VANA GENE-CLUSTER IN A VANCOMYCIN-RESISTANT CLINICAL ISOLATE OF BACILLUS-CIRCULANS

We report on the cloning and sequencing of the vanA gene cluster prese nt in the glycopeptide-resistant clinical isolate Bacillus circulans V R0709 (R, Fontana, M, Ligozzi, C, Pedrotti, E. M, Padovani, and G, Cor naglia, fur. J, Clin, Microbiol, Infect. Dis, 16:473-474, 1997). The p resence of a vanA-related gene in VR0709 was demonstrated in a PCR ass ay which permitted the specific amplification of an internal segment o f vanA, Southern blotting suggested that the vanA gene was located in the chromosome in a 7,6-kb EcoRI fragment. DNA sequence analysis revea led the presence of all seven genes of the vanA cluster (vanR, vanS, v anH, vanA, vanX, vanY, and vanZ), The degree of identity between homol ogous proteins encoded by Tn1546 and the chromosome of B. circulans VR 0709 ranged from 87 to 95%. Neither PCR nor Southern blotting with spe cific primers and probes, respectively, showed the presence of open re ading frames (ORFs) 1 and 2 which encode the transposase and the resol vase of Tn1546, respectively, the transposon found to carry the vnnA g ene cluster in enterococci, Determination of the sequences of the flan king regions of the van gene cluster of B. circulans revealed perfect inverted repeats of 10 bp which delineated a 9,2-kb region containing the van gene duster and an ORF which encoded a putative protein (178 r esidues) which displayed a low level of identity (28%) to the resolvas e of Tn1546, These results suggest that glycopeptide resistance in B. circulans VR0709 is associated with the acquisition of a vanA gene clu ster which shows a high degree of homology with that of enterococci, I n B. circulans, however, the cluster is not carried by Tn1546 and is b orne by the chromosome.