Chlorhexidine susceptibility and Eagle effect in planktonic cells and biofilm of nosocomial isolates

Abstract

The aim of this study is to evaluate the chlorhexidine gluconate (CHG) susceptibility in both planktonic cells and biofilm of 32 Gram-negative (Gn) and 6 Gram-positive (Gp) isolates by minimal inhibitory concentration (2-256μg/mL for Gn and 2-32μg/mL for Gp), minimal bactericidal concentration (4-256μg/mL for Gn and 2-32μg/mL for Gp) in planktonic cells, and minimal biofilm elimination concentration (128 ≥ 16,384μg/mL in Gn and 32 ≥ 16,384μg/mL in Gp) in biofilm environment. Our study showed that Gn isolates have higher minimal concentrations than Gp and bacteria in biofilms are more tolerant than planktonic ones. No correlation between MBC or MBEC and biofilm formation was statistically confirmed. The Eagle effect, previously described for antimicrobials and antifungals, was evidenced in this work for CHG, an antiseptic. Besides that, the phenomenon was described in 23/38 isolates (60.5%), raising minimal concentration up to ≥ 16,384μg/mL. Our study showed that clinical isolates have a high ability to form biofilm allowing them to tolerate CHG concentrations as high as the ones used in clinical practice. Therefore, attention should be given to the occurrence of this phenomenon to avoid false susceptibility results.