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Direct Methods of Bacterial Enumeration

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Questions and Answers

What is the main limitation of the microscopic cell count method in bacterial enumeration?

Presence of overlapping cells in high-density samples

Difficulty in distinguishing between viable and non-viable cells (correct)

Inability to calculate cell density accurately

Problems with motile cells moving between grid squares

What is the purpose of using a Petroff-Hausser counting chamber in the microscopic cell count method?

To differentiate between Gram-positive and Gram-negative bacteria

To calculate the volume of the bacterial suspension

To count cells per unit area for calculating overall concentration (correct)

To identify the bacteria species present in the culture

Why is it necessary to perform serial dilution on a bacterial broth culture before obtaining a countable number of viable bacteria?

To avoid interference from non-bacterial contaminants

To ensure uniform distribution of bacterial cells in the culture

To reduce the initial high cell density to a manageable range (correct)

To prevent overestimation of the total cell count

What does a single, well-isolated colony on an agar plate represent in terms of bacterial replication?

The outcome of a single cell replicating at that location Signup and view all the answers

What potential issue arises when motile cells are counted using the microscopic cell count method?

Double counting due to their movement across grid squares Signup and view all the answers

What is the purpose of serial dilution in bacterial culture?

To decrease the concentration of the bacterial broth culture Signup and view all the answers

What is the significance of subculturing/aliquoting after serial dilution?

To create multiple colonies from one viable bacterial cell Signup and view all the answers

Why is the drop plate method preferred over the spread plate method for bacterial enumeration?

It uses less media Signup and view all the answers

Which direct method of bacterial enumeration is best suited for samples with low microbial concentrations like wastewater?

Filtration method Signup and view all the answers

In the pour-plate method, why is sterile medium added after pipetting the diluted culture onto a sterile plate?

To promote surface colony formation Signup and view all the answers