P057 - Broad-spectrum Antimicrobial Efficacy of Chlorhexidine Against 54 Different Clinical and Reference Strains of Blood-stream Infection Causing Pathogens
Purpose: : Chlorhexidine (CHX) is a widely utilized antimicrobial agent in clinical environment. Present study further extends understanding of efficacy of this important agent through determining Minimum Inhibitory and Minimum Bactericidal Concentrations (MIC/MBCs) and Time-to-Kill (TTK) concentrations against 54 different clinical and reference strains of gram positive, gram negative, and fungal pathogens.
Methods: : MIC CHX solutions with concentrations range of 0.03-512µg/mL were prepared. Broth cultures of ten microbial species encompassing 54 different strains were matched to a 0.5 McFarland Standard and diluted to 10^6CFU/ml. Chlorhexidine solution with specific concentration, inoculum, and nutrient broth were mixed in test plates followed by incubating at 35-37oC for 18-24 hours before spectrophotometric analysis. Test controls were utilized to ensure proper microbial growth, sterility and complete solubilization of chlorhexidine. MBC Aliquots from MIC wells were grown for 24-48 hours in nutrient broth or agar at 37oC. Growth was confirmed via colony counting or spectrophotometrically. TTK CHX concentrations two above and below the MBC were incubated with microorganisms at 10^5CFU/ml in nutrient broth at 37oC and 100 rpm. Samples taken from timepoints ranging from 5 minutes to 24 hours were plated on neutralizing agar, and incubated for 24-48 hours at 37oC after which colonies were enumerated.
Results: : CHX MIC and MBC MIC and MBC for Enterococcus faecalis and faecium strains were 0.49 and 16µg/mL respectively. Staphylococcus aureus and epidermidis strains were highly susceptible with MIC and MBC between 0.06 - 8µg/mL. MIC and MBC for Escherichia coli were within 0.5 - 4µg/mL range. MIC and MBC range for Enterobacter cloacae strains were 2 - 8 µg/mL and 4 - 32µg/mL respectively. Acinetobacter baumannii and Pseudomonas aeruginosa strains were less susceptible with MIC of 8 µg/mL and MBC > 125µg/mL. Similarly, MIC and MBC ranges were 1 - 31.25µg/mL and 1 - 128µg/mL respectively for Klebsiella pneumoniae. The MIC and MBC were comparable for Candida albicans. CHX TTK TTK was determined for 27 strains with fastest kill time of as low as 5 minutes and lowest concentration for kill at 1µg/mL depending on test organism. All microorganisms were killed within 24 hours by 16 µg/mL.
Limitations:: CHX was tested at two different laboratories using different methodologies for MIC and MBC determination. TTK was performed by one laboratory, however, TTK values could only be established for 27 out of 54 strains due to unavailability of the remaining strains to that laboratory.
Conclusions: : Chlorhexidine is a broad-spectrum antimicrobial agent that has been used for multitudes of clinical applications. Both the static and cidal action of chlorhexidine driven by its concentration are equally important for effectiveness of the products utilizing this agent. In this study, Chlorhexidine was found to be effective at inhibiting and killing 54 different laboratory reference strains as well as clinical isolates derived from blood, urine, and respiratory cultures. In conclusion, Chlorhexidine is a powerful antimicrobial agent and products containing chlorhexidine should be considered as the standard of care for infection prevention.
