Tjernberg, I. & Ursing. J. Clinical strains of ,lcinewhartrr classified by DNA-DNA hybridization. APMIS A collection of .-lcincrohn~tcr strains consisting of I68 consecutive clinical strains and 30 type and reference strains was studied by DNA-DNA hybridization and a few phenotypic tests. The field strains could be allotted to 13 DNA groups. By means of reference strains ten of these could be identified with groups described by Boiriw & Grirnonr (1986). while three groups were new: they were given the numbers 13-1 5. The type strain of .4. ruclior~~.~i.s,m.~recently described by Ni. rhimuru et al. ( 1988) was shown to be a member of DNA group 12. which comprised 3 1 clinical isolates. Of the 19 strains of A . ,jrinii. eight showed hemolytic activity on sheep and human blood agar and an additional four strains on human blood agar only.Strains of this species have previously been regarded as non-hemolytic. Reciprocal DNA pairing data for the reference strains of the DNA groups were treated by UPGMA clustering. The reference strains for .4. c~~~l~~o u r c~~i c~i r .~..4. haiiriiannii and for DNA groups 3 and 13 formed a cluster with about 70% relatedness within the cluster. Other DNA groups joined at levels below 6OYn.

Thirty-one Acinetobacter baumannii strains, comprising 14 strains from 14 outbreaks in different northwestern European cities and 17 sporadic strains, were compared by investigating various properties of the strains including biotype, antibiogram, cell envelope protein electrophoretic profile, ribotype pattern, and the band pattern generated by a novel genomic fingerprinting method, named AFLP, which is based on the selective amplification of restriction fragments. Results showed that 12 strains from unrelated outbreaks were linked together in two clusters according to their similarities by these typing methods, whereas sporadic strains were more heterogeneous. Outbreak strains appeared to be markedly more resistant to antibiotics than nonoutbreak strains. The uniformity of typing characters in two sets of outbreak strains suggests that strains in each cluster have a common clonal origin.

hydrolysis, and assimilation of 14 carbon sources. Of the strains tested, 181 represented 12 DNA groups in the matrix; at a probability level of .0.95, 78% of them were correctly identified, 2.2% were misidentified, and 19.8% were not identified. Seventeen strains represented two DNA groups not included in the matrix; nine of them were incorrectly assigned to a DNA group by these phenotypic tests. Because of problems of separating strains belonging to DNA groups 1, 2, 3, and 13 by using the phenotypic tests proposed by Bouvet and Grimont (Ann. Inst. Pasteur/Microbiol.), we suggest that these groups should be referred to as the Acinetobacter calcoaceticus-A. baumannii complex.

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Occasionally, genomic groups (DNA groups, genomic species) that have been delimited by DNA-DNA pairing may be phenotypically so similar that they cannot be differentiated for the time being. In these situations it seems best to allow a nomenspecies to contain more than one genomic group and to refer to genomic groups of a nomenspecies as genomovars.

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