Open AccessNew Combinations of Mutations in VanD-Type Vancomycin-Resistant Enterococcus faecium , Enterococcus faecalis , and Enterococcus avium Strains
Author(s) -
Florence Depardieu,
Marie-Laure Foucault,
Jan M. Bell,
Anne Dubouix,
M. Guibert,
JeanPhilippe Lavigne,
Marion Levast,
Patrice Courvalin
Publication year - 2009
Publication title -
antimicrobial agents and chemotherapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.07
H-Index - 259
eISSN - 1070-6283
pISSN - 0066-4804
DOI - 10.1128/aac.01348-08
Subject(s) - teicoplanin , enterococcus faecalis , enterococcus faecium , microbiology and biotechnology , enterococcus , biology , vancomycin , enterococcus hirae , escherichia coli , gene , bacteria , biochemistry , genetics , antibiotics , staphylococcus aureus
We studied the clinical isolatesEnterococcus faecium NEF1, resistant to high levels of vancomycin (MIC, 512 μg/ml) and teicoplanin (MIC, 64 μg/ml);Enterococcus faecium BM4653 and BM4656 andEnterococcus avium BM4655, resistant to moderate levels of vancomycin (MIC, 32 μg/ml) and to low levels of teicoplanin (MIC, 4 μg/ml); andEnterococcus faecalis BM4654, moderately resistant to vancomycin (MIC, 16 μg/ml) but susceptible to teicoplanin (MIC, 0.5 μg/ml). The strains were distinct, were constitutively resistant via the synthesis of peptidoglycan precursors ending ind -alanyl-d -lactate, and harbored a chromosomalvanD gene cluster that was not transferable. New mutations were found in conserved domains of VanSD : at T170 I near the phosphorylation site in NEF1, at V67 A at the membrane surface in BM4653, at G340 S in the G2 ATP-binding domain in BM4655, in the F domain in BM4656 (a 6-bp insertion), and in the G1 and G2 domains of BM4654 (three mutations). The mutations resulted in constitutivity, presumably through the loss of the phosphatase activity of the sensor. The chromosomal Ddld -Ala:d -Ala ligase had an IS19 copy in NEF1, a mutation in the serine (S185 F) or near the arginine (T289 P) involved ind -Ala1 binding in BM4653 or BM4655, respectively, and a mutation next to the lysine (P180 S) involved ind -Ala2 binding in BM4654, leading to the production of an impaired enzyme. In BM4653vanYD , a new insertion sequence, ISEfa9 , belonging to the IS3 family, resulted in the absence ofd ,d -carboxypeptidase activity. Strain BM4656 had a functionald -Ala:d -Ala ligase, associated with high levels of both VanXD and VanYD activities, and is the first example of a VanD-type strain with a functional Ddl enzyme. Study of these five clinical isolates, displaying various assortments of mutations, confirms that all VanD-type strains isolated so far have undergone mutations in thevanSD orvanRD gene, leading to constitutive resistance, but that the Ddl host ligase is not always impaired. Based on sequence differences, thevanD gene clusters could be assigned to two subtypes:vanD-1 andvanD-4 .