Microbiological Quality of Water

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Microbiological Quality of Water
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Microbial Indicators of Fecal Contamination

• Approach used to evaluate the quality of water
  for human use
• Quantification of bacteria normally found within
  the intestines of warm blooded animals
• High numbers is an indication of the presence of
  pathogens

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Criteria for an Ideal Indicator of Fecal
Contamination

• Applicable to all water sources
• Present in stools, sewage water, and water
  samples that contain pathogens

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Criteria for an Ideal Indicator of Fecal
Contamination

• Number correlated to level of fecal contamination
  and to number of pathogens
• No growth in the environment
• Survival/persistence that is longer than that of
  pathogens
• Easily detected and quantified
• Numbers associated to the risk of consumers of
  contracting enteric diseases

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Ideal Indicator

• Ex Mooneys Bay ? water quality warnings based
  on E.coli levels
• Representative of ALL potential sources
• To date no single indicator meets all the criteria

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Indicators of Fecal Contamination

• Coliform bacteria
• Bacteria of the Enterobacteriaceae family
• Includes 4 genera
• Enterobacter, Klebsiella, Citrobacter, and
  Escherichia
• Present in the intestine of most warm blooded
  animals (humans)
• Gram negative rods, non-sporulating
• Ferment lactose with acid and gas production in
  48 hours at 37C

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Fecal Coliforms

• Subset of total coliforms
• Escherichia coli (E. coli)
• Thermotolerant coliforms
• Grow and ferment lactose at 44oC
• Source Fecal material only
• Exception the tropics

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Fecal Streptococci

• Gram positive
• Mainly associated with animal intestines
• S.faecalis, S.faecium
• Longer survival time than coliforms
• Survive broad range of environmental conditions
  ex temperature, pH, salt
• The ratio between coliforms and Streptococci is
  used to confirm a contamination from human
  sources
• Ratio Escherichia/Streptococci greater than 0.7

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Tests for Fecal Contamination

• Selective media
• Allows the growth of certain genera
• Differential media
• Allows the visual discrimination of different
  genera

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Methods

• Presumptive tests
• MPN
• Viable counts

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Presumptive Tests

• Makes use of differential/selective media to
  detect characteristics common to indicator
  microorganisms
• Positive test presence suspected
• Negative test absence
• Most probable number (MPN)
• Probable number based on a statistical point of
  view

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Lactose Broth
A B C

• Presumptive test for total coliforms
• Differential medium
• Allows to detect lactose fermentation
• pH and gas indicators

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Presumptive Test for S. faecalis (Enterococcus)

• Selective medium
• Contains azide
• Selective for Enterococcus
• Differential
• Fermentation of glucose

1. Negative no acid
2. Positive presence of acid

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Food Microbiology
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Concerns

• Provide clean, healthy, and safe foods to
  consumers
• Prevent and retard spoiling
• Prevent food associated diseases
• Preservation and production of foods
• 1/3 of all foods are lost because of spoilage

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Sources of Bacteria in Foods
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Sources of Bacteria in Foods

• Soil and water
• Plants
• Equipment for the treatment and manipulation of
  food products
• Humans and Animals (Natural flora)
• Compost (fertilizer)
• Air/dust

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Spoilage

• Considerations
• Organoleptic properties
• Taste
• Smell
• Texture
• Appearance

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Bacteria Associated with Food Spoilage

• Meats
• Enteric bacteria
• Escherichia coli
• Salmonella
• Milk products
• Lactic bacteria
• Lactobacillus
• Fruits and vegetables
• Pseudomonas

Gram (-), short rods, facultative anaerobes
Gram (), short rods, non-spore forming
Gram (-), short rods, strict aerobes
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Types of Food Borne Diseases

• Food infections
• Usually associated with endotoxins
• Requires ingestion of pathogen
• Requires growth of pathogen in host
• Appearance of symptoms between 24-72 hours
• Often aggravated by the use of antibiotics
• Bacteriolytic antibiotics are not recommended
• Bacteriostatic antibiotics can help

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Types of Food Borne Diseases (Contd)

• Food intoxications
• Usually associated with exotoxins
• No infection
• Appearance of symptoms between 1-3 hours
• Antibiotherapy useless in the absence of
  infection
• Use of anti-toxins recommended

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Bacteria Associated with Food Infections

• E. coli O157H7
• Mostly associated with meats from beef and pork
• Normal inhabitant of the natural flora of the
  intestine
• Absent in muscles
• Contamination is usually the result of
  inappropriate manipulations
• Utensils
• Opening and spilling of intestines
• Skin of employees
• Endotoxin A (lipid A of LPS layer)

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E. coli O157H7 (Contd)

• Can be associated with fresh vegetables
• Can be associated to products said to be organic
  
• Contamination by animal and human compost
• Can be associated with water ex Walkerton, ON

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Salmonella sp.

• Mainly associated with the intestines of poultry
  and pork
• Can also be found on fresh vegetables just like
  E.coli
• Very low infectious dose
• lt 10 cells

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Bacteria Associated with Food Borne Intoxications

• Clostridium perfringens
• Gram Positive rods
• Spore former ? sometimes used as indicator
• Natural constituent of the natural flora of
  mammals (including humans) and birds
• Also found in soil and water
• Intoxications associated with foods prepared a
  few days in advance
• Intoxication caused by an enterotoxin
• Stomach aches and diarrhea

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Bacteria Associated with Food Borne Intoxications

• Clostridium Botulinum
• Gram Positive rods
• Spore former found in soil and water
• Intoxications associated with poorly sterilized
  cans of fruits and vegetables
• Also associated with food prepared a few days
  earlier
• Intoxication caused by a neurotoxin
• Flaccid paralysis, double vision, speech
  impediment, difficulty to swallow
• Death due to paralysis of respiratory system