On the influence of the physicochemical characteristics of chitosans prepared from Hermetia illucens and Schistocerca gregaria on antibacterial activity. Application against reference and isolated resistant bacteria

• Antibacterial activity depends on the characteristics of the chitosan and the strain • Chitosan samples with DA≤10%; Mv≥80,000 g/mol are highly effective against bacteria • Fully deacetylated chitosan sample with Mv=100,000g/mol provides the highest inhibition • Chitosan sample (DA=0%) is more effective against resistant bacteria than used antibiotics • Chitosan appears to be a promising alternative to conventional antibiotics Chitosans with controlled physicochemical properties were prepared from insects Hermetia illucens and Schistocerca gregaria . Chitosans are obtained with molar masses (Mv) ranging from 15,000 to 188,000g/mol, low degree of acetylation (0%≤ DA≤10%) and porous or fibrous surface structure. The antibacterial activity of these chitosans was evaluated against reference and multidrug-resistant bacterial strains using the disk diffusion method after determining the optimal concentrations of acetic acid and chitosan. All prepared chitosans showed inhibition zone diameters ranging from 14 to 18mm, depending on the bacterial strain and the chitosan's properties. When the DA≤10%, chitosans with Mv≥80,000g/mol provide greater antibacterial activity than those with Mv≤20,000g/mol. For comparable Mv, chitosans with low DA exhibit better antibacterial activity than commercial chitosans with DA of 29% to 43%. Fully deacetylated chitosan exhibits the widest zones of inhibition as well as the lowest minimum inhibitory and bactericidal concentrations. The presence of porous surface structure slightly enhanced antibacterial activity against Gram-positive bacteria, whereas no significant effect was observed for Gram-negative bacteria. The antibacterial activity of chitosan with DA=0% and Mv=100,000g/mol was compared to that of antibiotics gentamicin and ciprofloxacin. A 21% improvement was observed against Enterococcus faecalis compared to gentamicin while for other reference strains, this chitosan provided 68% to 86% of the activity of gentamicin and 49% to 80% of that of ciprofloxacin. For isolated resistant bacteria, the improvement compared to gentamicin was 29% to 54%. For ciprofloxacin, to which Acinetobacter baumannii and Klebsiella pneumoniae are resistant, this chitosan shows inhibition zones of 17mm. These results suggest that chitosan is an effective antibacterial agent.