Multiple copies of IS 256 in staphylococci

Abstract

EcoRI-digested cellular DNAs of 150 staphylococcal clinical isolates were probed with a plasmid containing a DNA piece from within the open reading frame of IS 256. Most of the Gm r staphylococcal isolates tested contained more copies of IS 256 than those associated with Tn 4001 carried by these isolates. Three distinct copies of IS 256 together with their flanking DNA were isolated by cloning from an EcoRI digest of the cellular DNA of the Gm r isolate, BM3121. These three copies of IS 256 were shown to be intact. The results from DNA sequencing revealed that one of the three copies is flanked by 8-bp direct repeats, and it is suggested that this may be the result of insertion of the IS 256 at this site by autonomous movement of the IS element. The insert DNA of all three clones hybridized to the cellular DNA prepared from a Staphylococcus aureus strain that carries neither IS 256 nor the aacA-aphD gene. Two of the clones hybridized to several EcoRI fragments of the cellular DNA of this strain, indicating that in these cases IS 256 is flanked by DNA present as several copies on the chromosome.