A flow-cytometric gram-staining technique for milk-associated bacteria.

Area of Science:

• Microbiology
• Analytical Chemistry
• Biotechnology

Background:

• Traditional Gram staining is crucial for bacterial identification.
• Flow cytometry offers rapid, high-throughput analysis.
• Combining these methods can enhance bacterial detection.

Purpose of the Study:

• To develop and validate a novel Gram-staining technique using fluorescent dyes for flow cytometry.
• To assess the accuracy of this method in differentiating gram-positive and gram-negative bacteria.
• To evaluate the method's applicability to raw milk analysis.

Main Methods:

• A dual-staining approach using Oregon Green-conjugated wheat germ agglutinin (WGA) for gram-positive bacteria and hexidium iodide (HI) for all bacteria.
• Flow cytometry for detection and quantification of stained bacterial populations.
• Optimization of staining conditions, including potassium chloride concentration and incubation parameters.

Main Results:

• The optimized method achieved high accuracy (average 99%) in differentiating gram-positive and gram-negative bacteria from pure cultures.
• The technique demonstrated robustness across different bacterial growth phases and short-term storage conditions (freezing).
• Accurate analysis of spiked milk samples (Staphylococcus aureus, Escherichia coli) was achieved without precultivation.

Conclusions:

• The developed Gram-staining flow cytometry method provides a reliable and efficient tool for bacterial classification.
• This technique is suitable for rapid analysis of bacterial populations in complex matrices like bulk tank milk.
• It offers a potential advancement for microbial quality control in the dairy industry.