Heterotrophic plate counts of surface water samples by using impedance methods

Area of Science:

• Microbiology
• Environmental Science
• Analytical Chemistry

Background:

• Conventional methods like spread plating for heterotrophic plate counts (HPC) are time-consuming.
• Impedance methods offer potential for rapid bacterial enumeration in water samples.

Purpose of the Study:

• To evaluate impedance methods as a viable alternative to conventional techniques for HPC determination.
• To compare the performance of capacitance and conductance impedance measurements.
• To assess the influence of incubation temperature and media on impedance-based HPC estimations.

Main Methods:

• Investigated impedance methods (capacitance and conductance) as alternatives to membrane filtration, spread plating, and pour plating.
• Compared impedance detection times with conventional HPC results across various water samples.
• Analyzed the effect of incubation temperatures (≤25°C and ≥30°C) on regression models.
• Compared broth-based R2A medium and plate count agar performance.

Main Results:

• Capacitance-based impedance measurements yielded faster detection times than conductance.
• Highest correlation (r=0.966) between HPC and detection time was achieved using capacitance.
• Incubation temperature significantly affected regression models; optimal correlations (R²=0.878-0.933) were observed at ≤25°C.
• Plate count agar incubated at 25°C with capacitance signal showed high correlation (r=0.966) with HPC.

Conclusions:

• Impedance methods, particularly using capacitance, are a suitable and rapid alternative for HPC determination in water.
• Optimal performance requires careful consideration of incubation temperature and specific media choices.
• This technique reduces analysis time compared to traditional plating methods.