240 DISINFECTION
The disinfection of fermentation laboratories has been
described by Darlow (1969). Gaseous disinfectants may be
employed, and aerosols appear to have an important role to
play. Local disinfection of bench tops, floors, etc. is also a
standard practice. The importance of disinfectants in water
conservation is emphasized by Fielden (1969), and in the
pharmaceutical industry by Underwood (1980).
The control of airborne microorganisms is of particu-
lar importance in the fermentation industry, in laboratories
where strict asepsis is essential (e.g., in the production of
various sterile products in the pharmaceutical industry and
in hospital pharmacy departments, as well as in the rearing
of germ-free animals), in hospital wards to reduce the inci-
dence of cross-infection, and in special wards set aside for
patients with a rare disease (hypogammaglobulinaemia) who
are particularly sensitive to infection.
This control is normally achieved by the use of special
air filters, often in conjunction with ultraviolet lamps to
irradiate the upper atmosphere. Disinfectants in the form
of aerosols are also of importance in aerial disinfection. To
be effective for air disinfection, a chemical should ideally
possess the following properties:1) be odorless, cheap and stable
2) be without toxic or irritant properties
3) be capable of being dispersed in the air, with con-
sequent complete and rapid mixing of infected air
and chemical
4) be capable of maintaining an effective concentra-
tion in the air
5) be highly and rapidly effective against airborne
organisms
6) be unaffected by relative humidity (RH).Aerosols consist of a very fine dispersed liquid phase
in a gaseous (air) continuous phase. The germicide must
be nebulized in sufficiently fine spray (aerosols droplets
of <1 μ m are the accepted standard) so that it will remain
airborne and thus have ample opportunity to collide with
any microorganisms present in the air. At low RH, particles
are too dry for adequate condensation of the disinfectant
that such organisms enclosed in particles, and thus bacteria
occurring on dust or on surfaces are much less susceptible
to the aerial disinfectant than such organisms enclosed
in droplets (Sykes, 1965). The optimum RH is usually c.
40–60%.
Chemical aerosols are often generated in the following
manner: if the chemical is liquid, it may be sprayed directly
into the air from an atomizer; if the chemical exists as a
solid, it may be dissolved in an appropriate solvent, e.g.,
propylene glycol, and atomized, or alternatively the solid
may be vaporized by heat from a thermostatically-con-
trolled hot-plate.
Chemicals which have been used as aerial disinfectants
include hexylresorcinol, lactic acid, propylene glycol (this
possesses antimicrobial activity in its own right), hypo-
chlorous acid, formaldehyde gas and sulphur dioxide.Other Uses of Antimicrobial AgentsAntimicrobial agents are widely employed as preservatives
in pharmaceutical and cosmetic products. Factors influenc-
ing their activity, as well as those governing their choice in
different classes of sterile or non-sterile products have been
well considered by Bean (1972), Croshaw (1977), Parker
(1978, 1982), Kazmi and Mitchell (1978a,b), Allwood
(1980) and Beveridge (1980).
Preservation is also required in other specialized areas,
e.g., in cutting oils (Hill, 1982a), fuels (Hill, 1982b), paper and
pulp (Weir, 1982), wood (Richardson, 1982), paint (Springle
and Briggs, 1982) and textiles (Hugo, 1982b) and in the con-
struction industry (Bravery, 1982). A most important aspect
concerns the use of chemical food preservatives and this has
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