Separation of Salmonella typhimurium DT2 and DT135: Molecular characterization of isolates of avian origin

In Denmark, 0.4 and 3.4% of the human Salmonella Typhimurium cases registered between 1988 and 1993 were caused by DT2 and DT135, respectively. Separation of these two phage types was, however, problematic as only minor differences in lysis pattern and lysis strength occurred. Molecular characterization of 23 Danish isolates, 10 German isolates and the two type strains have subsequently been performed. With only minor exceptions, strains examined could be separated by combination of 0:5 agglutination, ribotyping, and PFGE typing into two major groups in conformity with their phage types. The differences between the two groups were, however, very small and it has not been completely clarified whether this grouping is the result of two independent types or of two related lines developing in different environments. It is concluded that the classification of related phage types DT2 and DT135 has to be supported by molecular methods.