i.e. foodindustry, hospitalenvironment, etc. However,the number of test
protocolsavailable to evaluate virucidal and mycobactericidalactivity(referto
Section 38.4.3)is limited. In addition,thereis no standardisationand these
protocolstendto varygreatlybetween countries (Maillard,2004)notablywith
the test organisms.In Europe, a virucidaltest for foodhygiene,domesticand
institutionaluse is available(CEN13610),althougha similar protocolfor the
healthcareand veterinaryenvironmenthas not beenpublishedyet (Holah, 2003).
The choiceof the viralindicator is particularly contentious(Maillard,2004).
The number of microorganismsthat shouldbe usedin standardtests has long
beendebatedand differsbetweentest protocols.It is generally acceptedthat the
higher the level of microbial contaminant,the moredifficult the disinfection.
Predictingthe levelof contaminationmight be difficultand oftenthe worstcase
scenario is considered, i.e. a high-inoculum.Mosttests workon the basis of
reducing the number of microorganismsto an acceptablelevel (e.g.a 5 log 10
reduction on surface), but not to the completeelimination(i.e. sterilisation) of
the microorganisms.If this is generally acceptable for mostmicroorganisms,a
problem can arisewithhighlyinfectious or virulent microorganismssuchas the
hepatitis B virus,EscherichiacoliO157for which a completeeliminationwould
be recommendable.
Bacterial phenotype can affectthe activityof antimicrobialbiocides.Growth
conditionsincludingphysical (e.g.temperature,gas)and chemicalconditions
(e.g.pH), nutrient limitationand diet (i.e. excess of lipids), but also whetherthe
cells are grown as a biofilmor in suspension will producemicroorganismswith
a differentphenotype. The metabolic statusof the cell is particularly important
since bacteriawitha `lowmetabolism'or quiescent bacteriaare particularly
resilient to the antimicrobialeffects of biocides (Doddet al., 1997; Holahet al.,
2002; Gilbert et al., 2003). Testing protocols describe meticulously the
preparationof the inoculum,includinggrowthmedium and physicalconditions,
but alsothe numberof passage of the strainsin brothor solidmedia. The
production of the start-upinoculumis discussed furtherin Section38.3.2.38.2.3 Limitations in the use of biocidalproducts
The limitationsin using biocidal products usually referto theirtoxicity,to the
alterationof the surface/equipmentontowhich they are used(e.g.corrosiveness,
colour formation), to theirincompatibility withother components of a formula-
tion,but also to theiroverallefficacyagainst a given predicted microorganism
(Table 38.2). For example, high-level disinfectants are needed for the
disinfectionof critical surfaces in the hospital environment(Rutala and Weber,
1999).Toxicityis also important to consider not onlyfor the end user (e.g.with
antisepsis and preservation)but also for the environment. For example,the use
of highconcentrationsmightnot be acceptable becauseof the hightoxicity for
the environment. Within the foodindustry,considerationmust also be given to
the potential for any biocide residues to taint or otherwise change the
organoleptic propertiesof the foodstuffsproduced.
650 Handbookof hygiene controlin the foodindustry