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Microbial Survival in the Environment: with Special Attention to Enteric and Respiratory Pathogens. Mark D. Sobsey ENVR 421. Microbe Transmission Routes. Direct Contact (Person to Person) Indirect Contact Vector Transmission Biological Mechanical Vehicle Transmission

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Microbial survival in the environment with special attention to enteric and respiratory pathogens l.jpg

Microbial Survival in the Environment: with Special Attention to Enteric and Respiratory Pathogens

Mark D. Sobsey

ENVR 421

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Microbe Transmission Routes Attention to Enteric and Respiratory Pathogens

  • Direct Contact (Person to Person)

  • Indirect Contact

    • Vector Transmission

      • Biological

      • Mechanical

    • Vehicle Transmission

      • Respiratory transmission (by droplets or aerosols)

      • Fecal-oral transmission (by ingestion of air-borne contaminants, and contaminated foods or water

      • Fomite transmission and self-inoculation after contact with fomitic surfaces

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For microbes transmitted by respiratory and fecal-oral routes, transport and persistence in the environment is related to risk of host exposure, infection, and disease

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  • Greater Inactivation/death rates at higher temperatures

  • Lower survival rates at higher temperatures

    • But, some microbes will grow or grow better at higher temperatures

  • Many microbes survive better at lower temperature

    • Some bacteria experience “cold injury” or“cold shock” and cold inactivation

  • Thermal inactivation differs between dry heat and moist heat

    • Dry heat is much less efficient than moist heat in inactivating microbes

  • Some microbes survive very long times when frozen

    • Other microbes are destroyed by freezing

      • Ice crystals impale them

  • Increased environmental temperatures can promotes pathogen spread by insect vectors (mosquitoes, flies, etc.)

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pH Environment

  • Relative acidity or alkalinity

  • A measure of hydrogen ion (H+) concentration

  • Scale:

    • 1 (most acidic) to 14 (most alkaline or basic)

    • pH 7 is neutral

    • Moving toward pH 1 the substance is more acidic

    • Moving toward pH 14, the substance is more alkaline.

  • Extreme pH inactivates microbes

    • Chemically alters macromolecules

    • Disrupts enzyme and transport functions

    • Some enteric pathogens survive pH 3.0 (tolerate stomach acidity)

    • Some pathogens survive pH 11 and fewer survive pH 12

Microbes are most stable in the environment and will grow in media (e.g., foods) in the mid pH range

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Moisture Content or Water Activity Environment

  • Drying or low moisture inactivates/kills some microbes

    • Removing water content of some foods can preserve them

    • Most viruses rapidly inactivated in soil at <1% moisture; sme at a few%

  • Moisture content of foods is measured as water activity, Aw.

    • Aw: ratio of the water vapor pressure of the substrate to the pressure of pure water at the same temperature.

    • Vapor pressures is hard to calculate, so an alternative method is used to measure Aw in food science:

    • Aw = moles of water ÷ (moles of water + moles of solute)

    • Pure water has a water activity of 1.00.

    • If 1 mole of a solute is added, then the solution has an Aw of 0.98.

    • Aw is measured on a scale of 0.00 to 1.00.

    • Most fresh foods have a water activity of 0.99.

    • Most spoilage microbes do not survive if an Aw below 0.91.

      • some yeasts and molds that can survive at water activity of 0.61.

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Physical Factors Influencing Survival, Continued Environment

  • Ultraviolet radiation: about 330 to 200 nm

    • Primary effects nucleic acids; absorbs the UV energy and is damaged

  • Sunlight:

    • Ultraviolet radiation in sunlight inactivates microbes

    • Visible light is antimicrobial to some microbes

      • Promotes growth of photosynthetic microbes

  • Ionizing radiation

    • X-rays, gamma rays, beta-rays, alpha rays

    • Generally antimicrobial; bacterial spores relatively resistant

    • Main target of activity is nucleic acid

    • Effect is proportional to the size of the “target”

      • Bigger targets easier to inactivate; a generalization; exceptions

    • Environmental activity of ionizing radiation in the biosphere is not highly antimicrobial

