 2 per cent glutaraldehydes is shown in Table III(a), (b). The
differences between the products are more clearly defined than in the suspension
tests and do not appear to be related to the presence of surfactants. The acid
formulations (acid glutaraldehyde and ‘3M’) required 7 or more hours to kill the
spores. All other products killed the spores in under 3 h although the same loss of
activity was noticed with the 14 day products when this period was extended. The
mean number of spores recovered per foil was 1.9 x 10’ (range 8.0 x 10G-
2.3 x 107) which is approximately 1 log higher than stated by the manufacturer.
Hypochlorites
The sporicidal activity of freshly prepared hypochlorites (Table IV suspension
test, Table V surface test), is more rapid than the glutaraldehydes, especially
when buffered to a pH of approximately 7.6. ‘Anprosol’ (1800 parts/lo6 of available
chlorine, pH 7.5) and buffered sodium hypochlorite (pH 7.6, loo-250 parts/l06 of
available chlorine), as described by Death & Coates (1979) killed 10’ spores in under
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p
3
s
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%
a
q
s
u
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z
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0
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70
J. R. Babb et al.
Table IV. Spmicidal activity of hypochlorite solutions : Suspension test
Agent
No. of tubes showing growth after
14 days incubation
Available Time of exposure
chlorine 2
30 1 h 2 h Spore count
(parts 106) min nZn rZn min
w
‘Anprosol’
pH 7-S
Hypochlorite
pH approximately 10
Buffered hypochlorite
pH 7.6
Hypochlorite
pH approximately 9
;;;; w:
215
t : 0 : 5.4.0 x 10’0’
1800 O/S 0 0 8.8 x 106
1800 O/S 0
:
00 : ii 4.4 x lo6
2100 o/5 0 0 0 0 3.1 x 106
1200 s/5 5/s 315 0 0 0 5.4 x 10’
1700 515 515 s/5 415 0 3-o x 10’
1800 515 515 515 5/S 0 : 4.4 x 106
loo s/5 315 415 0 0 4.4 x 106
100 415 0 8 0 0
a0
3.1 x 106
150 o/5 0 0 8-8 x 106
150 o/5 0 0
00
ii
:
5.4 x 10’
250 O/5 0 0 0 0 1.9 x 10’
100 515 515 515 l/5 0 : 3-l x 106
loo s/5 515 515 415 0 4-4 x 106
150 515 s/5 5/s 315 0 5.4 x 10’
150 315 l/5 215 0 0 8-8 x 106
250 s/5 515 515 515 0 0 3.0 x 10’
10 min and often in under 2 min. Unbuffered preparations were less effective, and
times required to kill 10’ spores were comparable with those of the better glutar-
aldehydes.
Table V. Sporidal activity of hypochlorite solutions : Surface test
Agent
Available
No. of tubes showing growth after 14 days
incubation
chlorine
Time of exposure
(parts 103 2min
5 min 10 min 30 min 1 h
‘Anprosol
pH 7.5
Hypochlorite
pH approximately 10
Buffered hypochlorite
pH 7.6
Hypochlorite
pH approximately 9
1800 015 0 0 0 0
1800 515 515 515 0 0
250 015 0 0 0 0
250 515 515 515 315 0
Mean spore count per strip 1.9 x 10’
In the presence of yeast, all hypochlorites failed to kill spores even when the
exposure period was extended to 24 h. These failures were also shown in the
capacity test of Kelsey & Sykes. The activity of the hypochlorites diminishes fairly
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Sporicidal activity of glutaraldehydes and hypochlorites
71
rapidly after preparation, particularly with lower dilutions, as does the available
chlorine concentration, e.g. ‘Anprosol’ showed a fall from 1800 to 1200 parts/l06
in 24 h, and buffered hypochlorites from 250 to 130 parts/lOs.
corrosionests
The alkaline glutaraldehydes ‘Asep, ’ ‘Cidex,’ ‘Cidex Long Life’ and ‘Totacide’ did
not appear to cause damage to carbon steel or stainless steel scalpel blades when
immersed for periods up to 3 days.
‘Triocide’ on the other hand showed some
deterioration of carbon steel (rust and tarnish) after a short period (3 h) of im-
mersion and the stainless steel blade, separately immersed, was rusted within 3
days. Immersion in an acid glutaraldehyde, e.g. ‘Clinicide’ and ‘3M’ also produced
damage to carbon steel blades although there was no damage to stainless steel.
This effect was minimal in 3 h, although considerable at 3 days.
The interpretation of tests on other materials was more difficult. The buffered
alkaline formulations ‘Cidex,’ ‘Cidex Long Life’ and ‘Totacide’ caused no visible
damage to collections of endoscope components after 100 immersions of 3 h. The
acid formulations ‘Clinicide,’
‘
Triocide’ and ‘3M,’ became cloudy and heavy
deposits formed making visual examination of components difficult. Some damage
was certainly caused to collections of dissimilar metals particularly copper alloys.
