Lecture 19 Flashcards
What are the methods for differentiating coliform bacteria groups?
Total Coliform Test: Indicates all coliform group bacteria by producing acid and gas at 35–37°C for 48 hours.
Faecal Coliform Test: Detects gas at 44°C after 18–24 hours; better recovery achieved with incubation at 30°C for 4 hours, followed by 14 hours at 44°C. Presumptive faecal coliforms, often confirmed as E. coli.
E. coli Test: Identifies acid (and gas) and indole production at 44°C within 24 hours.
Why are coliforms used as faecal indicator organisms in water and food?
Presence as an Indicator: Coliforms indicate faecal pollution in water and food.
Significance in Water: Coliforms are more reliable as water indicators since they don’t grow in water.
Standards: Coliform presence is a stronger indicator in water than food, as food coliforms can proliferate before analysis.
Faecal Origin: All coliforms are assumed to be of faecal origin until proven otherwise.
What are the limitations of using coliforms as faecal indicator organisms?
No guarantee of pathogens: Coliforms don’t guarantee pathogens are present.
Faster Die-off: Coliforms die off faster than some pathogens.
Not reflective of enteric viruses: Coliforms don’t accurately reflect enteric virus concentrations, as they are less resistant than viruses.
Poor survival in freezing: Coliforms and E. coli don’t survive freezing, making them unsuitable for frozen food indicator purposes.
What are the different sources of coliform bacteria?
Primary Source: The intestinal tract of humans and animals.
Abundance in Faeces: Present in large numbers in human faeces, with 10^6–10^9 faecal coliforms per gram.
E. coli as a Faecal Indicator: E. coli is the most common coliform in intestines and is strictly of faecal origin.
Other Coliforms: Non-E. coli coliforms survive better outside the body and are widely distributed in nature (soil, water, etc.).
What are the categories of water and the coliform indicators typically used?
Two Types of Indicators: Faecal indicators (e.g., E. coli) and quality indicators (e.g., Total Viable Count).
Surface Water and Polluted Groundwater: Both faecal and quality indicators are used; E. coli as the faecal indicator, TVC or Total Coliforms as the quality indicator.
Relatively Unpolluted Groundwater: TVC at 37°C and 22°C are used as quality indicators.
Treated Water: Total coliform test used to assess treatment effectiveness, though absence of coliforms doesn’t guarantee absence of viruses/protozoa.
Water in Distribution: Faecal and non-faecal organisms monitored; a faecal indicator is essential for distribution system analysis.
What is the significance and role of ‘faecal coliforms’ in microbiological quality control?
Safety Assessment: Faecal coliforms are used to assess food safety.
Indicators of Pollution: In water, higher faecal coliforms or E. coli counts indicate more pollution.
Water Quality Standards: According to EC Directives, the limit for E. coli is 0 per 100 ml in drinking water.
Chlorination Effectiveness: The presence of any coliform in chlorinated water indicates inadequate chlorination or post-treatment contamination.
Public Health Threat: Faecal coliforms and E. coli are better indicators of public health risks than total coliforms.
