Organization of the antiseptic resistance gene qacA and Tn552-related beta-lactamase genes in multidrug- resistant Staphylococcus haemolyticus strains of animal and human origins

Abstract

A part (12 kb) of a plasmid containing the beta-lactamase genes of Tn552, the disinfectant resistance gene qacA, and flanking DNA has been cloned from a Staphylococcus haemolyticus isolate and sequenced. This region was used to map the corresponding regions in six other multiresistant S. haemolyticus isolates of human and animal origin. The organizations of the genetic structures were almost identical in all isolates studied. The beta-lactamase and qacA genes from S. haemolyticus have >99.9% identities at the nucleotide level with the same genes from S. aureus, demonstrating that various staphylococcal species able to colonize animal and human hosts can exchange the genetic elements involved in resistance to antibiotics and disinfectants. The use of antibiotics and disinfectants in veterinary practice and animal husbandry may also contribute to the selection and maintenance of resistance factors among the staphylococcal species. Different parts of the 12-kb section analyzed had high degrees of nucleotide identity with regions from several other different Staphylococcus aureus plasmids. This suggests the contribution of interplasmid recombination in the evolutionary makeup of this 12-kb section involving plasmids that can intermingle between various staphylococcal species. The lateral spread of resistance genes between various staphylococcal species is probably facilitated by the generation of large multiresistance plasmids and the subsequent interspecies exchange of them.

FIG. 1.

Physical map of the 12-kb region analyzed in this study containing the β-lactamase genes (the Tn552 bla gene module), antiseptic resistance gene qacA, and a vga-like plasmid inserted downstream of orf2. (A) Organization of bla genes, qacA, and surrounding genes in four strains isolated from the environment of a small-animal veterinary clinic and in two clinical isolates from animals. (B) Organization of bla genes, qacA, and surrounding genes in a clinical isolate of human origin. The bold lines on the restriction map at the top represent the borders of the two cloned HincII fragments of pNVH97A. Shaded genes represent the areas sequenced. pNVH97A (bold) is the only plasmid from which the 12-kb region was completely sequenced. The region was sequenced in four parts: the two HincII clones, the 3-kb bla-qac amplicon, and the 4-kb qac-IS amplicon. The organization of the genes in the remaining animal strains and the human strain was based on hybridization experiments (Table 2) and amplification and sequencing of the bla-qac amplicons of 3 and 5 kb, respectively.

FIG. 2.

Comparison of the approximately 12-kb sequence of pNVH97A to other known plasmid sequences (represented by thin lines). Grey boxes represent regions with high levels of sequence identity (from about 90% for the boxes in light grey to more than 98% for the boxes in darker grey), arrows in IS256 and IS257 denote the directions of the respective transposases, while wider arrows denote the different genes and the directions of those genes. Sources: pIP680, EMBL accession no. AF117259; pS1, EMBL accession no. X52734; pVRSA, EMBL accession no. AP003367; pSK1, EMBL accession nos. X56628 and L23109.