Genomic groups and biochemical profiles of clinical isolates of Enterobacter cloacae

A collection of 123 clinical strains presumptively identified as Enterobacter cloacae and 12 type and reference strains of Enterobacter spp. were genotypically investigated by a quantitative bacterial dot method for DNA-DNA hybridization, giving an estimate of delta Tm (difference in thermal denaturation midpoint between homologous and heterologous duplexes). The API 20E system was used for phenotypic characterization. Using discontinuities in the values of delta Tm as criterion, five genomic groups of E. cloacae could be demonstrated, eleven ungrouped strains representing at least one additional group. Nine API profiles were found, the ideal phenotype of E. cloacae (i.e. the phenotype showing the most common reaction for the species in all tests studied) being the most frequently found. The type strain of E. cloacae and the reference strain CDC 1347-71 represented rather small genomic groups of three and eight strains respectively, most of them inositol positive. A majority of 98 isolates formed one single genomic group, biochemically dominated by the ideal phenotype. The genomic groups could not be differentiated phenotypically. At present there seems to be no reason for an attempt to split E. cloacae into two or more species. The type strain of E. dissolvens showed itself to be closely related to the type strain of E. cloacae (delta Tm 2.3 degrees C), indicating that the two species may be regarded as subjective synonyms.