Download Microbial Survival in the Environment: with Special Attention to

Microbial Survival in the Environment:
with Special Attention to Enteric and
Respiratory Pathogens
Mark D. Sobsey
ENVR 133
Microbe Transmission Routes
• 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 airborne contaminants, and contaminated foods
or water
• Fomite transmission and self-inoculation after
contact with fomitic surfaces
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
Some Physical Factors Influencing
Microbe Survival in the Environment
TEMPERATURE
• 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.)
• Relative acidity or alkalinity
• A measure of hydrogen ion (H+)
concentration
• Scale:
pH
– 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
Moisture Content or Water Activity
• 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.
Physical Factors Influencing Survival, Continued
• 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
Atmospheric and Hydrostatic Pressure
• 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
Role of Solids-Association in Microbial Survival
• 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
Clumped: interior
microbes protected
Adsorbed:
partially
protected
Embedded:
most
protected
Dispersed:
least
protected
: Antimicrobial agent
Some Chemical Factors Influencing
Microbe Survival in the Environment
Effects
Chemicals and Nutrients Influence Microbial Survival
• 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
Some Biological Factors Influencing
Microbe Survival in the Environment
Effects
Biological Factors Influence Microbial Survival
• 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
Factors Affecting Survival in Liquid
• Temperature
• Ionic Strength
• Chemical Constituents/Composition of
Medium
• Microbial Antagonism
• Sorption Status
• Type of Microbe
Factors Affecting Survival in Aerosols
•
•
•
•
•
•
•
•
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
Factors Affecting Survival on Surfaces
•
•
•
•
•
•
•
•
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
Effect of Virus Type on Survival
• Differences between virus families
– Clear differences between enveloped and nonenveloped 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)
Microbe Survival in Liquid Media
• 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
Survival in Liquid Media
• 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 thermostability of viruses and bacteria
• E,g., MHV, enteroviruses, HAV
Microbe Survival in Liquid Media
• 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.
Microbe Survival in Liquid Media
• 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
Colloid Particles and their Surface Electrical Potentials
Colloidal Particles and their Charge Properties
• 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
Aqueous Liquids on Hydrophilic
and Hydrophobic Surfaces
• 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
MicrobeSurvival in Liquid Media
• 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
Microbe Survival in Liquid Media
• 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
Microbe (Virus) Survival in Aerosols
• 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
Microbe Survival in Aerosols
• 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
Microbes Survival in Aerosols
• 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
Microbe Survival in Aerosols
• 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)
Microbe Survival in Aerosols
• 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
Microbe Survival on Surfaces
• Adsorption State
– Air Water Interface
– Triple Phase Boundary
• Physical State
– Dispersed
– Aggregation
– Solids associated
Microbe Survival on Surfaces
• 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
Microbe Survival on Surfaces
• 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)
Microbe Survival on Surfaces
• 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
Microbe type: Resistance to chemical disinfectants:
• Vegetative bacteria: Salmonella, coliforms, etc.:
Least
low
• Enteric viruses: coliphages, HAV, Noroviruses:
moderate
• Bacterial Spores
• Fungal Spores
• Protozoan (oo)cysts, spores, helminth ova, etc.
– Cryptosporidium parvum oocysts
High
– Giardia lamblia cysts
– Ascaris lumbricoides ova
– Acid-fast bacteria: Mycobacterium spp.
Most
Virus Survival in Drinking Water
• 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)
Virus Survival in Fresh Water
• 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)
Virus Survival in Soil/Groundwater
• 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 RTPCR; Infectious Polio was still detected in
Groundwater after 70 weeks (Meschke, 2001)
• Enveloped Viruses
– Pseudorabies virus persists in well water up to 7 days
Virus Survival in Sea/Brackish Water
• 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 mediumamended seawater
Virus Survival in Fecal Waste
• 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)
Virus Survival in Aerosols
• 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 (HughJones, 1973)
– Human Coronavirus (229E) persists at 50% humidity
with up to 20% infectious at 6 days (Ijaz, 1985)
Virus Survival on Surfaces
• 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