Inducible and constitutive expression of vanC-1-encoded resistance to vancomycin in Enterococcus gallinarum

Abstract

Clinical isolates Enterococcus gallinarum AIB39 and E. gallinarum GS1 were studied to establish whether the expression of vanC-1-mediated resistance may be inducible or constitutive. By growth curve analysis, strain AIB39 exhibited the same lag period (i.e., 1 to 1.5 h) whether it was subcultured to unsupplemented brain heart infusion broth or broth containing 6 g of vancomycin per ml, a growth pattern typical of constitutively expressed resistance. Use of high-performance liquid chromatography ( Acquired vancomycin resistance among enterococci, most usually associated with Enterococcus faecium and Enterococcus faecalis, is mediated by vanA and vanB genes that encode ligases capable of producing altered UDP-MurNAc-pentapeptide precursors for which vancomycin has diminished affinity (1). The vancomycin resistance exhibited by Enterococcus gallinarum is generally considered a constitutively expressed intrinsic characteristic of this species (1,18,27,28). The intrinsic nature of this resistance is supported by the finding that the vanC-1 gene, which encodes a ligase that catalyzes the formation of D-Ala-D-Ser, has consistently been found in every E. gallinarum strain examined and has not been found in other enterococcal species (9,18,22). However, recent findings suggest that although resistance may be intrinsic, expression may not always be constitutive (3,22).For other gram-positive organisms considered to be intrinsically and constitutively resistant, such as Leuconostoc, Lactobacillus, and Pediococcus species, evidence suggests the presence of a single ligase system (3, 15). The only peptidoglycan precursor found in these organisms is UDP-In contrast, recent reports have established the likely existence of at least two ligases in E. gallinarum. This organism has exhibited the capacity to produce UDP-MurNAc-L-Ala-DGlu-L-Lys-D-Ala-D-Ala (UDP-MurNac-tetrapeptide-D-Ala) cell wall precursor and the altered precursor MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ser (UDP-MurNac-tetrapeptide-D-Ser), which is catalyzed by the vanC-1-encoded ligase (3, 22). The ability to produce the wild-type cell wall precursor UDPMurNac-tetrapeptide-D-Ala and one with a decreased affinity for vancomycin (i.e., UDP-MurNac-tetrapeptide-D-Ser) is a feature that is strikingly similar to the inducible, acquired glycopeptide resistance encoded by vanA and vanB. In these systems induction results in the production of UDP-MurNactetrapeptide-D-Lac that has significantly reduced vancomycin affinity compared with that of the UDP-MurNac-tetrapeptide-D-Ala peptidoglycan precursor (1, 4, 10).The presence of two ligases in E. gallinarum, a species heretofore considered to express resistance constitutively, is somewhat perplexing. In this report we establish the ability of E. gallinarum to inducibly or constitutively express vanC-1-mediated vancomycin resistance. Although vanC-1 may be intrinsic to this species, these findings raise several questions regarding the intrinsic nature of the regulatory mechanisms that accompany vanC-1. MATERIALS AND METHODSSource, i...

Validation of VITEK 2 Version 4.01 Software for Detection, Identification, and Classification of Glycopeptide-Resistant Enterococci

“…The GRE isolates were identified to the species level on the basis of standard methods, like colony morphology, Gram stain, catalase and pyrase testing, the presence of the Lancefield group D antigen, pigment production, motility testing, methyl-alpha-D-glucopyranoside (MPG) acidification tests, and the API STREP system (bioMérieux, Nürtingen, Germany). Strains carrying the vanC1 or the vanC2 gene were identified as Enterococcus gallinarum or Enterococcus casseliflavus (4,14). The standard iden-tification results were compared with those obtained with the new VITEK 2 cards (GP identity card) for the identification gram-positive cocci, according to the manufacturer's instructions.…”

Enterococcus gallinarum Endocarditis Occurring on Native Heart Valves

“…gallinarum has the capacity to express resistance to lowlevel vancomycin, with vancomycin MICs ranging from 2 to 32 g/ml, and the strains can be classified as intermediate or susceptible to this antibiotic (2,3,25,31). This feature is conferred by the chromosomal vanC1 gene (14,15,24,29,32). Antibiotic susceptibility patterns indicate that most isolates are ampicillin susceptible (6).…”

A vancomycin-inducible lacZ reporter system in Bacillus subtilis: induction by antibiotics that inhibit cell wall synthesis and by lysozyme

“…(9,11,13,24,28) has emerged in recent years as a major health problem in the treatment of infectious diseases (22,29,31). The inducible form of resistance can also serve as a transitional step to constitutive resistance, with important consequences for the clinical effectiveness of antibiotics that belong to this group (12,15,25,26).…”