New rapid technique for counting microorganisms directly on membrane filters

Area of Science:

• Microbiology
• Analytical Chemistry

Background:

• Direct counting of microorganisms on membrane filters is a standard microbiological technique.
• Classical methods can be limited by filter background interference and staining efficacy.

Purpose of the Study:

• To present a modified technique for enhanced direct microorganism enumeration on membrane filters.
• To evaluate the effectiveness of different clearing agents and stains.
• To identify optimal filter types for improved microbial contrast.

Main Methods:

• The technique involves clearing membrane filters with immersion oil, paraffin oil, or cedar oil.
• Filters were subsequently stained using crystal violet, carbol fuchsin, or malachite green.
• Comparison of various filter types, including Millipore (0.1 micron pore size, VC type), was conducted.

Main Results:

• Clearing the filter with oil prior to staining significantly improved the visibility of microorganisms.
• Millipore filters (0.1 micron pore size, VC type) demonstrated superior contrast between the microorganisms and the filter surface compared to other tested filters.
• The combination of oil clearing and specific stains enhanced the accuracy of direct microbial counts.

Conclusions:

• The modified technique offers a more effective and reliable method for direct microorganism counting on membrane filters.
• The use of oil clearing agents and appropriate filter selection, such as Millipore VC type, is crucial for maximizing contrast and accuracy.
• This improved method has implications for microbial quality control and research applications.