Antimicrobial Susceptibility Testing of a Clinical Isolate of Vancomycin-Dependent Enterococcus Using D-Alanine-D-Alanine as a Growth Supplement

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…Consequently depletion of D-Ala-D-Ala dipeptides leads to an impaired cell wall synthesis. The effect could be complemented by providing the missing D-Ala-D-Ala dipeptide (Sng et al, 1998a) or similar di-or depsipeptides. Vancomycin is capable of inducing the VanA or VanB type resistance and thus providing DAla-D-Lac as the necessary substrate for a revived cell wall synthesis.…”

“…Mutations in the histidine kinase or the regulator may bypass the inducing property of the antimicrobial compound in leading to a constitutive resistance phenotype not requiring vancomycin anymore. This switch from inducible to constitutive vancomycin resistance phenotype may also appear independently from a previous vancomycin dependence phenotype (Sng et al, 1998b;Baptista et al, 1999). As described recently in a VanB type VRE, a mutation in the transcription terminator of the regulatory genes resulting in transcriptional readthrough of the resistance genes from the P RB promoter in the absence of vancomycin may also circumvent vancomycin dependence and lead to a constitutive phenotype (San Millan et al, 2009b).…”

Enterococci: Susceptibility, Resistance, and Now Dependence on Vancomycin

“…2 0 Subsequent studies now report detection of VDE in patients with known VRE (Table) by using either vancomycin or DADA disks. 4 ' 20 " 24 Growth of VDE in the presence of DADA suggests that the isolate has stopped expressing the normal DADA ligase and becomes dependent on either vanA or vanB ligase for cell-wall synthesis. Growth of VDE, in the presence of vancomycin, may involve vancomycin-induced production of D-alanine-Dlactate.…”

“…Sng et al 4 provide the sixth case report of VDE, along with a method for laboratory detection independent of vancomycin supplementation. The clinical scenario is that of a renal transplant recipient who initially had infections requiring prolonged treatment with vancomycin.…”

“…Although DADA supplementation has been previously described for VDE, Sng et al 4 have identified the optimal DADA supplementation for this isolate. In addition, the molecular diagnostic techniques confirmed the genetic relatedness among the the patient's initial blood isolate of VRE, subsequent VDE, revertant mutant, and autopsy isolate.…”