236 DISINFECTION
will, in fact, destroy the antigenic potency also (Morris and
Darlow, 1971). The inactivation of poliovirus by formalde-
hyde has been considered to be a first-order reaction so that
extrapolation of the death curve would give a point at which
the probability of any infective particles remaining would
approach zero. However, first-order kinetics cannot be used
with any degree of safety to extrapolate the inactivation
curve. Similarly, although the inactivation of SV 40 virus
by formaldehyde has been shown by Sweet and Hilleman
(1960) to be linear, it is now known that this linear inactiva-
tion is followed by a flattening of the curve indicating the
persistence of a residual fraction which resists inactivation.
Formaldehyde is rapidly lethal to vegetative bacteria,
and is sometimes used for this purpose in the preparation of
inactivated bacterial vaccines.MetalsBecause of their antibacterial and antifungal activity, com-
pounds of mercury, silver, copper and tin are of importance
from both medical and industrial points of view (Hugo and
Russell, 1982).
Mercury Compounds These are of two types, the
inorganic mercuric and mercurous salts and the organic
substances. Mercuric salts are primarily bacteriostatic and
fungistatic and contrary to earlier findings are not sporicidal
(see Russell, 1971). Because of their toxicity, the mercuric
salts do not find widespread use in modern medicine, but are
extensively employed as industrial preservatives, e.g., in the
preservation of wood, leather and paper, and in the control
of fungal infections in seeds and bulbs. Mercurous salts have
no application as preservatives.
The most important organic mercury compounds are the
phenylmercuric salts (nitrate, acetate and borate) and thi-
omersal. Phenylmercuric nitrate (PMN) and acetate (PMA)
are now mainly employed as preservatives in various phar-
maceutical and cosmetic products. PMN is also used as a
spermicide in certain contraceptive formulations, as a plant
fungicide and for the disinfection of leather and timber.
However, because of their lack of sporicidal activity at ordi-
nary temperature, the organic mercury compounds cannot be
recommended as sterilizing agents. Some plasmid-containing
gram-negative bacteria are resistant to mercury compounds,
which are vaporized (Chopra, 1982).
Various sulphydryl compounds, such as cysteine and
thioglycollic acid, can reverse mercury-induced bacteriosta-
sis, which led Fildes (1940) to propose that these compounds
combined with, and displaced, mercury from its combina-
tion with the —SH group of an enzyme (E).E EESSSHSHSHSH+ Hg Hg H
2 S+ HgS+Silver Compounds Silver compounds have long been
used in medicine for their antimicrobial activity, which
extends to Gram-positive and Gram-negative bacteria and
fungi. Of the silver compounds available, silver proteinand silver nitrate are the most important. The latter, in the
form of compresses, is highly effective in preventing the
colonization of burns with Ps. aeruginosa and Proteus
species.
Copper Compounds These are bactericidal and fungicidal.
They have been used for the latter purpose for more than 200
years, and their sole use nowadays is as industrial preserva-
tives against fungal spoilage. The most frequently used sub-
stances are copper naphthenate, oxinate, 1-phenylsalicylate
and sulphate; the last-named, in combination with a lime mix-
ture, is known as Bordeaux mixture.
Dialkyldithiocarbamates are considered (Albert, 1963)
to be converted into active bactericides and fungicides in the
presence of copper. Such salts are highly successful, widely
used, agricultural fungicides (Owens, 1969).
Tin Compounds Stannous and stannic salts have little
antimicrobial ctivity. However, when tin is coupled with
organic radicals, forming what are known as the organo-
tins, potent antimicrobial activity results. If R represents the
organic radical linked directly to a tin atom, by C—Sn bond,
and X an inorganic or organic radical not so linked, various
types of compounds can be obtained, of which R—SnN 3 is
most active. Gram-negative bacteria are less sensitive than
Gram-positive bacteria to organotin compounds. Triphenyltin
acetate and hydroxide are important agricultural fungicides.DyesThe acridines have held a valuable place in medicine for sev-
eral years, although with the advent of the antibiotics and
other chemotherapeutic agents, they are now less widely used
than hitherto. The acridines are active against several Gram-
positive and Gram-negative bacteria, and have been used
mainly in treating infected wounds. Their uses and mode of
action have been reviewed (Foster and Russell, 1971).
The most important members of the triphenylmethane
group of dyes are crystal violet, brilliant green and malachite
green. These have mainly been employed for local applica-
tion to burns and wounds.
Some members of a third group of dyes, the quinones,
are important agricultural fungicides. The quinones are
natural dyes which impart color to many forms of plant
and animal life. Chemically, the quinones are diketocy-
clohexadienes, the simplest of which is 1,4-benzoquinone
(Figure 4). Naphtaquinones are the most toxic to bacteria,
moulds and yeasts, followed (in this order) by phenanthren-
equinones, benzoquinones and anthraquinones (Figure 4).
Antimicrobial activity is increased by halogenation, and
two powerful antimicrobial agents employed as fungicides
are chloranil (tetrachloro-1, 4-benzoquinone) and dichlone
(2,3-dichloro-1,4-naphthaquinone).AlcoholsEthyl alcohol, although active against Gram-positive and
Gram-negative bacteria, is devoid of lethal activity against
bacterial spores, and thus cannot be relied upon as a steril-
izing agent (Russell, 1971). Methyl alcohol is likewise notC004_002_r03.indd 236C004_002_r03.indd 236 11/18/2005 10:19:30 AM11/18/2005 10:19:30 AM