Trehalose-deficient Acinetobacter baumannii exhibits reduced virulence by losing capsular polysaccharide and altering membrane integrity.

Acinetobacter baumannii has become a leading cause of bacterial nosocomial infections, in part, due to its ability to resist desiccation, disinfection and antibiotics. Several factors contribute to the tenacity and virulence of this pathogen, including production of a broad range of surface glycoconjugates, secretory systems and efflux pumps. We became interested in examining the importance of trehalose in A. baumannii after comparing intact bacterial cells by high-resolution magic angle spinning nuclear magnetic resonance and by noting high levels of this disaccharide, obscuring all other resonances in the spectrum. Since this was observed under normal growth conditions, we speculated that trehalose must serve additional functions beyond osmolyte homeostasis. Using the virulent isolate A. baumannii AB5075 and mutants in the trehalose synthesis pathway, osmoregulatory trehalose synthesis proteins A and B (△otsA and △otsB), we found that the trehalose-deficient △otsA showed increased sensitivity to desiccation, colistin, serum complement and peripheral blood mononuclear cells, while trehalose-6-phosphate producing △otsB behaved similar to the wild-type. The △otsA mutant also demonstrated increased membrane permeability and loss of capsular polysaccharide. These findings demonstrate that trehalose deficiency leads to loss of virulence in A. baumannii AB5075.