Chitosan biological molecule improves bactericidal competence of ceftazidime against Burkholderia pseudomallei biofilms

Biofilm-associated Burkholderia pseudomallei infections (melioidosis) are problematic because of reduced sensitivity to antibiotics and high frequency of relapse. Biofilm dispersal agents are essential to liberate the biofilmencased cells, which then become planktonic and are more susceptible to antibiotics. This study aimed to evaluate the ability of deacetylated chitosan (dCS), an antimicrobial and antibiofilm biological macromolecule, to disrupt established biofilms, thus enabling ceftazidime (CAZ) to kill biofilm-embedded B. pseudomallei. We combined dCS with CAZ using a mechanical stirring method to generate dCS/CAZ. In combination, 1.25-2.5 mg ml(-1) dCS/1-2 mu g ml(-1) CAZ acted synergistically to kill cells more effectively than did either dCS or CAZ alone. Notably, a combination of 5-10 mg ml(-1) dCS with 256-512 mu g ml(-1 )CAZ, prepared either by mechanical stirring (dCS/CAZ) or mixing (dCS + CAZ), drastically improved bactericidal activities against biofilm cells leading to a 3-6 log CFU reduction. Confocal laser-scanning microscope (CLSM) images revealed that 10 mg ml(-1) dCS/512 mu g ml(-1) CAZ is by far the best formulation to diminish B. pseudomallei biofilm biomass and produces the lowest live/dead cell ratios of B. pseudomallei in biofilm matrix. Collectively, these findings emphasize the potential of novel therapeutic antibacterial and antibiofilm agents to fight against antibiotic-tolerant B. pseudomallei biofilmassociated infections.

Automated summary

This study evaluates the ability of deacetylated chitosan (dCS) to disrupt biofilms of Burkholderia pseudomallei, enabling ceftazidime (CAZ) to kill the embedded bacteria. The combination of dCS and CAZ acts synergistically to kill biofilm cells more effectively than either compound alone.