‘Anprosol’ (pH 7*5),
and buffered hypochlorites (pH 7.6) caused little damage to
immersed scalpel blades and metal endoscope components although non-buffered
hypochlorite, pH 9-10, caused severe corrosion of carbon steel within a few hours.
Two problems were,
however, noticed with the hypochlorites, including the
buffered formulations, especially at higher concentrations. A thick, white deposit
built up on the insertion tube of the ‘Olympus’ flexible fibreoptic endoscopes during
100 immersions and although this could be scraped or wiped off, the polyurethane
coating appeared to be destroyed. Sections of rubber reservoir bags and tubing
were also damaged. The rubber hardened, lost its resilience, and cracks appeared
on the surface when stretched.
Discussion
A reproducible quantitative suspension test measuring the log reduction in numbers
of organisms would have been preferable to the technique used (Reybrouck &
Werner, 1977). However, in view of the large number of tests, this was not possible
and a semi-quantitative method was used to assess sporicidal activity. The results
provide a useful comparison between the agents tested but do not necessarily
indicate exposure times required for sterilization in practice.
Spores vary in their resistance to disinfectants, depending on their method of
preparation, but the spores of B. subtilis var. globigii, as used in these tests, are
likely to be more resistant to glutaraldehydes and hypochlorites than pathogenic
species. The numbers used were also considerably higher than would be found on a
cleaned instrument. The preparation of a reliable spore suspension is often difficult
and the commercial spore strips proved to be consistent in both numbers of spores
and in response to the chemical agents. Glutaraldehyde is not easily neutralized but
dilution in broth containing 10 per cent serum was found to be as reliable as other
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72
J. R. Babb et al.
potential neutralizers and is not toxic to damaged organisms (Russell, Ahonkhai &
Rogers, 1979). Attempts to recover damaged spores using a membrane filter
technique also failed.
All the glutaraldehyde preparations passed the Kelsey-Sykes capacity test, and
killed spores in suspension in 3 h. The alkaline glutaraldehydes were generally
more active than the acid preparations some of which required long periods to kill
spores dried onto metal carriers. The presence of a surfactant did not appear to
improve the effect. Although the A.O.A.C. test suggests a 10 h exposure is neces-
sary to achieve a complete sporicidal effect (A.O.A.C. 1975), 3 h should be sufficient
for practical purposes, particularly as spores are infrequent on clean medical equip-
ment (Spaulding, 1978). Th e immersion, at 20°C of five or more commercial
spore suspensions dried on metal foil could provide a useful laboratory screening
test for glutaraldehydes. This test should be done on activated glutaraldehydes,
stored at 20°C on their expiry date, i.e. at 14 or 28 days after activation.
Opinions on the tuberculocidal activity of 2 per cent glutaraldehyde at room
temperature vary but the immersion times required are considerably shorter than
for spores and 20 m is generally considered adequate (Bergan & Lystad, 1971,
Miner
et al., 1977).
A possible advantage of using acid glutaraldehydes is stability. When heated to
55-60°C their sporicidal activity is greatly enhanced (Sierra & Boucher, 1971),
and in our tests lo6 spores were killed in less than 5 min at this temperature. The
differences between the sporicidal activity of the alkaline and acid glutaraldehydes
diminishes with a corresponding increase in temperature. However, special equip-
ment would be required for this treatment and may have to include equipment for
the removal of toxic vapours. An acid solution of 2 per cent glutaraldehyde (pH
3-4) is stable for several years. However, when alkalinized to produce the optimum
sporicidal activity the corresponding loss in active aldehyde groups, and hence
stability, limits its use to 14 days. By stabilizing the pH to approximately 7.6 the
period of activity of alkaline glutaraldehydes can be extended, with no loss in
sporicidal activity, to 28 days in situations of low dilution (Miner et al., 1977).
This is supported by our findings although the interpretation of these results in the
practical situation should be treated with some caution.
In this study, the acid glutaraldehydes were stable and the activated glutaralde-
hydes showed little loss in activity over 14 days. However, the length of time a
disinfectant is repeatedly used depends on the degree of dilution, the amount of
organic and other materials added to it, and storage conditions as well as its stability.
Although 2 per cent glutaraldehyde is not readily inactivated by organic materials,
repeated use of the same solution over long periods is not good practice. Dis-
infectant solutions should preferably be discarded after each use, but this practice
may be too expensive with glutaraldehyde. If used infrequently and for clean eyuip-
ment only, 7-14 days use would seem to be a useful compromise, but the decision
should be made by the microbiologist depending on the particular use of the
solution.
