Comparison of methodologies used in assessing the postantibiotic effect

Area of Science:

• Microbiology
• Pharmacology

Background:

• The postantibiotic effect (PAE) is crucial for understanding antibiotic efficacy.
• Accurate measurement of PAE is essential for optimizing antibiotic dosing strategies.
• Escherichia coli is a common bacterial pathogen where meropenem is frequently used.

Purpose of the Study:

• To determine the postantibiotic effect (PAE) of meropenem against reference strains of Escherichia coli.
• To compare different methods for assessing bacterial regrowth after meropenem exposure.
• To evaluate the accuracy of viable counting and bioluminescence in PAE determination.

Main Methods:

• Exposure of Escherichia coli strains (NCTC 4174 and NCTC 12210) to varying concentrations of meropenem (0.1-100 x MIC) for 2 hours.
• Determination of bacterial regrowth using viable counting, bioluminescence, impedance, and morphological techniques.
• Calculation of PAE using different methodologies.

Main Results:

• Bioluminescence consistently yielded higher bacterial counts than viable counting after meropenem exposure.
• Viable counting underestimated bacterial regrowth due to its inability to detect spheroplasts.
• Inaccurate bacterial counts led to falsely low PAE determinations when using viable counting alone or with impedance.

Conclusions:

• Viable counting is inadequate for accurate PAE determination of meropenem in Escherichia coli due to the formation of spheroplasts.
• Bioluminescence offers a more reliable method for quantifying bacterial regrowth and determining PAE.
• Further research is needed to refine PAE measurement techniques for carbapenem antibiotics.