ABSTRACT
A range of European habitats was screened by PCR for detection of the oxytetracycline resistance genes otr(A) and otr(B), found in the oxytetracycline-producing strain Streptomyces rimosus. Primers were developed to detect these otr genes in tetracycline-resistant (Tc(R)) streptomycete isolates from environmental samples. Samples were obtained from bulk and rhizosphere soil, manure, activated sludge and seawater. The majority of Tc(R) streptomycetes originated from bulk and rhizosphere soil. Fewer Tc(R) streptomycetes were isolated from manure and seawater and none from sewage. By PCR, three out of 217 isolates were shown to contain the otr(A) gene and 13 out of 217 the otr(B) gene. Surprisingly, these genes were detected in taxonomic groups not known as tetracycline-producing strains. The majority of the otr gene-carrying strains was assigned to S. exfoliatus or S. rochei and originated from all habitats from which Tc(R) streptomycetes were obtained. Our results indicated that the occurrence of otr(A) and otr(B) genes in natural environments was limited and that otr(B), in comparison to otr(A), seemed to be more common.
Subject(s)
Bacterial Proteins/genetics , Oxytetracycline/pharmacology , Soil Microbiology , Streptomyces/genetics , Tetracycline Resistance/genetics , Bacterial Proteins/analysis , DNA Primers/genetics , Genes, Bacterial/genetics , Polymerase Chain Reaction/methods , Streptomyces/drug effects , Streptomyces/isolation & purificationABSTRACT
A SRS search in the GenBank/EMBL databases for entire genes encoding efflux-mediated resistance allocated to a recognized tetracycline determinant revealed the existence of at least 87 genes. DNA-based and protein sequence analyses of representatives from the different efflux-mediated tetracycline determinant groups were performed and allowed us to propose a revision of the current grouping on the basis of our new evolutionary trees. On the other hand, similarity, topology, and hydropathy analyses of some representatives from 12-transmembrane segments (TMS) and 14-TMS proteins lead us to perform meaningful sequence alignments of recognized or putative 12-TMS and 14-TMS proteins truncated to their first 200 amino acids (alpha-domain of the protein). For all aligned truncated proteins, including old and recently discovered tetracycline resistance determinants, significant similarities along this segment were demonstrated and three new conserved motifs identified, reinforcing the hypothesis of a common ancestry for the alpha-domain of all tetracycline-efflux pumps.