    • Ionizing radiation is used in food preservation and sterilization

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Atmospheric and Hydrostatic Pressure Environment

  • Most microbes survive typical atmospheric pressure

  • Some pathogens in the deep ocean are adapted to high pressure levels (hydrostatic pressures): barophiles

    • Survive less well at low atmospheric pressures

    • Spores and (oo)cysts survive pressure extremes

  • High hydrostatic pressure is being developed as a process to inactivate microbes in certain foods, such as shellfish

    • Several 100s of MPa of pressure for several minutes inactivates viruses and bacteria in a time- and pressure-dependent manner

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Role of Solids-Association in Microbial Survival Environment

Clumped: interior microbes protected

  • Microbes can be on or in other, usually larger particles or they can be aggregated (clumped together)

  • Association of microbes with solids or particles and microbial aggregation is generally protective

  • Microbes are shielded from environmental agents by association with solids

    • Protection depends on type of solids-association

    • See diagrams, right

  • Protection varies with particle composition

    • Organic particles: often highly protective

      • Biofilms protect microbes in them

      • React with/consume antimicrobial chemicals

    • Inorganic particles vary in protection

      • Opaque particles protect from UV/visible light

      • Inorganic particles do not always protect well against chemical agents

    • Some inorganic particles are antimicrobial

      • Silver, copper, other heavy metals/their oxides

Adsorbed: partially protected







: Antimicrobial agent

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Chemicals and Nutrients Influence Microbial Survival Environment

  • Antimicrobial chemicals

    • Strong oxidants and acids

    • Strong bases

    • Ammonia: antimicrobial at higher pH (>8.0)

    • Sulfur dioxide and sulfites: used as food preservatives

    • Nitrates and nitrites: used as food preservatives

    • Enzymes:

      • Proteases

      • Nucleases

      • Amylases (degrade carbohydrates)

    • Ionic strength/dissolved solids/salts

      • High (or low) ionic strength can be anti-microbial

        • Many microbes survive less in seawater than in freshwater

        • High salt (NaCl) and sugars are used to preserve foods

          • Has a drying effect; cells shrink and die

    • Heavy metals:

      • Mercury, lead, silver, cadmium, etc. are antimicrobial

  • Nutrients

    • for growth and proliferation

    • Carbon, nitrogen, sulfur and other essential nutrients

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Biological Factors Influence Microbial Survival Environment

  • Chemical antagonistic activity by other microorganisms:

    • Proteolytic enzymes/proteases

    • Nucleases

    • Amylases

    • Antibiotics/antimicrobials: many produced naturally by microbes

    • Oxidants/oxides

    • Fatty acids and esters; organic acids (acetic, lactic, etc.)

  • Predation

  • Vectors

  • Reservoir animals

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Factors Affecting Survival in Liquid Environment

  • Temperature

  • Ionic Strength

  • Chemical Constituents/Composition of Medium

  • Microbial Antagonism

  • Sorption Status

  • Type of Microbe

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Factors Affecting Survival in Aerosols Environment

  • Temperature

  • Relative Humidity

  • Moisture Content of Aerosol Particle

  • Composition of Suspending Medium

  • Sunlight Exposure

  • Air Quality (esp. “open air” factor)

  • Size of Aerosol Particle

  • Type of Microbe

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Factors Affecting Survival on Surfaces Environment

  • Type of Microbe

  • Type of Surface

  • Relative Humidity

  • Moisture Content (Water Activity)

  • Temperature

  • Composition of Suspending Medium

  • Light Exposure

  • Presence of Antiviral Chemical or Biological Agents

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Effect of Virus Type on Survival Environment

  • Differences between virus families

    • Clear differences between enveloped and non-enveloped viruses (Mahl, 1975)

  • Differences between virus genera

    • Differences between Enteroviruses and Rhinoviruses

  • Differences between virus strains

    • Survival of Influenza and Pseudorabies virus has been shown to be strain dependent (Platt, 1979; Mitchell, 1972)

