particle countersfor totalparticleamountsthat can be exploited. Bioaerosol
samples are analysedwithvariousmethods: culturingmethodis the traditional
and widely usedmethodbut it has drawbacks.Otherassaymethodsinclude
microscopy,fluorescence,flowcytometry, ATPbioluminescenceand molecular
methods. For eachenvironmentan appropriatesamplerand assay methodhas to
be chosen.The bioaerosolresults mustalwaysbe interpreted takinginto account
sampling place, sampler, assay method and case-specifics. The future
developmentof real-time continuous monitoringof totalairborne microbes as
wellas specific spoilage contaminants is important, but it will be sometime
before it will be available to the foodindustry.
37.2 Microbialviabilityin the air
Traditionally, microbialviability is understoodas the ability to divideand
multiply. Onlyviable microbes can causeinfection,whileboththe livingand
deadonesor theirproducts can be responsible for allergenicand toxicillnesses.
An airborne organism mayhavea veryshortlife, its stabilitybeing influenced
by relativehumidity (RH),temperature,oxygenlevels, solarand ultraviolet
(UV) radiation, and chemicalfactors (Parrett& Crilly, 2000).A numberof
differentfactors affectingmicrobes can cumulativelystressthemand affecttheir
viability(Griffiths & DeCosemo, 1994).Importantfactors includeorganism
species, cultivationconditions,method and way of aerosolgeneration,sampling
techniquesand the airborne environment.Desiccation,radiation, oxygen,ozone
and its reaction products as wellas various pollutants can affect the viabilityof
microbes (Griffiths& DeCosemo,1994).
The growthphaseaffectsthe survivalof microbesin an aerosol (Griffiths&
DeCosemo, 1994).Brown(1953)foundthat the viability is minimalduring the
transitionfromstationary to logarithmicstages forEscherichia coli. Better
survival ratesfromthe stationaryratherthanfromthe logarithmic stageshave
beenobserved for bothE. coliandSerratia marcescens(Goodlow& Leonard,
1961;Dark& Callow, 1973).There is littleinformationavailableon the survival
of microbes aerosolizedfromfoodenvironments. Sterskyet al.(1972)showed
thatSalmonellaNewBrunswick survivedmuchlonger when aerosolizedfrom
skimmilkthanfromdistilledwater.
Bacillussubtilisvar.nigersporesare widelyreportedto be stablein air. The
viabilitiesofSalmonella entericaserovarenteritidisandSalmonellaenterica
serovartyphimuriumweresignificantlybetterthanthoseshownby aerosolsof
LegionellapneumophilaandMycobacteriumtuberculosisstudiedfor two hours in
air at 24 ÎC with75%RH (McDermid& Lever,1996).Yeastsare eukaryotesand
are likelyto be affecteddifferentlyby aerosolizationand samplingthanbacteria.
Bacterialsporessurvive betterthanvegetativecells.Microbescan mutateand
adaptto changesin theirgrowthenvironment,implyingthat it becomesvery
difficult to knowif a givenstrainwill respondin a consistentway to a stress factor
appliedovera longperiodof time(Griffiths& DeCosemo,1994).
620 Handbookof hygiene controlin the foodindustry