NEUTRALIZATION OF CHLORHEXIDINE FOR IN-VI TRO TESTING OF DISINFECTANTS

An insufficient neutralization of chlorhexidine (4%), tested in vitro against Enterococcus faecium ATCC 6057, was suspected in the quantitat ive suspension test although the combination Tween 80, cysteine, histi dine and saponine was assessed as sufficient for neutralising chlorhex idine. Bactericidal activity of each neutralising compound and their c ombinations was excluded. Sufficient neutralization was observed when all dilution steps and the corresponding agar plates were supplemented with the neutralising compounds. Successful neutralization in broth i s not equivalent with successful neutralization in tryptic saline. We suggest to supplement at least the agar plates of the first dilution s tep with neutralising compounds when testing chlorhexidine.