Attenuation of MicororganismsAttenuation of MicororganismsCharles P. GerbaCharles P. Gerba

Department of Soil, Water and Environmental Department of Soil, Water and Environmental ScienceScience

AndAndDepartment of Epidemiology and Department of Epidemiology and

BiosatisticsBiosatisticsUniversity of ArizonaUniversity of Arizona

Microbial Die-off /Decay/Inactivation Microbial Die-off /Decay/Inactivation (Viruses)/Loss of Infectivity(Viruses)/Loss of Infectivity

Viruses and protozoan parasites can not Viruses and protozoan parasites can not replicate outside of the hostreplicate outside of the host

Under some environmental conditions Under some environmental conditions bacterial pathogens (borne i.e waterborne) bacterial pathogens (borne i.e waterborne) can replicate (food, sediments, biosolids)can replicate (food, sediments, biosolids)

““based” pathogens naturally occur in the based” pathogens naturally occur in the environment i.e. waterbased (Legionella, environment i.e. waterbased (Legionella, Pseudomonas) and grow in the Pseudomonas) and grow in the environmentenvironment

Microbial Die-off /Decay/Inactivation Microbial Die-off /Decay/Inactivation (Viruses)/Loss of Infectivity(Viruses)/Loss of Infectivity

Virus inactivation occurs by either denaturization Virus inactivation occurs by either denaturization of the protein coat or nucleic acidof the protein coat or nucleic acid

Some viruses contain a lipid coat and its Some viruses contain a lipid coat and its damage (by detergents) will result in its loss of damage (by detergents) will result in its loss of infectivityinfectivity

As a general rule enteric viruses survive longer As a general rule enteric viruses survive longer than respiratory virusesthan respiratory viruses

As a general rule enteric viruses are more As a general rule enteric viruses are more resistant to disinfectants than vegetative resistant to disinfectants than vegetative bacterial cells bacterial cells

Microbial Die-off Microbial Die-off /Decay/Inactivation /Loss of /Decay/Inactivation /Loss of

InfectivityInfectivity Bacteria can enter a non-cultural state in Bacteria can enter a non-cultural state in

the environment or exposure to stressthe environment or exposure to stress Bacterial die-off occurs from damage to Bacterial die-off occurs from damage to

cell wall/membrane/nucleic acid/ enzyme cell wall/membrane/nucleic acid/ enzyme systems. Repair of damage is possible systems. Repair of damage is possible dependent on the degree of damage.dependent on the degree of damage.

Most disinfectant resistant bacteria are Most disinfectant resistant bacteria are mycobacterium and spore formersmycobacterium and spore formers

Factors Controlling the Survival of Factors Controlling the Survival of Enteric Pathogens in WaterEnteric Pathogens in Water

TemperatureTemperature – longer survival at lower – longer survival at lower temperaturestemperatures

pHpH –best survival between pH 7 to 8.0. Viruses –best survival between pH 7 to 8.0. Viruses can survive pH 3.0 to 10.0. can survive pH 3.0 to 10.0.

Organic matterOrganic matter – lower survival in sewage – lower survival in sewage TurbidityTurbidity – longer survival in turbid waters – longer survival in turbid waters SedimentsSediments – longer survival in sediments. – longer survival in sediments.

Thermal stabilization of viral capsid. Bacteria are Thermal stabilization of viral capsid. Bacteria are protected from predation and more degradable protected from predation and more degradable organic matter in sediments organic matter in sediments

Factors Controlling the Survival of Factors Controlling the Survival of Enteric Pathogens in WaterEnteric Pathogens in Water

SaltsSalts – Shorter survival in seawater. – Shorter survival in seawater. Giardia dies quickly in seawater. Giardia dies quickly in seawater.

SunlightSunlight – UV light. Die-off of enteric – UV light. Die-off of enteric bacteria can be modeled using incidence bacteria can be modeled using incidence of UV light. Viruses more resistant to of UV light. Viruses more resistant to inactivation by UV light than bacteria.inactivation by UV light than bacteria.

Antagonistic microfloraAntagonistic microflora – Shorter survival – Shorter survival time in non-sterile environmentstime in non-sterile environments

Additional Factors Controlling the Additional Factors Controlling the Survival of Enteric Pathogens in SoilSurvival of Enteric Pathogens in Soil

Soil moistureSoil moisture – Generally longer survival – Generally longer survival at higher soil moistureat higher soil moisture

Type of soilType of soil – Longer survival in clay soils – Longer survival in clay soils and soils higher in organic matterand soils higher in organic matter

HydrophobicityHydrophobicity – shorter survival in – shorter survival in unsaturated soils do to inactivation at the unsaturated soils do to inactivation at the air water interfaceair water interface

Survival in Aerosols/FomitesSurvival in Aerosols/Fomites Suspending mediaSuspending media

Organic matter and salts can prolong survivalOrganic matter and salts can prolong survival Relative humidityRelative humidity

Rate of inactivation depends upon the Rate of inactivation depends upon the organismorganism

Rate of dryingRate of drying Outdoor air factorOutdoor air factor

Time

NumberOfOrganisms

Microbial Die-off

Microbial Die-off Microbial Die-off /Decay/Inactivation (Viruses)/Loss /Decay/Inactivation (Viruses)/Loss

of Infectivityof Infectivity

TT9999 = 99% Die-off = 99% Die-off

TT99.999.9 = 99.9% Die-off = 99.9% Die-off

N/NN/N00 = Log Survival = Log Survival

N = Concentration after a given period of N = Concentration after a given period of timetime

NN00 = Initial concentration of organisms = Initial concentration of organisms

Inactivation of Respiratory Viruses Inactivation of Respiratory Viruses on Fomiteson Fomites

0.0278 0.0417

0.1670.2

0.5

0.6250.667

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

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Inactivation of Enteric Viruses Inactivation of Enteric Viruses on Fomiteson Fomites

0.00210.00278 0.00278

0.0059

0.011

0

0.002

0.004

0.006

0.008

0.01

0.012

Astrovirus(serotype 4)

Hepatitis Avirus

Rotavirus p13 Calicivirus(feline strain

F9)

Adenovirus 40

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