Már Másson, Amin Amani, Vivien Nagy and Sankar Rathinam
Introduction: Chitosan and its derivatives inhibit growth and eliminate pathogenic microorganisms, including bacteria and fungi. While the polymer’s molecular weight (Mw) significantly influences antimicrobial activity, the precise relationship between molecular weight and this activity remains unclear. Our recent work has demonstrated that the efficacy of trimethyl chitosan against S. Aureus rises with Mw up to a critical molecular weight for maximum activity (CMW). Mw did not impact the activity beyond this threshold.
Aim: Drawing inspiration from Kubiniy’s bilinear quantitative structure-activity relationship equations; we formulated a bilinear equation to elucidate the molecular weight-antimicrobial activity with chitosan and its derivatives. In this study, the equation was fitted to literature data.
Method: To encapsulate the bilinear relationship between molecular weight and activity based on the measured minimum inhibitory concentration (MIC) of the polymer, we introduced Equation 1, where three constants govern the shape of the Log (1/MIC) vs. Mw graph. The CMW is the critical molecular weight for maximum activity, Amax (MICmin) represents antimicrobial activity when Mw>CMW, and Amin (MICmax) is the projected activity as Mw approaches zero.
Results: Twenty-nine datasets from studies published between 1984 and 2019, providing MIC values for chitosan and its derivatives relative to MW, were used for the analysis. Excellent conformity in least-squares fitting to the equations was achieved across datasets. For datasets with suitable fits and at least three values on either side of CMW, CMW values ranged from 4 to 10 KD.
Conclusion: The bilinear equation accurately describes the relationship between Mw and antimicrobial activity
