IDENTIFICATION OF ACINETOBACTER ISOLATES IN THE A-CALCOACETICUS A-BAUMANNII COMPLEX BY RESTRICTION ANALYSIS OF THE 16S-23S RIBOSOMAL-RNA INTERGENIC SPACER SEQUENCES

Members of the genus Acinetobacter are reported to be involved in hosp ital-acquired infections with an increasing frequency. However, clinic al laboratories still lack simple methods that allow complete identifi cation of some pathogenic species, i.e., those corresponding to A. bau mannii (DNA group or genospecies 2), unnamed genospecies 3 and 13, and two new genospecies that have recently been described. In fact, a com plete discrimination between these species is possible only by DNA-DNA hybridization or ribotyping. Both of these techniques are complex and time-consuming and cannot be performed in most clinical laboratories. As a consequence, isolates belonging to these genospecies are often n ot differentiated and included, together with the environmental genosp ecies 1, in the A. calcoaceticus-A. baumannii complex. In this report, a simple and rapid method for the identification of the genospecies b elonging to the A. calcoaceticus-A. baumannii complex is proposed. It is based on the combined digestion by the restriction endonucleases Al uI and NdeII of the DNA fragments resulting from the amplification of the 16S-23S rRNA intergenic spacer sequences. The analysis of 36 strai ns characterized by DNA-DNA hybridization in previous studies showed t hat the restriction profiles obtained are highly reproducible and char acteristic for each genospecies. Moreover, extending this study to 68 clinical strains, which were assigned to the A. calcoaceticus-A. bauma nnii complex by phenotypic tests, confirmed the existence of a panel o f limited and well-conserved restriction patterns and allowed the iden tification of the strains tested. This study thus proposes the detecti on of restriction length polymorphism in the spacer sequences between the 16S and 23S rRNA genes as a method for the identification of isola tes in the A. calcoaceticus-A. baumannii complex.