Usefulness of phage typing and "two-way ribotyping" to differentiate Salmonella enteritidis strains.

The capacity to differentiate Salmonella enteritidis strains by phage typing and "two-way ribotyping" performed with PstI and SphI was evaluated. The typeability was 96.8% in phage typing and 100% in ribotyping. The series was differentiated into 13 phage types, 19 combined ribotypes, and 39 subtypes or clonal lines by combining results from both methods (of which 11, 13, and 35, respectively, were represented by natural strains). Ribotyping differentiated strains ascribed to PTs 1, 4, 6a, 7, 8, RDNC and UPT. Conversely, some strains of PTs 1, 4, 5a, 6, 6a, 7, 34, RDNC and UPT fall into the most frequent combined ribotype. A dendrogram of genetic similarity generated from the combined ribotypes was traced, and, at a 0.82 similarity level, it showed a major cluster (including 17 combined ribotypes, 88.4% strains ascribed to all PTs tested except PT11), a minor cluster, and four additional lines more loosely related.