Virulence factors of Acinetobacter baumannii environmental isolates and their inhibition by natural zeolite

Acinetobacter baumannii is an emerging human pathogen causing great concern in hospitals. There are numerous studies regarding the virulence factors that contribute to the pathogenesis of A. baumannii clinical isolates, whereas data regarding environmental isolates are missing. The virulence factors (biofilm formation at the air-liquid/solid-liquid interfaces and surface motility) of A. baumannii isolated from natural environment were determined. The influence of natural zeolite (NZ) on the expression of virulence factors was examined by addition of 1 and 10% of NZ into the growth medium. In total 24 environmental isolates of A. baumannii were recovered from different stages of the secondary type of municipal wastewater treatment plant. 14 isolates were multi-drug resistant, while 10 of them were sensitive to all antibiotics tested. Isolates sensitive to antibiotics were statistically significantly more hydrophobic and formed stronger biofilm and pellicles than multi-drug resistant isolates. Biofilm and pellicle formation were statistically significantly positive correlated with hydrophobicity of cells. Biofilm formation and twitching motility were significantly inhibited by the addition of 1% of NZ into the growth medium due to the immobilization of bacterial cells onto NZ particles, while pellicle formation and swarming motility were inhibited only by the addition of 10% of NZ. NZ is a promising material for the reduction of the A. baumannii virulence factors and could find application in control of the adherence and subsequent biofilm formation of this emerging pathogen on abiotic surfaces.