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LSCI 230: Microbiology > Water-Borne Pathogens > Flashcards

Water-Borne Pathogens Flashcards

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1
Q

Water-borne pathogens

A
  • Transmission is mediated by fecal contamination of water supplies
  • Most of these pathogens grow in the intestinal tract
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2
Q

Source of infection of water-borne pathogens

A
  • Portable water
  • Recreational water
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3
Q

Water-borne pathogens and viruses

A
  • Salmonella typhi: typhoid fever in humans
  • Vibrio cholerae: cholera
  • Shigella spp.: shigellosis
  • Salmonella spp.: salmonellosis, gastroenteritis
  • Campylobacter spp.: gastroenteritis
  • Enterovirus: poliovirus, norovirus, rotavirus
  • Hepatitis A virus
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4
Q

Water-borne pathogenic protozoa

A
  • Giardia lamblia: Giardiasis
  • Cryptosporidium parvum: chronic & accute diarrhea

Both form cysts that are resistant to several disinfectants

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5
Q

Water quality control

A
  • Test the water for organisms that are present in large numbers in feces
  • use these organisms as indicators of fecal pollution
  • if these organisms are present, there is a chance that the water may also contain pathogens
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6
Q

2 indicators of water quality

A

Coliforms:
* facultative aerobic, Gram-negative, non spore-forming, rod-shaped bacteria
* ferment lactose with gas formation within 48 hours at 35°C.
* Includes a variety of bacteria not all of intestinal origin

Fecal coliforms:
* coliforms derived from the intestines of warm-blooded animals
* can grow at 44.5°C

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7
Q

Methods of testing water quality

A

Membrane filtration:
* Tests for coliforms and fecal coliforms
* Faster and easier than MPN

Most probably number (MPN):
* Test for coliforms
* Samples are added to lactose broth
* If gas production is detected, test is positive

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8
Q

Water treatment aims

A
  • Remove pathogens
  • Improve clarity of water
  • Remove compounds that give badsmell or taste
  • Soften the water
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9
Q

Water treatment steps

A
  1. Sedimentation
  2. Flocculation
  3. Filtration
  4. Disinfection
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10
Q

Sedimentation

A
  • Water is left to stand in a reservoir
  • Allow large particle (sands) to settle
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11
Q

Flocculation

A
  • A flocculating chemical is added
  • Water is transferred to a flocculation basin and allowed to settle for ~6h
  • As the flocs form, they trap fine particles
  • ~80% of bacteria, color & particulates have been removed
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12
Q

Filtration

A

The water is filtered through sand to remove remaining particles (cysts)
* 98-99.5% of the bacteria have been removed

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13
Q

Disinfection

A

Add disinfectant (Cl/O3)
* Kill remaining bacteria
* Neutralize chemicals that give water bad smell/taste

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14
Q

Residual chlorine

A

Amount of chlorine that remains in the water that left thetreatment plant
* Desired/required to protect the distribution system

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15
Q

Waste water treatment aims

A
  • Reduce BOD
  • Destroy pathogens
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16
Q

Wastewater treatment steps

A
  • Primary treatment
  • Secondary treatment
  • Tertiary treatment
17
Q

Primary treatment

A

Sedimentation tanks
* 40-70% of suspended solids settle
* Flocculating chemical can be added
* Produces 1° sludge
* Reduces the BOD of wastewater to 25-40% and bacteria by 25-75%

18
Q

Secondary treatment: Liquid

A

Trickling filter
* liquid is sprayed over a bed of rock, microorganisms form biofilms & oxidize the OM
* BOD reduced by 80-95%, bacteria by 90-95%

Activated sludge
* Air is blown through the liquid
* Slime-forming bacteria grow and clump together to form flocs that oxidize the OM
* Material passes to a settling tank, sludge is removed for disposal or 2° treatment
* BOD reduced by 85-95%, bacteria by 90-98%

19
Q

Secondary treatment: Sludge

A

1° & 2° sludge is subjected to microbial digestion under anaerobic conditions
* BOD reduced by 90%
* Material that remains is incinerated or buried

20
Q

Tertiary treatment

A

May involve any or a combination of the following:
* Biological treatment (ponds: algae)
* Flocculation
* Filtration
* Chlorination or ozonation

May be suitable for drinking

21
Q

Septic tank

A

Minimal treatment of sewage
* Settling of material + minimal sludge digestion
* requires periodic emptying
* BOD reduced by 60%
* Effluent flows to a leaching field where soil act as a filter and organisms decompose organic matter

LSCI 230: Microbiology (14 decks)

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