Water Purity and Microbial Contamination

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Questions and Answers

What effect does a heavy inoculum have on the production of the metallic sheen?

It has no effect on the sheen.

It causes a color change in colonies.

It enhances the production of the sheen.

It suppresses the production of the sheen. (correct)

What does the presence of both fecal coliforms and fecal streptococci indicate?

Low levels of coliforms.

Presence of fecal contamination. (correct)

Contamination from food sources.

Absence of fecal contamination.

Which method is used to determine the number of coliforms in a volume of water?

M-Endo agar plate. (correct)

Drop plate technique.

Spread plate technique. (correct)

Streak plate technique.

What is the purpose of the FC/FS ratio in public health?

To identify the type of contamination source. Signup and view all the answers

What is a necessary step before using the glass spreader in the spread plate technique?

Sterilize it by passing through the flame. Signup and view all the answers

What is the primary reason for diluting the broth culture before performing the spread plate technique?

To prevent overcrowding of colonies. Signup and view all the answers

What type of pollution has historically raised the most concern regarding water purity?

Microbial pollution Signup and view all the answers

What is the primary route through which diseases from contaminated water are transmitted?

Fecal-oral route Signup and view all the answers

Which organism is commonly used as an indicator of potential water contamination?

Escherichia coli Signup and view all the answers

Why is it impractical to identify every pathogen in a contaminated water sample?

Pathogens are usually present in low numbers. Signup and view all the answers

What do coliform bacteria primarily indicate in a water sample?

Fecal contamination Signup and view all the answers

How are coliform bacteria characterized?

They ferment lactose with acid and gas formation. Signup and view all the answers

What potential risk arises from using contaminated water for irrigation?

Contaminated produce Signup and view all the answers

Which genus does Escherichia belong to?

Enterobacteriaceae Signup and view all the answers

What is a key reason for testing water for only a few specific organisms rather than all pathogens?

It saves time and resources. Signup and view all the answers

What is the maximum number of coliforms allowed in a 100 ml sample of drinking water?

One coliform Signup and view all the answers

Which method is widely used for sampling coliforms in water?

Membrane filter technique Signup and view all the answers

What is the purpose of including sodium lauryl sulfate in the m-Endo medium?

To inhibit gram-positive organisms Signup and view all the answers

What appearance do lactose-fermenting coliforms exhibit on m-Endo medium?

Red color with a metallic sheen Signup and view all the answers

What role does lactose play in the detection of coliforms in water samples?

It differentiates between coliforms and noncoliforms Signup and view all the answers

During the membrane filter technique, what happens to the bacteria retained on the filter?

They are incubated and form colonies Signup and view all the answers

What is the action limit for coliforms in drinking water that triggers necessary action?

Four coliforms Signup and view all the answers

What is the primary advantage of the membrane filter technique in water sampling?

It provides results in a short period of time Signup and view all the answers

Which component of m-Endo medium serves as the pH indicator?

Basic fuchsin Signup and view all the answers

What is the purpose of sodium sulfite in the m-Endo medium?

To decolorize basic fuchsin Signup and view all the answers

Study Notes

Water Purity and Microbiological Contamination

Pure water does not exist naturally.
Water pollution is a significant environmental issue due to chemical and microbiological contaminants.
Microbial contamination is a major concern for water purity because it can transmit diseases like dysentery, typhoid fever, and cholera through contaminated water sources.
Contaminated irrigation water can lead to produce contamination, resulting in human and animal disease.

Detection of Microorganisms in Water

It is impractical to identify every organism in a water sample.
Pathogen numbers are typically low in water, making them difficult to detect during routine testing.
By the time individual pathogens are identified, it may be too late to prevent their spread.
Water samples are examined for a limited number of indicator organisms to suggest the presence of potentially pathogenic fecal organisms.

E. coli as an Indicator Organism

Escherichia coli (E. coli) is a common indicator organism found in the intestinal tracts of humans and animals.
Its presence signifies potential fecal contamination and an increased risk of other pathogenic organisms.
Any member of the coliform bacteria (Enterobacteriaceae) family, which are characterized by their ability to ferment lactose with acid and gas production, can serve as indicator organisms.
Coliforms include genera like Enterobacter, Klebsiella, Citrobacter, and Escherichia.
A significant number of coliforms in a water sample indicates fecal contamination, potentially making the water unsafe for drinking or recreational purposes.

Public Health Standards for Water Quality

Public health standards set maximum coliform limits based on water usage.
Drinking water has a strict limit of one coliform per 100 ml of water, with an action limit of four coliforms per 100 ml.
Water for recreation, irrigation, and discharge into bays or rivers has higher allowable limits.

Membrane Filter Technique

The membrane filter method is commonly used to determine coliform counts in water.
It provides results quickly, allowing the processing of large water volumes while maintaining high reproducibility.
The method involves filtering water through a nitrocellulose acetate or polycarbonate filter that retains particles, including bacteria, larger than 0.45 micrometers.
The filter is incubated on a nutrient pad, allowing bacteria to grow into visible colonies.
By counting colonies and calculating CFU/ml, the number of bacteria in the water sample can be determined.

Nutrient Pads and Media

Nutrient pads used in the membrane filter technique are selective and differential media to encourage the growth of specific organisms while inhibiting others.
m-Endo medium is a selective and differential medium commonly used for coliform detection.
It inhibits the growth of gram-positive organisms and differentiates between coliforms and non-coliforms based on lactose fermentation, resulting in distinctive colony appearances (red with a metallic sheen for coliforms).

KF Streptococcus Agar

KF Streptococcus agar is another type of nutrient pad used to detect fecal streptococci, which are also indicative of fecal contamination.
The FC/FS ratio (number of fecal coliforms divided by the number of fecal streptococci) can help determine the source of fecal contamination:
- Human fecal contamination: Higher fecal coliform count than fecal streptococci count.
- Animal fecal contamination: Higher fecal streptococci count than fecal coliform count.

Spread Plate Technique

The spread plate technique is another method for determining coliform counts and obtaining isolated colonies.
It involves spreading a diluted broth culture of microbes evenly on the surface of an agar medium.
A sterilized glass spreader or hockey stick is used to spread the culture.
Single colonies can be picked and grown in broth to generate a pure culture.
The spread plate technique can be used to estimate the total number of bacteria in a broth culture.

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Description

Explore the critical issues surrounding water purity and the dangers of microbial contamination. This quiz delves into the detection of microorganisms, the significance of E. coli as an indicator, and the implications of contaminated water sources. Test your knowledge on the topics that affect water quality and public health.