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Comparison of the beta-lactamase gene cluster in clonally distinct strains of Enterococcus faecalis.

ABSTRACT: Ten beta-lactamase-producing Enterococcus faecalis isolates were examined for the presence of the staphylococcal beta-lactamase repressor and antirepressor genes. Four isolates, previously shown to be unrelated to each other by pulsed-field gel electrophoresis analysis, were positive for both genes by PCR, although beta-lactamase production was not induced with methicillin. Six isolates, previously shown to be clonally related, were negative for both genes by PCR. The blaZ sequences of eight beta-lactamase-producing E. faecalis isolates were determined. Seven isolates from five distinct clones had sequences identical to that previously reported for E. faecalis HH22, regardless of whether the repressor or antirepressor was demonstrated by PCR. However, blaZ from one isolate differed from those of the other enterococci by 11 nucleotides; this isolate is part of the large clone, as defined by pulsed-field gel electrophoresis and multilocus enzyme analysis, that includes HH22. These findings suggest either that enterococci have acquired the bla gene cluster from more than one source or that the gene cluster has undergone considerable change since acquisition by this clone.

SUBMITTER: Tomayko JF

PROVIDER: S-EPMC163285 | biostudies-other | 1996 May

REPOSITORIES: biostudies-other

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Comparison of the beta-lactamase gene cluster in clonally distinct strains of Enterococcus faecalis.

Tomayko J F JF Zscheck K K KK Singh K V KV Murray B E BE

Antimicrobial agents and chemotherapy 19960501 5

Ten beta-lactamase-producing Enterococcus faecalis isolates were examined for the presence of the staphylococcal beta-lactamase repressor and antirepressor genes. Four isolates, previously shown to be unrelated to each other by pulsed-field gel electrophoresis analysis, were positive for both genes by PCR, although beta-lactamase production was not induced with methicillin. Six isolates, previously shown to be clonally related, were negative for both genes by PCR. The blaZ sequences of eight bet ...[more]

PMID: 8723460

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Project description:We studied the clinical isolates Enterococcus faecium NEF1, resistant to high levels of vancomycin (MIC, 512 microg/ml) and teicoplanin (MIC, 64 microg/ml); Enterococcus faecium BM4653 and BM4656 and Enterococcus avium BM4655, resistant to moderate levels of vancomycin (MIC, 32 microg/ml) and to low levels of teicoplanin (MIC, 4 microg/ml); and Enterococcus faecalis BM4654, moderately resistant to vancomycin (MIC, 16 microg/ml) but susceptible to teicoplanin (MIC, 0.5 microg/ml). The strains were distinct, were constitutively resistant via the synthesis of peptidoglycan precursors ending in D-alanyl-D-lactate, and harbored a chromosomal vanD gene cluster that was not transferable. New mutations were found in conserved domains of VanS(D): at T(170)I near the phosphorylation site in NEF1, at V(67)A at the membrane surface in BM4653, at G(340)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 Ddl D-Ala:D-Ala ligase had an IS19 copy in NEF1, a mutation in the serine (S(185)F) or near the arginine (T(289)P) involved in D-Ala1 binding in BM4653 or BM4655, respectively, and a mutation next to the lysine (P(180)S) involved in D-Ala2 binding in BM4654, leading to the production of an impaired enzyme. In BM4653 vanY(D), a new insertion sequence, ISEfa9, belonging to the IS3 family, resulted in the absence of D,D-carboxypeptidase activity. Strain BM4656 had a functional D-Ala:D-Ala ligase, associated with high levels of both VanX(D) and VanY(D) 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 the vanS(D) or vanR(D) gene, leading to constitutive resistance, but that the Ddl host ligase is not always impaired. Based on sequence differences, the vanD gene clusters could be assigned to two subtypes: vanD-1 and vanD-4.

Dataset Information

Comparison of the beta-lactamase gene cluster in clonally distinct strains of Enterococcus faecalis.

Publications

Comparison of the beta-lactamase gene cluster in clonally distinct strains of Enterococcus faecalis.

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