Transcript Faecal Bacteria

Faecal Bacteria
 Objective
 To know the types of faecal bacteria prevalent in
the aquatic environment and their relevance to
Environmental Engineering
 To know the methods used to enumerate faecal
bacteria
 References
 Kiely - Environmental Engineering
 James A & Evison L - Biological Indicators of Water
Quality
 Lecture Outline
 Faecal Bacteria
 Methods of Enumeration
Faecal Bacteria
Non-Pathogenic
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Escherichia coli *
* indicator organisms
Streptococcus faecalis*
Lactobacillus sp.
Enterococcus faecalis, etc
Pathogenic
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TyphoidSalmonella typhi
Paratyphoid Salmonella paratyphi
Cholera
Vibrio cholera
Dysentery
Shigella dysenteriae
Weils Disease Leptospira interrogans (Leptospirosis)
(Protozoal Giardiasis; Amoebic Dysentery; Cryptosporidiosis.
ViralPolio, Hepatitis A, Gastro enteritis, Aseptic Meningitis, etc.)
Problems in Counting Pathogens
Techniques Complicated
Tissue Culture (Viruses)
Cell Enrichment (Bacteria)
Techniques Protracted
Viruses 2+ weeks
Bacteria 1 week
Better to count Indicator Organisms
 Present in faeces always.
 Indicate the possible presence of a Pathogen
Properties of an ‘Ideal’ Indicator Bacteria
Should be:
Present in high numbers.
Specific to faecal material.
Identified by simple consistent tests.
non-pathogenic.
Behave in a similar way to pathogens in the
environment.
Survival rate same or better than pathogens.
As resistant or more resistant than pathogens to
disinfection.
Bacterial Indicators in Common Use
(1)
Total Coliforms (TC)
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Escherichia, Citrobacter, Klebsiella, Enterobacter.
Gram negative rods, ferment lactose to acid + gas at 37C
Bile (detergent) tolerant - basis of selective media
Not always restricted to Faeces
Further identification by IMViC Tests
Indole production, Methyl Red test, Voges-Proskauer test, Citrate
utilization, plus growth at 44.5 C
Bacterial Indicators in Common Use
(2)
Thermotolerant Coliforms (TTC)
or Faecal Coliforms (FC)
 as for Total Coliforms but can grow and ferment lactose
at 44.5 C
 mainly Escherichia coli but includes Citrobacter,
Klebsiella, Enterobacter
Escherichia coli (E. coli)
 as above but can also produce Indole from Tryptophan
at 44.5 C
 Always restricted to Faeces
Bacterial Indicators in Common Use
(3)
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Faecal Streptococci (FS)
Confirm conflicting results from (1) and (2)
Better survival then E.coli in cold waters
Greater resistance to chlorine
Better survival at sea.
Distinguish between Animal and Human pollution.
Man
Sheep
Cow
Pig
FC/FS Ratio
> 4.4
0.4
0.2
0.04
Caution
only valid for fresh
polluion < 24 h.
(differential die-off)
APHA now recommends use of Streptococcus bovis (animals) and
Enterococcus faecalis (man)
Bacterial Indicators in Common Use
(4)
Clostridium perfringens
 Resistant spores - long survival in water and sediments.
– Use to detect remote pollution when few samples taken. e.g. farm
supplies, wells, springs.
 Survives chlorination
– Use to check Chlorination efficiency.
 Survives seawater very well.
– Use to check sewage contamination of sea bed.
Organisms Present in Raw Sewage
Harmless Bacteria
 E. coli, Coliforms
 Faecal Streptococci
105 - 109 /100ml
Pathogenic Bacteria
 Salmonella typhi
 Vibrio cholera
 Shigella
103 - 104 /100ml
 Protozoal
Entamoeba hystolytica
 Viral
Polio, Coxsackie, Adenovirus 105 - 109 PFU/l
 Helminths
Schistosoma, Ascaris, Taena
5 - 80% of population
102 /l
Legionnaires’ Disease (Legionellosis)
 Legionella pneumophila
 fever, headache, respiratory symptoms, pneumonia
 Opportunist pathogens
 aquatic and terrestrial habitats
 Water systems
 cooling towers, spa baths, fountains, distribution mains, air
conditioning
 20 C minimum
 stagnation
 Aerosol formation
 Risk Assessment
 Monitoring
– Heterotrophic Plate Count
– Immunological probes (confirmation)
 Prevention
– eliminate growth conditions
– DISINFECTION
Enumeration
Why enumerate bacteria
 Quality – Abstraction (75/440/EEC; 79/869/EEC)
– Bathing (76/160/EEC)
– Drinking (80/778/EEC)
 Risk Assessment
– Disease prevention
– Ingestion by Faecal-Oral Route
– Aerosols
Enumeration
How to Enumerate Bacteria
 Counting by Microscopy
– Specific Stains
– Time required
 Culture Techniques
– Plate Counts
– Selective Agar
– Multiple Tube Method
– Most Probable Number (MPN)
– Membrane Filtration
Enumeration
Sample Preparation
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Collection
Transport and Storage (6 h max, cool)
Aseptic Technique
Dilution to Extinction
Interpretation of Results
 sources of error
– moribund and stressed cells
– clumping and dispersion
– experimental
 Means
– arithmetic (normal distribution)
– geometric (skewed distribution)