  • Differences associated with passage in different host cells

    • Ex. Yellow fever virus inactivation sensitivity at intermediate RH increases with passage in HeLa cells (Hearn, 1965)

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Microbe Survival in Liquid Media Environment

  • Temperature

    • Increased inactivation with increasing temperature

    • Most are inactivated rapidly (minutes) above 50oC

    • Some microbes are more thermotolerant than others (e.g. Hepatitis A virus, bacterial/fungal spores, some helminth ova (ascarids)

      • Most are inactivation more at higher temperatures

      • Chemical composition of media influences survival

        • Protein/other organics & Mg&Ca ions protect

    • Generally very stable at ultra-cold temperatures,

      • Some loss of infectivity occurs with freezing and thawing

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Survival in Liquid Media Environment

  • pH

    • Direct effects on conformation of proteins and other biomolecules

    • Indirect effects on adsorption and elution from particles

    • pH range of stability is microbe-dependent

      • Polio: 3.8 to 8.5 for maximum stability

  • Salt Content

    • Variable effects on microbe survival

    • Affects microbe physiology (isotonic conditions), adsorption and stability of biomolecules

    • Divalent cations (Mg2+) can increase thermo-stability of viruses and bacteria

      • E,g., MHV, enteroviruses, HAV

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Microbe Survival in Liquid Media Environment

  • Microbial Antagonism

    • Microflora influences microbe survival

      • Metabolites: enzymes, VFAs, NH3 are antiviral

    • Use of pathogen as a nutrient source

    • Greater microbe survival documented in sterilized or pasteurized matrices, as compared to non-sterile matrices

    • Phenomena demonstrated in sewage, fresh, estuarine, and marine waters, soils and sediments.

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Microbe Survival in Liquid Media Environment

  • Adsorption

    • Several possible mechanisms:

      • Ionic attractions and repulsions

      • covalent reactions (with active chemicals)

      • hydrogen bonding

      • hydrophobic interactions

      • double layer interactions

      • van der Waal’s forces

    • Adsorption status greatly influences survival

      • adsorbed microbes generally survive longer than unadsorbed microbes

      • Protection and accumulation in sediments and soils

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Colloidal Particles and their Charge Properties Environment

  • Colloids: small charged, suspended particles

    • Most microbes are colloids

  • Particle surface is charged

    • strongly bound layer of opposite charged counterions; the Stern layer

    • Positive ions are attracted by a negative colloid and vice-versa

  • Stern layer: layer of actual particle and its immediately bound counter ions.

  • Beyond Stern layer: diffuse layer of ions that move with the particle when it is in motion

  • Zeta potential : potential at the shear plane; the layer of bound ions moving with the particle

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Aqueous Liquids on Hydrophilic and Hydrophobic Surfaces Environment

  • Water is polar and hydrophilic

  • Droplets spread out on hydrophilic (polar) surfaces

  • Droplets form a round bead on hydrophobic (non-polar) surfaces

  • Contact angle: angle describing the interaction of a water droplet with a surface

  • Influence microbe survival on surfaces

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MicrobeSurvival in Liquid Media Environment

  • Organic Matter

    • In liquid media, organic matter increases microbe survival

      • Increased oxidant demand protects from oxidation

      • If an enzyme substrate, protects from enzymatic attack

      • Can coat to protect microbe particles

    • In soils, organic matter has variable effects on microbes

      • Possible competition for adsorption sites

      • May coat or protect microbe particles

      • Bacteria may grow of organics are nutrients

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Microbe Survival in Liquid Media Environment

  • Antimicrobial Chemicals

    • Ionic and non-ionic detergents, particularly for enveloped viruses and some bacteria

    • Ammonia is virucidal; ammonium ion is not

    • Germicides (chlorine, ozone, etc.)

