Deoxyribonucleic acid sequence common to staphylococcal and streptococcal plasmids which specify erythromycin resistance

Terminal nucleotide sequences of Tn551, a transposon specifying erythromycin resistance in Staphylococcus aureus: homology with Tn3

The erythromycin resistance determinant of Staphylococcus aureus plasmid pI258 resides on a 5.3 kb transposon, Tn551. We have determined DNA sequences surrounding the junctions between the transposon and the flanking DNA in the wild-type plasmid, in an insertion into a second plasmid, and in two transposon-related deletions. The ends of the transposon consist of an inverted repeat of 40 base pairs flanked by a direct repeat of 5, thus placing the transposon in the same class as Tn3, IS2, Tn501, gamma delta, and bacteriophage Mu. Interestingly, we find that the terminal sequences of the 40 base pairs inverted repeat are very similar to the ends of Tn3, a transposon which one would not have expected to show any relation to Tn551. This result suggests common ancestry for Tn3 and Tn551. The inverted repeat sequence of Tn551 also contains (with one additional inserted base) the internal heptanucleotide sequence which has been found to be common to most of the transposable elements that generate 5-base pair direct repeat sequences.

Plasmid-mediated resistance to aminocyclitol antibiotics in group D streptococci

Streptococcus faecalis BM4100 was resistant to high levels of gentamicin, kanamycin, and structurally related antibiotics. The genes conferring resistance to aminocyclitols in this strain were carried by a plasmid, pIP800, self-transferable to other S. faecalis strains. The aminocyclitol resistance was mediated by constitutively synthesized phosphotransferase and acetyltransferase activities. It was inferred that phosphorylation occurred at the 2"-hydroxyl group and that acetylation occurred at the 6'-hydroxyl group of the aminocyclitols. The enzyme activities were not separable by gel filtration or by isoelectric focusing. Their apparent molecular weight was 31,000, and their isoelectric point was 5.3. With respect to substrate profile, size, and charge, the transferases from strain BM4100 resembled closely those with identical site specificity described in staphylococci. These results suggest that plasmid gene transfer may occur between the two pathogenic bacterial genera.

Transferability of macrolide, lincomycin, and streptogramin resistances between group A, B, and D streptococci, Streptococcus pneumoniae, and Staphylococcus aureus

The transferability of plasmid pRI405 between various streptococci of groups A, B, and D, Streptococcus pneumoniae, and Staphylococcus aureus is described. pRI405 originated from Streptococcus faecalis and encodes for resistance to macrolides, lincomycin, and streptogramin B (MLS resistance). The host range of the well-documented streptococcal plasmid pAM beta 1 was found to be similar to that of pRI405. Cleavage with restriction enzymes suggests that pRI405 belongs to a related family of MLS resistance plasmids.

Organization and transfer of heterologous chloramphenicol and tetracycline resistance genes in pneumococcus

The cat and tet genes of chloramphenicol- and tetracycline-resistant clinical isolates of Streptococcus pneumoniae from Paris and Japan were shown to be contained in adjacent heterologous insertions into the chromosome. The two insertions transformed laboratory strains at frequencies that were low, unequal, and, for tet, very sensitive to the length of the donor deoxyribonucleic acid strand. In contrast, the transforming activity of cat was relatively stable. There was an unusual asymmetric cotransfer, in that a majority of the tet transformants also acquired cat, whereas only a few of the cat transformants also acquired tet. The evidence for chromosomal insertion came from genetic data showing linkage of cat to a chromosomal gene and from cosedimentation of cat with chromosomal markers in both velocity and dye-buoyancy experiments. Genes on a known plasmid introduced into pneumococcus from Streptococcus faecalis showed very different physical behavior. Most of the transformation properties of these genes can be readily accounted for by analogy to transformation of deletions of normal genes. Whether transposition contributes any of the transfers remains to be determined. The presence of one of the genes in the recipient promoted the integration of the other, demonstrating enhanced accumulation of heterologous genes by a process that did not involve plasmids in the species of concern.