Molecular characterization of endemic salmonella infections ... - Evira

2.5.2.4 IS200-typing
Insertion sequences (IS) are mobile genetic elements that contain only the genes that are
necessary for their own transposition. In 1983, Lam and Roth (1983) described a 708 base pair
Salmonella-specific insertion sequence, IS200. This insertion sequence has been shown to be
distributed on conserved loci on the chromosome of many Salmonella serotypes in copy numbers
ranging between one and 25 (Gibert et al 1990). IS200-typing is based on the number and
distribution of IS200 elements in the genome. It has been found to be more valuable for
differentiation within serotypes where phage typing schemes do not exist, such as for S.
Brandenburg and S. Infantis (Threlfall et al 1994). In combination with ribotyping, it is an especially
suitable method of discrimination for epidemiological purposes (Threlfall et al 1994) unless the
copy number happens to be low and only a few bands are generated (Stanley and Saunders
1996).
The absence of IS200 has been noted in strains of S. Agona, S. Daressalam and S. Hadar (Olsen
2000). However, Fantasia et al (1997) found IS200-typing to be an extremely useful tool for
discriminating clones of S. Hadar in their study on isolates from sporadic and epidemic cases.
Differentiation within the phage type could not be achieved for S. Enteritidis. On the other hand,
discrimination has been achieved both within serotype and phage type for S. Typhimurium
(Threlfall et al 1994). Distinct genotypes for S. Paratyphi B and S. Java were distinguished by
IS200-typing, with 13 unique IS200-profiles, for the majority of strains shared the predominant 16S
rRNA profile (Ezquerra et al 1993). In a study on 32 selected isolates of Salmonella serogroup D1
(O antigen group 9), Stanley et al (1994) observed 20 different IS200-profiles though four isolates
had no copies of the insertion sequence at all. In S. Infantis, for which either phage typing or
plasmid profiling per se had not been applicable, the combination of ribotyping and IS200-typing
generated 15 genotypes. Separately, the two methods gave five and 11 profiles, respectively
(Pelkonen et al 1994). In S. Dublin, only one IS200 pattern was seen in the 35 strains examined
(Olsen and Skov 1994). The pattern obtained was identical to that of a previous study on bovine
and human isolates of S. Dublin from England and Wales. In S. Abortusovis, IS200-typing proved
more reliable than plasmid profiling. It also provided information on the geographic origin of the
strains, since the IS200-profiles were less polymorphic in isolates from the same area (Schiaffino
et al 1996).
IS200-typing was more valuable than ribotyping in differentiating isolates of S. Montevideo (Old et
al 2000). In S. Glostrup isolates, both IS200-typing and ribotyping proved valuable, as seven and
three different profiles were detected, respectively (Old et al 1999). Neither IS200-typing nor
ribotyping proved very valuable for a majority of the analysed isolates.
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