Development of a Broth Microdilution Method To Characterize Chlorhexidine MICs among Bacteria Collected from 2005 to...

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Chlorhexidine (CHX) bathing is widely used in U.S. hospitals to prevent the spread of multidrug-resistant organisms (MDROs).
• Increasing CHX use raises concerns about the potential emergence of bacterial resistance to this critical antiseptic agent.
• There is a lack of standardized methods to evaluate CHX susceptibility in clinical isolates.

Purpose of the Study:

• To establish a reliable broth microdilution method for determining CHX minimum inhibitory concentrations (MICs).
• To evaluate the current CHX MICs for common healthcare-associated pathogens.
• To provide a tool for monitoring potential increases in CHX resistance.

Main Methods:

• Adapted a standard broth microdilution technique for CHX MIC determination.
• Prepared and validated MIC testing panels with quality control ranges.
• Tested clinical isolates of *Staphylococcus aureus*, *Escherichia coli*, *Klebsiella pneumoniae*, and *Enterobacter cloacae* complex from three U.S. sites.

Main Results:

• Successfully adapted and validated a reproducible broth microdilution method for CHX MIC testing.
• Determined CHX MIC distributions for 535 isolates across four key bacterial species.
• Observed a wide range of MICs, with notable higher MICs for *K. pneumoniae* and *E. cloacae* complex.

Conclusions:

• The developed broth microdilution method is suitable for multi-laboratory use to determine bacterial CHX MICs.
• This method provides a crucial capability for investigating potential increases in CHX resistance.
• Monitoring CHX susceptibility is essential to ensure the continued effectiveness of CHX in healthcare settings.