238 DISINFECTION
to EO produced by dehydration, the cells have
to be actually wetted (Perkins and Lloyd, 1961;
Winge-Heden, 1963; Gilbert et al., 1964).
Alkylating agents act through alkylation of
sulphydryl, amino, carboxyl, hydroxyl and phe-
nolic groupings, with the loss of a hydrogen atom
and the production of an alkyl hydroxyethyl
group (Phillips, 1952, 1958; Kelsey, 1967), and
it seems likely that EO kills microorganisms by
an alkylation of protein molecules (Gilbert et al. ,
1964). The influence of RH on the microbicidal
activity of EO is related to this, since the pres-
ence of insufficient water prevents alkylation,
whereas excess water causes hydrolysis of EO
to ethylene glycol, CH 2 OHCH 2 OH (Wilson and
Bruno, 1950).
5) Effect of drying medium on spore resistance.
Organisms dried from salt solution always show
some survivors after exposure to EO (Royce and
Bowler, 1961; Beeby and Whitehouse, 1965).
Moreover, organisms enclosed within crystals
are protected from the action of EO (Abbott
et al. , 1956; Royce and Bowler, 1961) as a result
of the inability of the gas to penetrate crystalline
materials.
EO has several uses in the pharmaceutical and
medical fields. These include the sterilization
of ophthalmic instruments, anaesthetic equip-
ment, heart-lung machines, disposable syringes
(Rubbo and Gardner, 1968) and hospital blankets
(Kaye, 1950), and as a decontamination proce-
dure for articles handled by tuberculous patients.
There may, however, be a “crazing” of disposable
syringes, and EO treatment is a slow, costly pro-
cess, with a “quarantine” period necessary at the
end of the process to ensure that complete dissipa-
tion of the gas has been achieved.b -Propiolactoneb -Propiolactone (BPL) is a colorless liquid at room tem-
perature. It has been employed as a chemosterilizer in both
the liquid and gaseous states, and is microbicidal in both
forms (Allen and Murphy, 1960). Its antimicrobial activity
depends on its concentration and on the temperature and
RH at which the vapor is used (Spiner and Hoffman, 1960),
a temperature above 24°C being required for optimal activ-
ity. As with EO, RH is of considerable importance in deter-
mining the activity of BPL vapor, although with the latter
a RH in excess of 70% is required for rapid microbicidal
acivity (Hoffman and Warshowsky, 1958). Again, however,
it is not necessarily the atmospheric RH which is of greatest
importance but the location and content of water within the
microbial cell. B. globigii spores equilibrated to 98% are
rapidly killed by BPL at 45% RH, whereas they are more
resistant if preconditioned at 75% RH before treatment
with BPL at 45% RH, and a small proportion of sporesequilibrated at 1% RH are subsequently highly resistant to
BPL at 75% RH (Hoffman, 1968).Bacterial spores are more resistant to BPL than vegeta-
tive cells, viruses or fungi (Lo Grippo et al. , 1955; Trafas
et al. , 1954; Bruch and Koesterer, 1962; Toplin, 1962)
although some strains of Staph. aureas may be almost as
resistant as spores (Hoffman and Warshowsky, 1958).
BPL is also highly active against viruses and rickettsiae
(Hoffman, 1971).
BPL has been used for the chemical sterilization of regen-
erated collagen sutures (Ball et al. , 1961), for the decontamina-
tion of enclosed spaces (Bruch, 1961b) and for the sterilization
of a variety of instruments contaminated with various sporing
and non-sporing bacteria (Allen and Murphy, 1960). However,
its reported carcinogenic effects in rats and mice (Walpole
et al. , 1954) mean that a considerable degree of caution is
needed before BPL is employed as a chemosterilizer.FormaldehydeFormaldehyde vapor may be obtained by evaporating appro-
priate dilutions of standardized batches of commercial for-
malin (a 40% solution of formaldehyde in water) with 10%
methanol added to prevent polymerization (Report, 1958).
Temperature affects the activity of the gas, as does the RH,
there being an increase in activity with increasing RH up to
50%, but little further increase in killing rate as the RH rises
from 50 to 90% (Nordgren, 1939; Report, 1958). In contrast,
gross wetting retards killing.
Bacteria protected by organic matter, such as blood
and sputum are less rapidly killed by formaldehyde vapor
(Nordgren, 1939; Bullock and Rawlins, 1954). Micro-
organisms may also be protected from it when they are
included in a crystal mass, in contrast to surface-contaminated
crystals (Abbot et al. , 1956).
Although bacterial spores are more resistant than vegeta-
tive cells to formaldehyde vapor, the degree of difference
is not high (Phillips, 1952; Report, 1958; Sykes, 1965).
The vapor only has weak penetration, and its application is
thus normally limited to surface sterilization (Borick, 1968;
Davis, 1968). However, the addition of formaldehyde vapor
to steam under sub-atmospheric pressure at temperatures
below 90°C results in deep penetration into fabrics with
destruction of heat-resistant microorganisms (Alder et al. ,
1966; Alder and Simpson, 1982).
Formaldehyde vapor has long been used for the disin-
fection of blankets, and is considered to be one of the best
methods available for disinfecting woolen blankets that have
not received a shrink-resist treatment (International Wool
Secretariat, 1961). It is also used to decontaminate rooms,
buildings and instruments (Hoffman, 1971).CH 2 CH 2OOCC004_002_r03.indd 238C004_002_r03.indd 238 11/18/2005 10:19:30 AM11/18/2005 10:19:30 AM