Pathogens and Environments

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Pathogens and Environments
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Environments where pathogens survive
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Environments
AIR
SOIL
WATER
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Environments revised.
AIR
SOIL
WATER
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Soil
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Soil Texture vs Soil Structure
Soil texture distribution of sand, silt, clay
coarse
medium
fine
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Soil Texture vs Structure

• Soil structure aggregation

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Cation Exchange interchange between a cation in
solution and another cation on the surface of
any negatively charged material such as clay or
organic matter
Cation Exchange Capacity the ability of soil to
hold on to cations
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Cation Exchange

• Is influenced by
• strength of adsorption (adsorption affinity)
• Strong adsorption
• Al3 gt Ca2 Mg2 gt K NH4 gt Na gtH
• Weak adsorption
• the relative concentration of the cations in the
  soil solution.

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Microbes stick to clay particles

• By electrostatic forces
• By gluing themselves

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Do microbial ecologistseven care about soil
texture/structure
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Fates of Pathogens in Soils
Pathogens in organic waste
Losses due to die-off, predation
retention by soil particles
regrowth
waste-particle associated
leaching
alternate hosts (amoeba,plants, etc)
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Soil Water
Soil Water Potential the absolute potential
energy cannot be measured. essentially, SWP
ability of water to move

• Water film doesnt move
• Capillary
• Free water

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Soil and Subsurface Environments
Surface Soil Horizons O organic A surface
horizon fully decomposed organic minerals B
zone of illuvation (deposition) C unweathered
bedrock R bedrock Vadose Zone Aquifer
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Pathogens in Soils

• Metabolic state
• culturable counts are low (viable non-culturable
  state)
• Soils is where pathogens may be acquiring
  antibiotic-resistance plasmids

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Abiotic Selective Pressures

• Nutrient availability
• Iron (insoluble at neutral and basic pH)
• Micronutrients C, N, P
• Osmotic stress
• Adapt by accumulating compatible solutes
• Solutes that can accumulate without disrupting
  cell functions

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Biotic stressors

• Predation by soil eukaryotes (worms, protozoa)
• Legionella adapted to live within amoeba
• Salmonella, Pseudomonas aeruginosa can infect
  nematodes (and probably other soil eukaryotes)
• Pseudomonas makes phenazine pigments with dual
  functions eukaryotic toxins and iron acquisition
• Predation by other microbes (more later)

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Summary Survival in a soil environment

• VBNC
• Alternate hosts
• Biofilm formation
• Attached multicellular microbial communities
• Protected by extracellular polymers
• Osmoadaptation