Some immunological properties of lipopolysaccharide from Acinetobacter baumannii

Acinetobacter baumannii, mainly biotype 9, is an important nosocomial oppor tunist pathogen in Chile and other countries. The biological basis of its v irulence and prevalence is still unknown. As lipopolysaccharide (LPS) is of ten associated with virulence, some biological properties of purified LPS f rom seven nosocomial isolates, comprising four isolates of A. baumannii bio type 9, two isolates of biotype 8 and one isolate of biotype 1, were invest igated. LPS was extracted and purified from each isolate by the hot phenol- water method, and its ability to elicit a mitogenic response and to induce the synthesis of alpha tumour necrosis factor (TNF-alpha) in mouse spleen c ells was determined, Activity was evaluated lit vivo by determining the spl enic index in comparison with LPS from Salmonella Typhimurium. All seven LP S samples were mitogenic on the basis of cellular proliferation experiments and six induced synthesis of TNF-alpha, Similar results mere obtained in i n-vivo experiments in which LPS induced spleen cell growth, as shown by det ermination of the splenic index, These results suggest that the LPS of A, b aumannii might contribute to the pathogenic properties of this species.