Single-cell detection: test of microbial contamination using capillary electrophoresis

Area of Science:

• Analytical Chemistry
• Microbiology
• Biotechnology

Background:

• Capillary electrophoresis (CE) is used for microbial contamination detection.
• Previous methods using nutrient broth as a blocking agent were limited to detecting ~50 cells.
• High background fluorescence from nutrient broth hindered sensitive detection.

Purpose of the Study:

• To enhance the sensitivity of CE-based microbial detection down to single-cell levels.
• To identify and evaluate alternative synthetic blocking agents to replace nutrient broth.

Main Methods:

• Screening of various synthetic compounds (salts, polypeptides, zwitterions, surfactants) as blocking agents.
• Utilizing a dilute cationic surfactant buffer and a blocking agent plug in CE.
• Evaluating blocking agent performance based on cellular aggregation, mobility, and background fluorescence.

Main Results:

• Zwitterionic surfactants effectively mimic nutrient broth's effects on microbial cells.
• Caprylyl sulfobetaine significantly reduced blocker plug fluorescence by up to 40x.
• This reduction enabled single-cell detection with signal-to-noise ratios of 5-9.

Conclusions:

• Synthetic blocking agents, particularly caprylyl sulfobetaine, dramatically improve CE sensitivity for microbial detection.
• The enhanced CE technique allows for single microorganism detection.
• This method shows potential as a rapid sterility testing tool.