  • Light

    • Direct microbicidal activity below wavelengths of 370 nm

    • Indirect antimicrobial activity:

      • stimulation of microflora growth

      • triggering formation of reactive oxidants

      • activation of photoreactive chemicals

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Microbe (Virus) Survival in Aerosols Environment

  • Relative Humidity and Moisture Content

    • Viruses with lipid survive better at lower relative humidity

    • Viruses with little or no lipid content survive better at higher relative humidity

    • Viral inactivation or retention of infectivity may be a function of stabilization (drying of aerosol) and of rehumidification of aerosol particle upon collection

    • Effect of relative humidity on virus survival may be influenced by temperature effects

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Microbe Survival in Aerosols Environment

  • Temperature

    • Survival decreases with increased temperature

  • Suspending Media

    • composition influences microbe stability

    • effect is microbe dependent

      • Salts stabilize some viruses (e.g. Poliovirus)

      • Removal of salts stabilize other viruses (e.g. Langat, Semiliki Forest virus)

      • Proteinacious material and organic matter may have similar mixed effects, depending on microbe type

      • Polyhydroxy compounds stabilize some virus types (e.g. Influenza) but have no effect on other viruses

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Microbes Survival in Aerosols Environment

  • Oxygen and Air Ions

    • Oxygen has little direct effect on most viruses but may influence bacteria

    • But, oxygenation may be synergistic with higher temperature and sunlight to inactivate microbes

    • The “Open Air Factor” has been shown to have virucidal activity

      • Poorly characterized chemical agents in open air that reduce virus survival compared to clean laboratory air

      • May be reaction products of ozone and olefins

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Microbe Survival in Aerosols Environment

  • Light

    • Virucidal activity of UV light is a greater in air than in liquid media

    • Photosensitivity is virus type-dependent and may be related to the envelope

      • Non-enveloped viruses (Poliovirus, Adenoviruses and FMDV) are more resistant to UV light than enveloped viruses (vaccinia, herpes simplex, influenza, and Newcastle disease virus) (Jenson, 1964; Donaldson 1975; Applyard, 1967)

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Microbe Survival in Aerosols Environment

  • Aerosol Particle Size

    • Airborne microbes may be more rapidly inactivated in smaller aerosol particles than larger ones (some studies)

    • Other studies observed no effect of particle size on virus survival

  • Aerosol Collection Method

    • Abrupt rehydration of virus particles and other microbes upon collection may lead to their inactivation

    • Prehumidification may improve recovery of infectious virus

    • Effect is virus type-dependent

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Microbe Survival on Surfaces Environment

  • Adsorption State

    • Air Water Interface

    • Triple Phase Boundary

  • Physical State

    • Dispersed

    • Aggregation

    • Solids associated

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Microbe Survival on Surfaces Environment

  • Relative humidity

    • Similar effects as seen in aerosols; effects are microbe type dependent

  • Moisture Content

    • In soils moisture content directly related to microbe survival

      • Dessication

      • Enhanced predation

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Microbe Survival on Surfaces Environment

  • Temperature

    • Effects as observed in liquid media and aerosols

    • Interaction between relative humidity and temperature pronounced on surfaces for certain virus types (e.g. Polio, Herpes Simplex), less important for others (e.g. Vaccinia) (Edward, 1941)

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Microbe Survival on Surfaces Environment

  • Suspending Media

    • Effects similar to effects on survival in aerosols

      • Presence of fecal material

      • Presence of salts

  • Type of Surface

    • Little effect by non-porous surfaces on most viruses

      • important for some virus types (Herpes simplex)

    • Effects more pronounce for porous surfaces (e.g. fabrics: cotton, synthetics and wool

  • Light

    • Effects similar to those in aerosols and liquids

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Least Environment


Microbe type: Resistance to chemical disinfectants:

  • Vegetative bacteria: Salmonella, coliforms, etc.: low

  • Enteric viruses: coliphages, HAV, Noroviruses: moderate

  • Bacterial Spores

  • Fungal Spores

  • Protozoan (oo)cysts, spores, helminth ova, etc.

    • Cryptosporidium parvum oocysts

    • Giardia lamblia cysts

    • Ascaris lumbricoides ova

    • Acid-fast bacteria: Mycobacterium spp.


