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 μg/ml. Chitosan derivatives with the di-quaternary substituents were active against bacteria with MIC as low as 8 μg/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 8× 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.