To calculate the CFU/mL based on the given information, follow these steps:

Given:

1. Dilution factor = $1 \times 10^{-4}$
2. Volume plated = $0.400 \, \text{mL}$
3. Colonies counted = 175

Formula:

$\text{CFU/mL} = \frac{\text{Number of colonies}}{\text{Volume plated (mL)}} \times \text{Dilution factor (inverse)}$

Solution:

1. Inverse of the dilution factor: $\text{Inverse of } 1 \times 10^{-4} = 10^{4}$

2. Plugging into the formula: $\text{CFU/mL} = \frac{175}{0.400} \times 10^{4}$

3. Calculation: $\frac{175}{0.400} = 437.5$ $\text{CFU/mL} = 437.5 \times 10^{4} = 4.375 \times 10^{6} \, \text{CFU/mL}$

Final Answer:

The sample has $4.375 \times 10^{6} \, \text{CFU/mL}$.

Would you like a detailed breakdown of the process or have any additional questions?

Related Questions:

1. How does plating volume affect the calculation of CFU/mL?
2. Why is the dilution factor used in microbiological calculations?
3. What are common errors when calculating CFU/mL from colonies?
4. How can you increase accuracy in counting colonies?
5. What are alternative methods to estimate CFU/mL besides plating?

Tip:

Always ensure that your dilution factor and plating volumes are accurately recorded to avoid calculation errors in CFU/mL estimation.