A Coulter counter is a(n):
a. Statistical estimation using 15 dilution tubes and a table of numbers to estimate the number of bacteria per milliliter
b. Indirect method of counting microorganisms
c. Device that directly counts microbes as they pass through a tube in front of an electronic detector
d. Device that directly counts microbes that are differentially stained with fluorescent dyes

Verified step by step guidance

1. Step 1: Understand the principle behind each option. Option (a) describes a statistical estimation method involving dilution tubes, which is typically the Most Probable Number (MPN) method, not a Coulter counter.
2. Step 2: Recognize that option (b) refers to an indirect counting method, which usually involves measuring turbidity or metabolic activity, not direct counting.
3. Step 3: Note that option (c) describes a device that directly counts microbes as they pass through a tube in front of an electronic detector. This matches the principle of a Coulter counter, which detects changes in electrical resistance caused by particles passing through an aperture.
4. Step 4: Option (d) mentions counting microbes stained with fluorescent dyes, which is characteristic of flow cytometry, not a Coulter counter.
5. Step 5: Conclude that the Coulter counter is best described by option (c), a device that directly counts microbes as they pass through a tube in front of an electronic detector.

Key Concepts

Coulter Counter Functionality

A Coulter counter is an electronic device that directly counts particles, such as microbes, by detecting changes in electrical resistance as they pass through a small aperture. It provides rapid and accurate counts without relying on staining or indirect estimation methods.

Direct vs. Indirect Microbial Counting Methods

Direct counting methods involve physically counting individual cells or particles, often using devices or microscopy, while indirect methods estimate microbial numbers based on growth, turbidity, or statistical models. Understanding this distinction helps identify the nature of the Coulter counter.

Microbial Staining Techniques

Staining microbes with fluorescent dyes allows for differentiation and counting under specialized microscopes, such as fluorescence microscopes. This method is distinct from Coulter counting, which does not require staining but relies on electrical detection.