One hundred phenotypic characteristics were determined for 138 clinical and environmental Aeromonas strains. Cluster analysis revealed three major phenons equivalent to the A. hydrophila, A. caviae, and A. sobria groups, each of which contained more than one genospecies and more than one named species. An excellent correlation was found between phenotypic identification and classification based on DNA relatedness. DNA hybridization groups within each of the phenotypic groups were also separable by using a few biochemical characteristics. Key tests were production of acid from or growth on D-sorbitol (which separated DNA hybridization group 3 from groups 1 and 2 within the A. hydrophila phenogroup), growth on citrate (which essentially separated DNA hybridization group 4 from groups 5A and 5B within the A. caviae phenogroup), and growth on DL-lactate (which separated DNA hybridization group 1 from groups 2 and 3 within the A. hydrophila phenogroup as well as group 5A from groups 4 and 5B within the A. caviae phenogroup). All except one strain in the A. sobria phenogroup belonged to DNA hybridization group 8. DNA hybridization groups were not equally distributed among clinical and environmental isolates, suggesting that strains of certain DNA hybridization groups might be less virulent than others.

We examined the taxonomic position of seven Aeromonus isolates, recovered from Flemish and Scottish drinking water production plants and reservoirs, which were previously recognized by numerical analysis of genomic AFLP fingerprints as members of an unknown Aeromonus taxon that most closely resembled the species Aeromonus bestiurum (DNA hybridization group [HG] 2). The new phenotypic and DNA-DNA hybridization data obtained in this study show that the A. bestiurum-like strains constitute a separate Aeramonus species, for which the name Aeromonuspopofii sp. nov. is being proposed. The new species exhibited an internal DNA relatedness ranging from 79 to 100% and was 22 to 63% related to the type or reference strains of other Aeromonus spp. The highest DNA binding values were determined with A. bestiururn (51 to 63%), followed by Aeromonas hydrophila sensu strict0 (HG1; 50 to 60%) and Aeromonus sulmonicidu (HG3; 39 to 55%). Although fingerprints generated by ribotyping and cellular fatty acid analysis often were highly similar, minor differences between the respective fingerprints were of significance for the differentiation of A. popofii from its closest taxonomic neighbors, HG1, HG2, and HG3. Phenotypically, all seven strains ofA. popofii were positive for acid and gas production from D-glucose and glycerol, growth in KCN broth, arginine dihydrolase, DNase, VogesProskauer reaction, and resistance to vibriostatic agent 0/129 and ampicillin but displayed negative reactions for production of urease, tryptophan deaminase, ornithine decarboxylase, and lysine decarboxylase (LDC). None of the strains displayed strong hemolytic activity. The lack of D-sucrose fermentation and LDC production and the ability to utilize DL-lactate as the sole energy and carbon source were useful characteristics for the biochemical separation of A. popofii from A. bestiumm. Other Aeromonus spp. could be differentiated phenotypically from the new species by at least two features. The chromosomal G+C content ofA. popofii ranges from 57.7 to 59.6 mol%. Strain LMG 17541 is proposed as the type strain.

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Development of resistance to nalidixic acid, norfloxacin and ciprofloxacin was observed in five patients with Campylobacter jejuni or Campylobacter coli infection. From all these patients nalidixic acid- and quinolone-susceptible strains were isolated initially, whereas after therapy with norfloxacin or ciprofloxacin strains resistant to these antibiotics were found. Campylobacter strains from the same patient always belonged to the same species and, with the exception of one case, showed identical rRNA gene restriction (rDNA) patterns. This indicates that double-infection with a susceptible and a resistant strain was not responsible for the phenomenon but rather that the infecting strain rapidly developed resistance following treatment.

Beginning in 1990, gram-positive rods resembling Actinomyces pyogenes were found with increasing frequency in mixed cultures from various infectious processes, most of them from patients with otitis, empyema, pilonidal cysts, perianal abscesses, and decubitus ulcers. Ribotyping and hybridization showed that these gram-positive rods could be divided into five groups not related to known Actinomyces species. Biochemical markers for reliable differentiation into these groups, however, could not be found. Therefore, naming new species is not warranted unless parameters are discovered that allow identification without DNA hybridization. These gram-positive rods have been isolated only in mixed cultures with anaerobes, Staphylococcus aureus, Streptococcus "mileri," enterococci, and gram-negative rods. Their exact role in these possibly synergistic infections needs further investigation.