Question 1

Which of the following characteristics is used to identify coliform bacteria in water testing?

Accepted Answer

Fermentation of lactose with acid and gas production

Question 2

Why is Escherichia coli considered a reliable indicator of fecal contamination in water?

Accepted Answer

It is commonly found in the intestines and can survive outside the body for extended periods

Question 3

A water sample is tested using the presumptive test. What result would indicate the possible presence of coliforms?

Accepted Answer

Yellow color and gas production in the Durham tube

Question 4

What is the main purpose of using eosin methylene blue (EMB) agar in the confirmed test for coliforms?

Accepted Answer

To differentiate between lactose fermenters and non-fermenters among Gram negative bacteria

Question 5

Which of the following best describes the appearance of Escherichia coli colonies on EMB agar?

Accepted Answer

Green metallic sheen

Question 6

If a water sample contains more than 2.2 coliforms per 100 mL, what does this indicate?

Accepted Answer

The water is contaminated with fecal material and unsafe for drinking

Question 7

Which two by-products are detected in the presumptive test for coliforms using phenol red and a Durham tube?

Accepted Answer

Acid and gas

Question 8

A completed test for coliforms involves which of the following steps?

Accepted Answer

Gram staining to confirm Gram negative rods

Question 9

Which of the following diseases is NOT typically associated with contaminated drinking water?

Accepted Answer

Tuberculosis

Question 10

Why is direct testing for pathogens such as Salmonella typhi in water samples considered impractical?

Accepted Answer

Pathogens are usually present in very low numbers, making detection difficult

Question 11

Which of the following best describes the membrane filter technique for water analysis?

Accepted Answer

It traps bacteria on a filter, which is then placed on differential media for colony counting

Question 12

A student streaks a water sample on EMB agar and observes colorless colonies. What does this indicate?

Accepted Answer

Presence of lactose non-fermenting Gram negative bacteria

Question 13

Which of the following is NOT a characteristic of coliform bacteria?

Accepted Answer

Gram positive cocci

Question 14

During the Most Probable Number (MPN) test, which step provides an indirect estimate of coliform bacteria in a water sample?

Accepted Answer

Presumptive test using lactose broth

Question 15

Which of the following best explains why coliforms are used as indicators of fecal contamination?

Accepted Answer

They are present in the intestines of humans and animals and survive well outside the body

Question 16

A water sample is tested and found to have colonies with a green metallic sheen on EMB agar. What is the most likely organism present?

Accepted Answer

Escherichia coli

Question 17

Which of the following steps is NOT part of the standard coliform testing sequence?

Accepted Answer

Catalase test

Question 18

A public health laboratory receives a water sample and performs the MPN test. The results show positive lactose fermentation in all 10 mL tubes, some 1 mL tubes, and no 0.1 mL tubes. What is the next step?

Accepted Answer

Perform a confirmed test by streaking EMB plates

Question 19

Which of the following best describes the fecal-oral route of transmission?

Accepted Answer

Pathogens are transmitted from feces to mouth, often via contaminated water or food

Question 20

Which of the following is a key reason why pathogens are not directly tested for in routine water analysis?

Accepted Answer

They are difficult to culture and usually present in low numbers

Microbiological Analysis of Drinking Water: Detection of Coliforms and Waterborne Pathogens

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