Effect of chitosan molecular weight as micro and nanoparticles on antibacterial activity against some soft rot pathogenic bacteria

• The particle size for CSNPs was found to be correlated with CS's MW.
• MVCN exhibit higher antibacterial activity than MVC against all tested bacteria.
• MWCN showed lower MIC and MBC values compared to MWC only for P. fluorescens.
• LWCN showed lower MIC and MBC values compared to LWC only for E. coli.

This study evaluates the in vitro antibacterial activity of three molecular weights of chitosan in the form of micro (CS) as well as nanoparticles (CSNPs). CSNPs were prepared using low (LWC), medium molecular weight (MWC) and middle-viscous crab shells chitosan (MVC). The antibacterial activities were evaluated through determination of IC50, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Pseudomonas fluorescens, Erwinia carotovora and Escherichia coli. Experimental results showed that the antibacterial activity was significantly enhanced in the CSNPs comparison to CS microparticles, especially so for MVC nanoparticles (MVCN) in that the MIC values against all tested bacteria were ca. 50% those of the microparticles. Moreover, MWC and LWC nanoparticles showed lower MIC values compared with related microparticles only for P. fluorescens and E. coli, respectively. In addition, atomic force microscopy (AFM) of CSNPs-treated cultures of selected bacteria species revealed structural changes in the bacterial cell wall. The present study indicates that the antibacterial activity of CS varied depending on the molecular weight of CS micro and nanoparticles forms as well as on the particular bacterium. The selection of CS's molecular weight could be thought to be more dependent on its application.