Chromosomal fingerprinting of the type strains of serotypes of O-serogroup D1 with the DNA insertion sequence IS generated patterns which were either serotype-specific (e.g., Typhi), or conserved among groups of related serotypes (e.g., Dublin, Rostock and certain phage types of Enteritidis). The number of IS copies varied considerably, and the IS patterns of type strains of serotypes associated with systemic infections in man were specific and suitable for identifying strains within those serotypes. Polymorphism at 16S rRNA gene loci was examined among type strains and 11 16S rRNA gene profiles were characterised. The most prevalent of these was conserved among type strains of 11 serotypes, and the next most prevalent among type strains of nine serotypes; together, they encompassed 15 unique IS profiles. The distribution and mol. wts of plasmids carrying (virulence) genes could be directly related to certain chromosomal genotypes defined by IS patterns. The presence of virulence plasmids in serotypes Lomalinda, Antarctica and Wangata is reported for the first time. Comparison of 16S rRNA gene profiles and IS patterns provides a definition of genotype that is applicable to epidemiological studies of various group D1 serotypes and should prove particularly useful for those lacking plasmid DNA.


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