Chitosan as an effective inhibitor of multidrug resistant acinetobacter baumannii

Background: Acinetobacter baumannii is a multidrug resistant pathogen often associated with nosocomial outbreaks, with an innate ability to evade nearly all traditional antibiotics and a capacity to adhere and colonize medical devices. Chitosan is a biocompatible and non-toxic polymer which has been shown to have a strong antimicrobial activity against antibiotic resistant microorganisms, with potential to become an alternative to traditional antimicrobials. Method: Chitosan’s biological activity was assessed upon two A. baumannii strains (one clinical multidrug resistant strain (MDR) and one reference strain CCUG 61012) in planktonic and sessile environments. From a planktonic standpoint minimal inhibitory concentration (MIC) and the minimal bactericidal concentrations (MBC) were determined while from a sessile perspective minimal biofilm inhibitory concentration (MBIC), adhesion and biofilm formation were assayed through biomass and metabolic activity inhibition. Results & Conclusions: Results showed that the chitosan molecular weights tested were effective in inhibiting A. baumannii’s planktonic and sessile growth. For the first MICs and MBCs were obtained at relatively low concentrations (0.5–2 mg/mL). For the latter, MBICs varied between 1 and 8 mg/mL and chitosan effectively inhibited both A. baumannii’s adhesion and biofilm formation, with this inhibitory activity being more pronounced from a biomass formation standpoint. Analyzing the differences observed between the reference and the MDR A. baumannii’s strains, the MDR strain was, in general, as susceptible as the reference strain to chitosan’s activity. Overall, chitosan showed high potential as a possible natural alternative to the treatment of multidrug resistant A. baumannii infections with the high antibiotic resistance profile of this microorganism not being an impediment to chitosan’s activity both in planktonic and sessile settings.