Chapter 43 Flashcards
True or False: There was an increase in the number of sick cases caused by water contamination around 1910
FALSE: there was a decrease!
List 3 major water-borne pathogens
Bacteria: Salmonella, Shigella, Campylobacter, E coli, Legionella, Vibrio cholera
Virus: Norwalk, Enterovirus, Hep A, Rotavirus
Eucaryotes: Giardia lamblia, Cryptosporidium, Cyclospora (tend to happen in mountaineous areas because of runoff)
Name the pathogenic strain of E. coli responsible for causing bloody diarrhea, vomiting and dehydration.
O157:H7
Describe what happened during the Walkerton tragedy.
Walkerton is a farming community whose sole source of water is groundwater, and only one well was being used at the time so it had to be monitored regularly. Walkerton’s PUC took samples of the water and found high amounts of E. coli in the water, but failed to share that information. There were thousands of sick cases and seven deaths.
True or False: 75% of fecal matter from humans is bacteria.
FALSE: Actually 60%.
List the characteristics of an “ideal” indicator organism.
- Suitable for analysis of all types of water
- Present whenever enteric (gut) pathogens are present
- Survives longer than hardiest enteric pathogen(s)
- Does not reproduce in contaminated water
- Detected by highly specific test (easy to do + sensitive)
- Harmless to humans
- Level in water reflects degree of fecal pollution
What are the four commonly used indicator organisms?
TFFE (“To Fly ForEver”)
- Total coliforms
- Fecal coliforms
- Fecal streptococci
- Enterococci
True or False: If fecal coliforms are present, there’s a higher chance there is E. coli contamination in the water.
TRUE
True or False: If a pathogenic strand of E. coli is present, there’s a higher chance total coliforms are present.
FALSE: if E. coli is present, there’s a higher chance a pathogenic strain is present.
How does one detect whether fecal coliforms are present in a sample of total coliforms?
- Fecal detected by growing at 44-45ºC
- Beta-glucuronidase activity
True or False: Coliforms include all aerobic and facultative anaerobic, G+ nonsporing rod-shaped bacteria that ferment lactose with gas formation within 48h at 35ºC
FALSE: all conditions applicable to G- specimens, NOT G+
Coliforms include all __________ and facultative __________, nonsporing, rod-shaped bacteria that develop a __________ sheen within __h at __ ºC on _______ medium containing __________.
Coliforms include all AEROBIC and facultative ANAEROBIC, nonsporing, rod-shaped bacteria that develop a METALLIC sheen within 24h at 35 ºC on ENDO medium containing LACTOSE.
Describe the “multiple tube fermentation test” (MPN) to test for indicator organisms.
- Samples taken and different concentrations of the sample are placed in test tubes with media.
- Tubes go through the first round of lactose fermentation (if gas is produced, the specimen can ferment lactose and we’re on to the next round)
If gas production occurs, there’s a high chance total coliforms are present!
True or False: WHO’s drinkable water criteria involves achieving 0-0-0 on all three MPN tests.
TRUE
Describe the membrane filtration technique of finding indicator organisms.
- Detects total coliforms, fecal coliforms and fecal streptococci (derives from intestines of warm-blooded animals)
- Membrane has sample poured on to it and filtered out with vacuum filtration
- Placed on appropriate medium and plates incubated for 24h
- Colonies on filter paper are counted
