A water sample is considered satisfactory by a presumptive coliform count when the count is atleast
**Core Concept**
The presumptive coliform count is a method used to detect the presence of coliform bacteria in water samples. This test is based on the principle that coliform bacteria ferment lactose in the presence of bile salts, producing gas and causing the medium to become turbid.
**Why the Correct Answer is Right**
The correct answer is based on the standard guidelines for water quality testing. According to the World Health Organization (WHO) and the US Environmental Protection Agency (EPA), a water sample is considered satisfactory if it has a coliform count of 0 colonies per 100 mL. This indicates that the water is safe for consumption. The presence of coliform bacteria in water can indicate contamination with human or animal waste, posing a risk to public health.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a count of 1-9 colonies per 100 mL is considered a marginal or intermediate result, indicating possible contamination. It is not a satisfactory result.
**Option B:** This option is incorrect because a count of 10-99 colonies per 100 mL is considered a positive result, indicating contamination. It is not a satisfactory result.
**Option C:** This option is incorrect because a count of 100 colonies per 100 mL or more is considered a high positive result, indicating severe contamination. It is not a satisfactory result.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the presumptive coliform count is a screening test, and a negative result does not guarantee the water is completely safe for consumption. Further testing, such as the confirmed coliform count, is required to confirm the results.
**Correct Answer: A. 0 colonies per 100 mL**