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Virus Survival in Drinking Water Environment

  • Non-Enveloped Viruses

    • Poliovirus survives in sterile water for nearly 300 days (Schwartzbrod, 1975)

    • Astroviruses survive up to 90 days in dechlorinated drinking water (Abad, 1997)

  • Enveloped Viruses

    • Herpes Simplex Virus survives in distilled water for up to 1 day and in tap water for up to 4 hours (Nerurkar, 1983)

    • Psuedorabies virus survives in chlorinated tap water for less than one day (Schoenbaum, 1990)

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Virus Survival in Fresh Water Environment

  • Non-Enveloped Viruses

    • Coxsackie virus survives up to 30 days in stream water with a 2 log10 reduction

    • From epidemiologic evidence Noroviruses survive at least 4 months in fresh water (Kukkula, 1999)

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Virus Survival in Soil/Groundwater Environment

  • Non-Enveloped Viruses

    • groundwater velocity models: survival in groundwater calculated to be up to 200 days (Vaughn, 1983)

    • Echovirus survival in sandy soil: 170 days in seeded studies (Bagdasaryan, 1964)

    • Seeded studies: Poliovirus, Norwalk, and MS2 detected in soil suspensions up to 70 weeks by RT-PCR; Infectious Polio was still detected in Groundwater after 70 weeks (Meschke, 2001)

  • Enveloped Viruses

    • Pseudorabies virus persists in well water up to 7 days

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Virus Survival in Sea/Brackish Water Environment

  • Non-Enveloped Viruses

    • Coxsackie A9 virus survives in marine waters for up to 30 days with ≤2 log10 reduction (Nasser, 2003)

      • Similar survival of HAV, FCV, and Polio (Callahan, 1995; Kadoi, 2001; and Wait, 2001)

  • Enveloped Viruses

    • Bovine Diarrhea Virus survives in various water types 6 to 24 days (Pagnini, 1984)

    • Viral Hemorrhagic Septicemia virus persisted up to 40 hours in filtered Seawater with 50% reduction; survival up to 36 days in cell culture medium-amended seawater

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Virus Survival in Fecal Waste Environment

  • Non-Enveloped Viruses

    • In animal wastes, rotavirus survival to > 6 months, 1 log10 reduction (Pesaro, 1995)

    • FMDV persist up to 100 days in a fecal slurry (Bartley, 2002)

    • Poliovirus persists up to 180 days in sand saturated with septic liquor (Yeager, 1979)

  • Enveloped Viruses

    • In animal wastes, herpes virus reduced 1 log10 in less than 1 week (Pesaro, 1995)

    • Pseudo rabies virus survives up to 2 weeks in swine urine; <2 days in lagoon and pit effluent (Schoenbaum, 1990)

    • Swine Fever Virus survives up to 15 days in manure (Have, 1984)

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Virus Survival in Aerosols Environment

  • Non-Enveloped Viruses

    • Rotavirus SA11 survives up to 223 hours, depending on humidity (Sattar, 1984)

    • Rhinovirus persists up to 24 hours with <1 log10 reduction

  • Enveloped Viruses

    • Vaccinia, VEE, and Influenza virus survive in aerosols for up to 23 hours (Harper, 1961)

    • New Castle Disease Virus persists 4-16 hours (Hugh-Jones, 1973)

    • Human Coronavirus (229E) persists at 50% humidity with up to 20% infectious at 6 days (Ijaz, 1985)

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Virus Survival on Surfaces Environment

  • Non-Enveloped Viruses

    • Poliovirus survives up to 20 weeks on wool blanket fabric (Dixon, 1966)

    • HAV recovered from stainless steel surfaces after 96 hours; and from plastic surfaces after 1 month (Mbithi, 1991)

    • Rotavirus persists for up to 10 days (Sattar, 1986)

  • Enveloped Viruses

    • Influenza persists for several weeks on dust, cotton sheets, and glass slides (Edward, 1941)

    • RSV was reduced by 2 log10 after 24 hours (Kingston, 1968)

    • Parainfluenza virus persists up to 12 days on plastic surfaces (Parkinson, 1983)

    • Human Coronavirus persists up to 6 hours with 1-2 log10 reduction