A fluorescent Gram stain for flow cytometry and epifluorescence microscopy

Area of Science:

• Microbiology
• Biotechnology
• Analytical Chemistry

Background:

• Traditional Gram staining is crucial for bacterial identification but has limitations with unfixed samples and certain species.
• Existing methods may struggle with gram-variable or anaerobic bacteria, leading to misclassification.
• Need for improved, rapid diagnostic techniques in microbiology.

Purpose of the Study:

• To develop and validate a new fluorescent staining technique for bacterial Gram differentiation.
• To assess the efficacy of combining hexidium iodide (HI) and SYTO 13 dyes.
• To evaluate the method's performance on various bacterial types, including gram-variable and anaerobic organisms.

Main Methods:

• Utilized two fluorescent nucleic acid binding dyes: hexidium iodide (HI) and SYTO 13.
• Applied the dyes in combination to unfixed bacterial suspensions.
• Observed differential fluorescence: HI (red-orange) for gram-positive, SYTO 13 (green) for gram-negative.

Main Results:

• HI selectively stained gram-positive bacteria, while SYTO 13 stained both gram-positive and gram-negative.
• Combined staining resulted in distinct red-orange fluorescence for gram-positive and green for gram-negative organisms.
• Accurate Gram status prediction for 45 clinically relevant strains, including gram-variable and anaerobic bacteria.

Conclusions:

• The combined HI and SYTO 13 fluorescent staining method offers a reliable alternative to traditional Gram staining.
• This technique provides rapid and accurate differentiation of bacteria in suspension, even for difficult-to-classify species.
• Potential for application in clinical diagnostics and microbial research.