DISINFECTION 235
same thermodynamic activity will have an equal bactericidal
activity.
Amphoteric compounds, as already stated, are of mixed
anionic-cationic character, and they combine the detergent
properties of anionic compounds with the bacterial proper-
ties of the cationic substances; their bactericidal properties
remain virtually constant over a wide pH range (Barrett, 1969)
and they are less readily inactivated by proteins than are the
QACs (Clegg, 1970). Examples of amphoteric surface-active
agents are dodecyl- b -alanine, dodecyl- b -aminobutyric acid
and dodecyldi(aminoethyl)-glycine (Davis, 1960a,b, 1968), the
last named being a “Tego” compound. The Tego series of com-
pounds have a high molecular weight, and in addition to being
recommended for use in pre-operative hand cleansing and pre-
operative skin preparation it has also been found that they are
suitable for the cleansing of surgical operating theatre floors,
walls and equipment and for ward cleansing (Frisby, 1959,
1961). It has, however, recently been shown that Tego 103S in
1% solution is less active than a 0.5% solution of chlorhexidine
in 70% alcohol (Kuipers and Dankert, 1970). Amphoteric sur-
face-active agents are inactivated by soaps and other anionic
compounds (Frisby, 1959), but they are non-irritating and non-
corrosive. Unfortunately, they tend to be expensive.AldehydesThe two most important aldehydes are glutaraldehyde
(Pentanedial) and formaldehyde (methanal).CH 2 · CHOCH 2 · CHOHO O OHCH 2Hydrated Ring StructureGlutaraldehyde is a dialdehyde which has been used for
several years as a fixative in electron microscopy investigations
and its antimicrobial activity has been comparatively recent
(see Rubbo and Gardner, 1965; Rubbo et al. , 1967; Borick,
1968), but they do indicate that this substance has a valuable
role to play. A 2% solution of glutaraldehyde buffered with
sodium bicarbonate (0.3% w/v is considered to be the optimum
bicarbonate concentration) is effective in killing nonsporing
bacteria within 2 min, M. tuberculosis, fungi and viruses in 10
min, and spores of Bacillus and Clostridium spp. in 3 hours.
Aqueous solutions of glutaraldehyde are acid, and are consider-
ably less active against microorganisms than are alkaline ones
(Pepper and Chandler, 1963; Stonehill et al. , 1963; Snyder and
Cheatle, 1965; Lane et al. , 1966; Rubbo et al. , 1967; Munton
and Russell, 1970a,b), but solutions become progressively less
stable at pHs above 7. Concentrated solutions of glutaraldehyde
(25%) can be purchased, diluted to the required concentration
(2%) and “activated” by the addition of sodium bicarbonate.
(Alternatively, 2% solutions ready for use when “activated”
can also be purchased.) When made alkaline, glutaraldehyde
solutions gradually undergo polymerization with a consequent
loss of activity, this polymerization proceeding rapidly at pHvalues above 9. At pH 7.5–8.5, however, activity is maintained
for at least 2 weeks.
Serum does not affect the antimicrobial activity of glu-
taraldehyde, but the dialdehyde is considerably less active in
nutrient broth at pH 7.5 than it is at the same pH in buffer
(Rubbo et al. , 1967; Munton and Russell, 1970a), the reason
being that glutaraldehyde combines with the peptone present
in broth (which is thereby discolored).
Glutaraldehyde is used as a fixative in the preparation
of microbial cells for electron microscopy. It is a useful
hospital disinfectant, particularly for articles which cannot
be sterilized by physical means (Report, 1965). It has been
employed in the sterilization of cytoscopes in urology (Lane,
McKeever and Fallon, 1966) and of endoscopic instruments,
such as bronchoscopes (Snyder and Cheatle, 1965), as
it has no deleterious effect on the cement or lens coating.
Glutaraldehyde is also employed as a tanning agent in pref-
erence in glyoxal and formaldehyde (Fein et al. , 1959), and
has been shown to inactivate rapidly influenza virus and a
coliphage in mouse tissue blocks (Sabel et al. , 1969).
Glutaraldehyde is non-corrosive, and does not affect
rubber and plastic articles or the sharpness of cutting instru-
ments; because it does not coagulate protein matter, such as
blood and mucus, it does not render the cleaning of blood-
covered instruments more difficult. It is obvious, therefore,
that glutaraldehyde is most useful.
Rubbo et al. (1967) have proposed that the microbicidal
activity of glutaraldehyde is due to the presence of two free
aldehyde groups in the molecule. In solution, glutaraldehyde
exists in an equilibrium between the open chain structure and
the hydrated ring structure (see above), and there is a com-
plete loss of activity if one or both of the aldehyde groups
is altered, whereas a substitution elsewhere in the molecule
reduces, but does not abolish, its activity. It is thus essential
to have free aldehyde groups, which may react with cell sul-
phydryl or amino groups. Glutaraldehyde is about 10 times as
active as glyoxal, with succinaldehyde occupying an interme-
diate position (Pepper and Chandler, 1963). Certain bacteria
treated with glutaraldehyde become pink in color (Munton
and Russell, 1970b) as a result of cell-aldehyde interaction.
Formaldehyde has long been employed as a disinfectant.
Formaldehyde solution is rapidly sporicidal to B. subtilis
(Ortenzio et al. , 1953; cf. Klarmann, 1956, 1959) but not to
various Clostridia (Ortenzio et al. , 1953; Klarmann, 1956,
1959). Ethanol (Rubbo et al. , 1967) and methanol (Willard
and Alexander, 1964) cannot be recommended as vehicles for
formaldehyde, as there is a reduction in antibacterial activity.
Formaldehyde is an important virucidal agent which
finds its greatest use in the preparation of certain sterile vac-
cines, e.g., Poliomyelitis Vaccine (Inactivated). As a result of
the experimental evidence accumulated over several years,
a considerable amount of information is now available on
the kinetics of the virus inactivation by formaldehyde. This
particular vaccine consists of poliovirus Types I, II and III,
and each is inactivated separately and then blended to give
the trivalent vaccine. It is thus essential that formaldehyde
treatment be sufficient to destroy the viruses without affect-
ing their antigenicity; prolonged exposure to the aldehydeC004_002_r03.indd 235C004_002_r03.indd 235 11/18/2005 10:19:30 AM11/18/2005 10:19:30 AM