Antimicrobial effect of novel hydrogel matrix based on natural polysaccharide Sterculia urens

Materials for modern wound-management are a very broad and heterogeneous group. One of the most important representatives is natural materials, or more precisely polysaccharides isolated from various plants and animals. With the increasing resistance of pathogens to established antimicrobial agents, there is also an attempt to discover new mechanisms of the effects of these materials. Gum karaya (GK) is a very promising representative of the natural polysaccharides group and, since it is obtained from Sterculia urens as resin, it is also possible to assume its certain antimicrobial activity.

The antimicrobial potential of GK and chitosan (Ch) has been tested on several preselected strains to match the real epidemiological situation of the agents of infectious complications in the field of burned wounds. Tested strains included representatives of gram-positive and gram-negative bacteria as well as selected yeasts. Methicillin susceptible Staphylococcus aureus CCM 4223 (ATCC 29213), methicillin resistant Staphylococcus aureus CCM 4750 (ATCC 43300), Klebsiella pneumoniae CCM 4985 (ATCC 700603), Candida albicans CCM 8261 (ATCC 90028), Pseudomonas aeruginosa CCM 3955 (ATCC 27853) were obtained from the Czech Collection of Microorganisms. Pseudomonas aeruginosa FF 1, Pseudomonas aeruginosa FF 2 and Pseudomonas aeruginosa FF 3 (all multi-resistant clinical strains), Staphylococcus epidermidis A 013, Staphylococcus epidermidis A 117, and Candida parapsilosis BC 11 were obtained from the Collection of Microorganisms at the St. Annes University Hospital, Brno. Antimicrobial tests were performed using the disk diffusion test methodology. Another set of antimicrobial tests was obtained by measuring the growth curves.

Bacteriostatic activity testing showed 1% GK concentration and both 1% and 0.5% chitosan concentration effective against all pathogens tested. The combination of GK50/Ch50 in concentrations of 1% and 0.5% had similar or better effect. Lower concentrations of the combined material are poorly effective against tested strains. Bactericidal activity testing has not produced positive results, except for Candida spp., where only a partial effect of GK50/Ch50 was observed at 1% concentration. In the growth curve test, the efficiency of both GK alone and chitosan was found to be significantly higher in gram-positive bacteria compared to gram-negative ones. In the case of this experiment, only a one-tenth concentration was used compared to the disk diffusion test concentration. This results correspond with the data from the bacteriostatic activity testing.

This is the first publication that attempts to comprehensively define the potential for GK antimicrobial activity and also the possible potentiation of this activity with the use of chitosan. Further experiments are needed to extend the antimicrobial efficiency to gram-negative bacteria.