Clinical findings in 36 immunosuppressed patients with lower respiratory tract infection or bacteremia withActinobacillus hominis are described. Animal contact was only recorded for three patients; nine patients died despite appropriate antimicrobial treatment. Although infections with this microorganism seem to be rare, the fact that 37 of 46 strains characterized in this study have been found in Copenhagen indicates that underreporting may occur. A. hominis is phenotypically relatively homogeneous but can be difficult to differentiate from other Actinobacillus species unless extensive biochemical testing is performed. Mannose-positive strains of A. hominis are especially difficult to differentiate from A. equuli. Attempts to identify A. hominis by automatic identification systems may lead to misidentifications. Ribotyping and DNA-DNA hybridization data show that A. hominis is a homogeneous species clearly separated from other species within the genus Actinobacillus.The genus Actinobacillus is comprised of species that are animal pathogens, the only exceptions being Actinobacillus ureae and Actinobacillus hominis, which appear to be highly adapted to humans. A. ureae was first described as a human respiratory tract pathogen in 1960 (8). In 1981, Friis-Møller reported on 17 cases of respiratory tract infections with an "A. ureae-like" bacterium, which was classified as a distinct species, A. hominis (5). Since then, only a few reports of diseases caused by this microorganism have been reported in the literature; these have, however, involved invasive disease (6, 12).Since we now have a collection of 46 A. hominis strains isolated from various European countries, including blood culture isolates, we report here on clinical findings from patients infected with this microorganism. Furthermore, we investigate strain variability within A. hominis and describe its relationship to closely related species of the family Pasteurellaceae as determined by conventional methods, ribotyping, and DNA-DNA hybridization, and we examine the accuracy of commercial identification systems in this area. MATERIALS AND METHODSStrains. The 46 A. hominis isolates examined in the present study are listed in Table 1. Thirty-eight isolates from 37 patients (one patient had A. hominis isolated twice from the sputum with an interval of 15 months) were found in Copenhagen at five different departments of clinical microbiology from 1977 to 1999. There were two isolates each from Greenland, Germany, and France and one each from the Czech Republic and Sweden. The majority of isolates were found in the respiratory tract (sputa and tracheal and bronchial secretions), one was from the pleural fluid, and four were from blood. Selected strains were studied for DNA-DNA hybridization levels and were characterized by automatic identification systems (vide infra). Twenty type and reference strains from taxa related to A. hominis and used for comparison in the bacteriological study are listed in Table 2. Of these, only the Haemophilus species and A. ureae a...

Cardiobacterium valvarum is a newly recognized human pathogen related to infective endocarditis. Cardiobacterium species are, however, only rarely the aetiology of infective endocarditis. An infective endocarditis case is presented and, additionally, phenotypic and phylogenetic comparison of a further 10 collection strains, representing the two species within the genus, was performed. C. valvarum was isolated from the blood and DNA was present in valvular tissue (partial 16S rRNA gene analysis) from a 64-year-old man with infective endocarditis of the mitral valve, rupture of chordae and prolapse of pulmonary valves in addition to a fluttering excrescence. A mechanical mitral valve and neochordae were inserted successfully. Phenotypically, the two species within the genus Cardiobacterium resemble each other greatly. When using the Vitek 2 Neisseria-Haemophilus identification card, the reaction for phenylphosphonate was positive for all Cardiobacterium hominis strains, but negative for all C. valvarum strains, thereby separating the two species. The two species made up two separate clusters by phylogenetic examination using 16S rRNA gene sequence analysis.

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Taxonomy and identification of fastidious Gram negatives are evolving and challenging. We compared identifications achieved with the Vitek 2 Neisseria-Haemophilus (NH) card and partial 16S rRNA gene sequence (526 bp stretch) analysis with identifications obtained with extensive phenotypic characterization using 100 fastidious Gram negative bacteria. Seventy-five strains represented 21 of the 26 taxa included in the Vitek 2 NH database and 25 strains represented related species not included in the database. Of the 100 strains, 31 were the type strains of the species. Vitek 2 NH identification results: 48 of 75 database strains were correctly identified, 11 strains gave `low discrimination´, seven strains were unidentified, and nine strains were misidentified. Identification of 25 non-database strains resulted in 14 strains incorrectly identified as belonging to species in the database. Partial 16S rRNA gene sequence analysis results: For 76 strains phenotypic and sequencing identifications were identical, for 23 strains the sequencing identifications were either probable or possible, and for one strain only the genus was confirmed. Thus, the Vitek 2 NH system identifies most of the commonly occurring species included in the database. Some strains of rarely occurring species and strains of non-database species closely related to database species cause problems. Partial 16S rRNA gene sequence analysis performs well, but does not always suffice, additional phenotypical characterization being useful for final identification.