11:680:390 Lecture Notes - Lecture 24: Macconkey Agar, Norovirus, Coliform Bacteria
26 Apr 2018
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Department
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24: Food and Water
I. Waterborne Diseases
A. Agents and Sources
1. Potable water used for drinking and cooking (undergoes extensive
treatment including filtration and chlorination)
2. Recreational water from public ponds, lakes, swimming pools, etc.
B. Public Health and Water Quality
1. Potable and recreational water are routinely tested for specific indicator
organisms
(signals potential for disease)
2. Coliform - contamination associated with fecal matter
a) Gram negative organisms
b) Facultative aerobe that ferments lactose with gas formation within
48 hours at 35oC
c) Not all coliforms are fecal, but most are.
3. Testing for coliforms
a) MacConkey Agar - differential (pH indicator) and naturally
selective for gram-negative organisms
b) MPN - most-probably-number procedure
c) Membrane filter (MF) procedure
C. Legionellosis
1. Caused by Legionella pneumoniae
2. Epidemiology
a) Common in cooling towers and evaporative condensers of large
air condition systems; also found in water towers
(1) The pathogen grows in the water and is disseminated in
humidified aerosols
(2) Relatively resistant to heating and chlorination
b) Infection is NOT spread from person to person = affects alveoli in
lungs (deeper in the cavity), so you cant cough it up. Mostly just
spread through water
3. Treatment: antibiotics
D. Norovirus Illness
1. Norovirus (Norwalk Agent) is a common gastrointestinal illness; very
contagious; known to cause projectile vomiting, diarrhea, & fatigue
2. Noroviruses are transmitted by fecal-oral route. Most cases are traced in
contaminated drinking or recreational water
3. Viruses can survive in water for long periods but are inactivated by
disinfection with chlorine
II. Foodborne Diseases
A. Food Spoilage
1. Perishable foods typically have higher moisture content and must be
stored in conditions to limit microbial growth
