Microbiology of Water Water Analysis Experiment 50

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Microbiology of WaterWater AnalysisExperiment
50
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Why Test Water

• Water has become a formidable factor in disease
  transmission
• Polluted water contains vast amounts of organic
  matter
• Organic matter is excellent nutritional source
  for growth and multiplication of microorganisms
• Nonpathogenic not major concern
• Intestinal contaminants of fecal origin are

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4 Classes of Communicable Diseases

• 1. Food water
• E.coli undercooked meat
• 2. Airborne
• Tuberculosis
• 3. Arthropods
• Ticks mosquitoesmalaria, lymes disease
• 4. Contact
• Direct-physical contact or Indirect-cough
  droplets

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Why Potable Water

• Intestinal Infections
• Dysentery, typhoid fever, cholera
• Parasites
• Helminths, guinea worms, flukes

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What to Test For

• Water is tested for Escherichia coli
• Bacterium indicative of fecal pollutions
• Normally present in human intestine
• Alerts officials to possible presence of other
  pathogens
• Some regions bacteria normal in soil
• Qualitative Quantitative Methods

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Qualitative Analysis

• 3 Basic Tests
• 1) Presumptive
• 2) Confirmed
• 3) Completed

Detect presence of Coliform bacteria Gram
(-) Nonspore-forming bacilli Lactose fermenters
with acid and gas Incubate at 37C Detectable
in 24 hours
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Presumptive Test

• Determines most probable number of bacteria
• ObjectiveDetermine presence of bacteria
• Obtain index indicating the most
  probable number of organisms in
• the sample (MPN) test
• Gas in Durham tube is the presumptive evidence

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Presumptive test results
Tube 1  Positive for fecal coliforms.  Note (1)
the gas present in the Durham tube and (2) the
color change from red to yellow as acid
end-products react with the pH indicator. Tube
2  Negative for fecal coliforms.  Note the
absence of gas in the Durham tube.  Even though
the pH indicator has changed from red to yellow,
gas must be produced for a positive result. Tube
3  Negative for fecal coliforms.
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Confirmed Test

• ObjectiveConfirm presence of bacteria
• for the positive presumptive
• Why? Presumptive suggests nonpotable so
• confirm organism isnt of noncoliform
• origin recognized by this test
• (false positive)

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Confirmed Test

• Use selective differential media (EMB)
• Streak from the () presumptive tube
• Methylene blue dye inhibits ()
• Acidic environment, precipitates out onto
  coliform colonies

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Completed Test

• ObjectiveConfirm presence of coliform
  bacteria in water sample
• Final analysis
• examine colonies
• on EMB

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Procedure for Water Analysis

• We are adjusting the test for this lab
• Working in your group by rows
• 1. Presumptive Inoculate 3 tubes
• lactose broth w/ Durham tubes
• .1ml 1ml 10mls
• 2. Confirmed test Inoculate 2 EMB
• plates
• 3. Incubate at 37C read Thursday

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Procedures for Thursday

• Look for gas production in Durham tubes
• Look for the green sheen of E. coli
• Record results of Durham tube test on board
• Calculate MPN per 100ml
• Do a gram stain
• Do a spore stain
• Confirm morphology

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FYI

• Key reaction in lab procedure for determining
  potability of water is the lactose fermentative
  ability
• National Standard specifies water safe for
  consumption if it does not contain more than an
  average of 1 coliform per 100ml of water