The interpretation of the corrosion tests presented some problems.’ The acid
formulations usually caused greater damage to immersed metals and as their spori-
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Sporicidal activity of glutaraldehydes and hypochlorites 73
tidal activity is less rapid, longer immersion times may be required. Carbon steel is
rarely incorporated in expensive equipment and corrosion of this alone is of doubtful
practical significance. Nevertheless, it seems reasonable to choose a product which
contains a corrosion inhibitor for disinfection or sterilization of expensive equip-
ment. There is always the possibility of accidental long exposures, e.g. over a week-
end. It is obviously less important when disinfecting inexpensive equipment or
using short exposure times, but it is advisable to carry out in-use tests or to consult
the instrument manufacturer before changing from one preparation to another.
The hypochlorite solutions have several potential advantages. They kill spores
rapidly and instruments could be ‘sterilized’ rather than disinfected between
patients during busy endoscopy sessions. Hypochlorites are cheap and could be
discarded after each use or after an operating session. However, the cost of essential
buffers and corrosion inhibitors is likely to increase considerably this cost. These
solutions have been used for disinfecting infant feeding bottles for many years and
dilute solutions are relatively non-toxic. The main disadvantages of hypochlorites
are inactivation by organic material, instability at low concentration, and possible
damage to instrument components. Two of the buffered preparations examined,
pH 7-S-7.6 (‘Anprosol’ and buffered hypochlorite), showed surprisingly little
damage to metals but did cause some damage to the outer layer of the insertion
tube of an ‘Olympus’ flexible fibre-optic endoscope on prolonged exposure, and to
rubber items, e.g. anaesthetic equipment. We have also received complaints that
endoscope eye piece mounts are likely to bleach during prolonged or frequent
immersions in hypochlorite and that surfactants and conditioning agents, used
prior to or during disinfection, remove essential lubricants and these should be
replaced. It could be argued that only short exposures are required, but accidental
immersion for long periods is always possible particularly if staff are familiarised
with the use of glutaraldehydes. However, if the risk is known, users tend to be
more careful, e.g. alcoholic solutions of chlorhexidine are sometimes used for
disinfection of cystoscopes, and exposure for longer than a few minutes may damage
the lens mounting.
Heat is the most reliable method of disinfection or sterilization, and the use of
chemical solutions of disinfectants or ‘sterilants’ should rarely be required in
hospitals, but autoclaving at high temperature will damage most endoscopes and
destroy flexible fibrescopes. Low temperature steam at 73°C for 10 min is perhaps
the most suitable method for disinfecting cystoscopes between patients, and low
temperature steam with formaldehyde for longer periods for sterilizing laparoscopes
and arthroscopes (Alder, Gingell & Mitchell, 1971). Low temperature steam is also
particularly suitable for the disinfection of respiratory equipment, where hypo-
chlorites cannot be used as rubber is damaged, and inadequate removal of glutar-
aldehyde is always a potential hazard to the patient. However, low temperature
steam machines are not always available and reliable low temperature steam and
formaldehyde machines are still being developed (Cripps, Deverill & Ayliffe, 1976).
Low temperature steam, especially with formaldehyde, will damage most of the
flexible fibre-optic endoscopes in use at the present time. Chemical disinfection is
therefore required and 2 per cent glutaraldehyde is commonly used despite the
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74 J. R. Babb et al.
problems of penetration of narrow tubing and valves and the necessity of thorough
rinsing. Treatment of flexible fibre-optic endoscopes with glutaraldehyde for a
short period, between use on different patients, is a useful compromise (Axon,
Phillips, Cotton & Avery, 1974; Ayliffe & Deverill, 1979; Noy, Harrison, Holmes
& Cockel, 1980). Cleaning according to the manufacturers instructions is more
effective, but takes up to 20 min. Although exposure to glutaraldehydes for 30-
60 min should be adequate following use of an endoscope in a patient with tubercu-
losis, hepatitis or salmonellosis, treatment of the cleaned instrument with ethylene
oxide will further increase the margin of safety.
Treatment with glutaraldehyde for lo-20 min will disinfect but not sterilize, yet
laparoscopes and arthroscopes are often treated for this short time. Despite
inadequate sterilization infection appears to be rare, presumably because there are
few potentially pathogenic spores on the cleaned endoscope. The use of hypo-
chlorites could considerably increase the reliability of this procedure and further
studies are in progress. Endoscopes are expensive, and often complex, and are
difficult to clean, disinfect, or sterilize. It is hoped that manufacturers will produce
instruments that will withstand autoclaving at high temperatures without short-
ening the life of the instrument.
We wish to thank ‘KeyMed’ for supplying the ‘Olympus’ endoscope components used
for disinfectant immersion studies and the disinfectant manufacturers for the products
tested.
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