cell.Waterhardness is particularly of concern whenthe formulation/product
needsto be dilutedto the appropriatein use concentrationwithon-site water.To
reflectthe use of hardwater, standardtest protocolsrecommendthe use of hard
waterto dilutethe product,and usuallystate its composition (e.g.CEN1276,
1997a;CEN13697, 2001).
Relative humidityaffectsthe activity of gaseous disinfectants (e.g.ethylene
oxide, -propiolactone, formaldehyde).Pre-humidificationand notably the state
of hydration of the microorganismis a determining factorfor theirsensitivityto
antimicrobialprocesses,particularly sterilisation(Russell, 2004).
Factors inherentto the microorganisms
Different types of microorganismspresent differentlevelsof sensitivityto a
given antimicrobial biocide. Attempts have been made to classify micro-
organismsaccording to theiroverallsusceptibility to biocides(Table 38.5).
Usually,suchclassificationrelies uponinformationon the intrinsic property of a
microorganism but is not designed to give a definite answer about the
susceptibilityof a typeof microorganism,since variationwithinspecies and
evenstrainsmightoccur.Practically,the typeof microorganismsexpectedon a
givensurface helpin the selectionof an appropriatedisinfectantor sanitiser.
Antimicrobialtest protocolsusuallyincludetestingagainsta rangeof bacteria
and fungi,whichare selected depending uponthe expected usageof the biocide,
Table38.5 Susceptibilityof microorganismsto biocides
Microorganisms Levelof resistance Comments
Prions High Specialsterilisationprocessescombiningheat
withbiocide.Use of single-useitems
recommended.
Bacterialspores High Sterilisationor high-leveldisinfection.Often
usedas biologicalindicators.
Mycobacteria Highto High-leveldisinfectionrecommended.
intermediate Resistanceto glutaraldehydeand peracetic
acidhas beenreported.
Smallnon- Intermediate Entericvirusesmightbe particularlya
envelopedviruses problemwhenlow-leveldisinfectionis used.
Fungi Intermediate Relativelylittleinformationis availableon the
to low susceptibilityof fungi,and particularlyfungal
spores,to biocides.
VegetativeGram- Intermediate Pseudomonasaeruginosais particularly
negativebacteria to low resilientmicroorganism.
VegetativeGram- Low Generallysensitiveto disinfection.
positivebacteria
Largeenveloped Low The lipidenvelopeis particularlysensitiveto
viruses biocides.
Testingthe effectivenessof disinfectants and sanitisers 649