VanD-Type Vancomycin-Resistant Enterococcus faecium and Enterococcus faecalis

Abstract

Enterococcus faecium clinical isolates A902 and BM4538, which were resistant to relatively high levels of vancomycin (128 and 64 g/ml, respectively) and to low levels of teicoplanin (4 g/ml), and Enterococcus faecalis clinical isolates BM4539 and BM4540, which were resistant to moderate levels of vancomycin (16 g/ml) and susceptible to teicoplanin (0.25 g/ml), were studied. Prior to the late 1980s, Enterococcus faecium and Enterococcus faecalis were considered uniformly susceptible to vancomycin, which was often the only antibiotic effective against multiresistant strains. Therefore, reports of vancomycin resistance in enterococci from Europe in 1988 (32, 48) and subsequently from the United States raised considerable concern (19). Since then, vancomycin-resistant enterococci have become increasingly prevalent.Glycopeptide resistance in enterococci results from the production of modified peptidoglycan precursors ending in D-Ala-D-Lac (VanA, VanB, and VanD) or D-Ala-D-Ser (VanC, VanE, and VanG), to which glycopeptides exhibit low binding affinities, and from the elimination of the high-affinity D-Ala-D-Ala-ending precursors synthesized by the host Ddl ligase (10,20,22,44). Acquired resistance to glycopeptides in the three D-Ala-D-Lac types, VanA, VanB, and VanD, can be classified depending on the levels of resistance to vancomycin and susceptibility or resistance to teicoplanin (10,22). VanA-type strains display high-level inducible resistance to both vancomycin and teicoplanin, whereas VanB-type strains have various levels of inducible resistance to vancomycin only, since teicoplanin is not an inducer (10). VanD-type strains are characterized by constitutive resistance to moderate levels of both glycopeptides (22)

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…The basic organization of the vanD operons, which are located exclusively on the chromosome, is similar to that of the vanA and vanB clusters (Casadewall and Courvalin 1999;Boyd et al, 2000;Depardieu et al, 2003b;Depardieu et al, 2004;Boyd et al, 2004). Genes equivalent to vanZ or vanW are absent.…”

“…1) which cannot be explained on the basis of already known DNA sequence diversities. Due to different strategies in establishing those complex and highly regulated networks independently and via different routes five different vanD cluster types had arranged and were characterized so far (Boyd et al, 2000;Depardieu et al, 2004). Up to now, VanD-type resistance still is a rare van resistance type among enterococci but has been described in a VanC type E. gallinarum N04-0414, too (Boyd et al, 2006b).…”

Detection of glycopeptide resistance genes in enterococci by multiplex PCR

“…5 VanD type strains are resistant to moderate level of vancomycin and low level of teicoplanin. 6 There are three VanC genes namely Van C1, Van C2 and Van C3. These genes are specific to the motile VRE species Enterococcus gallinarum, Enterococcus casseliflavus and Enterococcus flavescens respectively.…”

First Infection with VanD-Type Glycopeptide-Resistant Enterococcus faecium in Europe

“…Since 1988, many reports described the increase of vancomycin resistance in enterococci from Europe and the United States (6,13). This resistance to glycopeptides occurs via a common mechanism involving modification of the peptidoglycan biosynthetic pathway (8). Five phenotypes of acquired glycopeptide resistance have been identified in enterococci.…”

“…VanA and VanB are the most common types. They are caused by complex gene clusters that may be plasmid and/or transposon carried (8). VanE and VanG types have each been identified in single strains of Enterococcus faecalis (11,15).…”