Molecular characterization of the genera Proteus, Morganella, and Providencia by ribotyping

Abstract

The so-called Proteus-Providencia group is constituted at present by three genera and 10 species. Several of the recognized species are common opportunistic pathogens for humans and animals. Different methods based on the study of phenotypic characters have been used in the past with variable levels of efficiency for typing some species for epidemiological purposes. We have determined the rRNA gene restriction patterns (ribotypes) for the type strains of the 10 different species of the genera Proteus, Morganella, and Providencia. Visual inspection of EcoRV- and HincII-digested DNA from the type strains showed remarkably different patterns for both enzymes, but EcoRV provided better differentiation. Both endonucleases were retained to study a large number of wild and collection strains belonging to the different species. Clinical isolates of Proteus mirabilis, Proteus penneri, Morganella morganii, and Providencia heimbachae showed patterns identical or very similar to those of the respective type strains, so that groups of related patterns (ribogroups) were found to correspond to the diverse species. On the contrary, distinct ribogroups were detected within Providencia alcalifaciens (two ribogroups with both enzymes), Providencia rettgeri (four ribogroups with EcoRV and five with HincII), Providencia stuartii (two ribogroups with EcoRV), Providencia rustigianii (two ribogroups with HincII), and Proteus vulgaris (two ribogroups with both enzymes). The pattern shown by the ancient P. vulgaris type strain NCTC 4175 differed considerably from both P. vulgaris ribogroups as well as from the newly proposed type strain ATCC 29905 and from any other strain in this study, thus confirming its atypical nature. Minor differences were frequently observed among patterns of strains belonging to the same ribogroup. These differences were assumed to define ribotypes within each ribogroup. No correlation was observed between ribogroups or ribotypes and biogroups of P. vulgaris, P. alcalifaciens, P. stuartii, and P. rettgeri. Since, not only different species showed different rRNA gene restriction patterns, but also different ribogroups and ribotypes have been found in the majority of the species, ribotyping would be a sensitive method for molecular characterization of clinical isolates belonging to the genera Proteus, Morganella, and Providencia.

FIG. 1

EcoRV restriction patterns of type strains. Lanes: M, molecular weight standard; 1, P. mirabilis NCTC 11938; 2, P. vulgaris NCTC 4175; 3, P. vulgaris ATCC 29905; 4, P. penneri NCTC 12737; 5, P. myxofaciens NCIMB 13273; 6, M. morganii NCTC 235; 7, P. alcalifaciens NCTC 10286; 8, P. stuartii NCTC 11800; 9, P. rettgeri NCTC 11801; 10, P. rustigianii NCTC 11802; 11, P. heimbachae NCTC 12003.

FIG. 2

Dendrogram obtained by comparison of EcoRV ribotyping patterns of the type strains of the 10 species studied. The distance matrix was generated by using the complement of Dice similarity coefficients and the average-linkage algorithm with a 4% tolerated error.

FIG. 3

HincII restriction patterns of type strains. Lanes: M, molecular weight standard; 1, P. mirabilis NCTC 11938; 2, P. vulgaris NCTC 4175; 3, P. vulgaris ATCC 29905; 4, P. penneri NCTC 12737; 5, P. myxofaciens NCIMB 13273; 6, M. morganii NCTC 235; 7, P. alcalifaciens NCTC 10286; 8, P. stuartii NCTC 11800; 9, P. rettgeri NCTC 11801; 10, P. rustigianii NCTC 11802; 11, P. heimbachae NCTC 12003.

FIG. 4

Dendrogram obtained by comparison of HincII ribotyping patterns of the type strains of the 10 species studied. The distance matrix was generated by using the complement of Dice similarity coefficients and the average-linkage algorithm with a 4% tolerated error.

FIG. 5

Dendrogram based on the EcoRV ribotyping patterns of the strains listed in Table 1. The distance matrix was generated by using the complement of Dice similarity coefficients and the average-linkage algorithm with a 4% tolerated error.

FIG. 6

Dendrogram based on the HincII restriction patterns of 66 strains listed in Table 1. The distance matrix was generated by using the complement of Dice similarity coefficients and the average-linkage algorithm with a 4% tolerated error.