[Show abstract][Hide abstract] ABSTRACT: Glycopeptide resistance has been studied in detail in enterococci and staphylococci. In these microorganisms, high-level resistance
is achieved by replacing the C-terminal d-alanyl-d-alanine of the nascent peptidoglycan with d-alanyl-d-lactate or d-alanyl-d-serine, thus reducing the affinities of glycopeptides for cell wall targets. Reorganization of the cell wall is directed
by the expression of the van gene clusters. The identification of van gene homologs in the genomes of several glycopeptide-producing actinomycetes suggests the involvement of a similar self-resistance
mechanism to avoid suicide. This report describes a comprehensive study of self-resistance in Actinoplanes teichomyceticus ATCC 31121, the producer of the clinically relevant glycopeptide teicoplanin. A. teichomyceticus ATCC 31121 showed a MIC of teicoplanin of 25 μg/ml and a MIC of vancomycin of 90 μg/ml during vegetative growth. The vanH, vanA, and vanX genes of A. teichomyceticus were found to be organized in an operon whose transcription was constitutive. Analysis of the UDP-linked peptidoglycan precursors
revealed the presence of UDP-glycomuramyl pentadepsipeptide terminating in d-alanyl-d-lactate. No trace of precursors ending in d-alanyl-d-alanine was detected. Thus, the van gene complex was transcribed and expressed in the genetic background of A. teichomyceticus and conferred resistance to vancomycin and teicoplanin through the modification of cell wall biosynthesis. During teicoplanin
production (maximum productivity, 70 to 80 μg/ml), the MIC of teicoplanin remained in the range of 25 to 35 μg/ml. Teicoplanin-producing
cells were found to be tolerant to high concentrations of exogenously added glycopeptides, which were not bactericidal even
at 5,000 μg/ml.