Can we fight Salmonella with nano chitosan?

Salmonellosis in animals refers to diseases caused by Gram-negative bacteria from the Enterobacteriaceae, specifically Salmonella enterica. Of about 2500 serotypes of this species, about 10% are isolated from poultry. Special significance of salmonella comes from their character, as some serotypes can endanger human health leading to gastrointestinal toxin infections due to the consumption of poultry products. Chitosan is a linear positively charged polyaminosaccharide (2-amino-2-deoxy-(1→ 4)-β-D glucosamine) obtained by partial deacetylation of chitin, which is a structural component with a protective function of arthropods, fungi, lichens, and bacteria. It is cost effective, non-toxic, biodegradable, has good absorptivity, non-hypersensitivity and biocompatible natural polymer. In the nanoform chitosan is stable at high temperature and resistant to microbial and enzymatic degradation at neutral pH, while retaining its positively charged amino groups responsible for its antibacterial activity. The proposed mechanism of antibacterial interaction involves positively charged chitosan interacting with negatively-charged microbial cytoplasmic membrane residues (proteins, lipids, and carbohydrates) blocking its permeability and culminating in the leakage of cytoplasmic contents. Since eukaryotic cells have a different organization, chitosan (as polymer or in form of nanoparticles) and chitosan-based composites are non-toxic for animal or human tissues. Promising results were observed with chitosan-based materials intended for use in sites with a heavy bacterial burden such as cecum. Antimicrobial tests were conducted on hydrogel based disks with chitosan, testing their effectiveness against planktonic cells and biofilms. For antimicrobial activity, ISO 20776-1 modified in placing discs instead of antibiotics, was used. Bactericidal concentrations (BCs) were determined after IC in subsequent sub-cultivation of 10 µl of broth from wells without growth (i.e. obvious button or definite turbidity) to MHA. Following promising results with several type strains, such as S. aureus, Methicillin resistant S. aureus, E. coli, K. pneumoniae, P. mirabilis, S. Infantis, S. Typhimurium, and P. aeruginosa, antibacterial tests were conducted on 20 isolates of variety local isolated Salmonella including: S. Enteritidis, S. Infantis, S. Mbandaka, S. Senftenberg, S. Typhimurium, S. Agona, S. Taksony and S. Tshiongwe. Tested samples revealed some level of inhibitory effect of chitosan-based material in 85% of tested salmonella, but visually undetected growth was in 35%. A bactericidal effect was noticed in 15% of isolates. The results reveal some kind of indicative results that hydrogel-based disks with chitosan could have a very good activity against salmonella. The nanoform of chitosan hydrogels synthesis is a complex procedure which allows further engineering modification in several steps. Further work and testing are required to achieve better antimicrobial effect