Chlorhexidine is a disinfectant which is effective against a wide range of vegetative Gram positive and Gram-negative bacteria. It is ineffective against acid-fast bacteria, bacterial spores, fungi and viruses. It is more active against Gram-positive than Gram-negative bacteria, and some species of Pseudomonas and Proteus are relatively less susceptible. Chlorhexidine is most active at a neutral or slightly alkaline pH and its activity is reduced by blood and other organic matter.