Antimicrobial activity of piperazine derivatives of chitosan

Well characterized methylpiperazine, mono-quaternary dimethylpiperazine and di-quaternary trimethylpiperazine derivatives of chitosan, with different degrees of substitution, were investigated for antibacterial activity against five strains of Gram-positive and Gram-negative bacteria. Some of the methylpiperazine and the dimethyl piperazine derivatives of chitosan, with low degree of substitution, were active against bacteria at pH 5.5 with minimum inhibitory concentration (MIC) >= 64 mu g/ml. Chitosan derivatives with the di-quaternary substituents were active against bacteria with MIC as low as 8 mu g/ ml and in general more active at pH 7.2 than at pH 5.5. The minimum lethal concentrations (MLC) were the same as the MIC within 1-2 dilutions. The most active compound induced gradual decrease in the count of viable bacteria over 8 h at 8x MIC. The results are consistent with the interpretation that methylpiperazine and mono-quaternary dimethylpiperazine substituents do not contribute to activity against bacteria, whereas di-quaternary trimethylpiperazine moiety. will contribute to antibacterial activity. (C) 2008 Elsevier Ltd. All rights reserved.