Insertion elements in Staphylococcus intermedius

Staphylococcus intermedius cultures from dogs, pigeons, horses and mink were investigated for the prevalence of the insertion elements IS256 and IS257 in relation to their antibiotic resistance. Copies of IS256 could not be detected in any of the Staph. intermedius isolates tested whereas single copies of IS257 occurred in the isolates from dogs and horses. The mink strains did not harbour IS257 elements, whereas Staph. intermedius isolates from pigeons carried multiple copies of IS257 as predicted from the hybridization patterns obtained with a gene probe derived from the internal part of the IS257-encoded transposase gene. Independently of the origin of the Staph. intermedius isolates, all IS257 copies were found to be located in the chromosomal DNA. The large number of chromosomal IS257 copies in the pigeon strains might help to explain chromosomal multiresistance in many of those strains.