Showing papers by "Barbara E. Murray published in 2002"

An Enterococcus faecalis ABC Homologue (Lsa) Is Required for the Resistance of This Species to Clindamycin and Quinupristin-Dalfopristin

Abstract: Enterococcus faecalis isolates are resistant to clindamycin (CLI) and quinupristin-dalfopristin (Q-D), and this is thought to be a species characteristic. Disruption of a gene ( abc-23 , now designated lsa , for “lincosamide and streptogramin A resistance”) of E. faecalis was associated with a ≥40-fold decrease in MICs of Q-D (to 0.75 μg/ml), CLI (to 0.12 to 0.5 μg/ml), and dalfopristin (DAL) (to 4 to 8 μg/ml) for the wild-type E. faecalis parental strain (Q-D MIC, 32 μg/ml; CLI MIC, 32 to 48 μg/ml; DAL MIC, 512 μg/ml). Complementation of the disruption mutant with lsa on a shuttle plasmid resulted in restoration of the MICs of CLI, Q-D, and DAL to wild-type levels. Under high-stringency conditions, lsa was found in 180 of 180 isolates of E. faecalis but in none of 189 other enterococci. Among 19 erm (B)-lacking Enterococcus faecium strains, 9 (47%) were highly susceptible to CLI (MIC, 0.06 to 0.25 μg/ml) and had DAL MICs of 4 to 16 μg/ml; for the remaining erm (B)-lacking E. faecium strains, the CLI and DAL MICs were 4 to >256 and 2 to >128 μg/ml, respectively. In contrast, none of 32 erm (B)-lacking E. faecalis strains were susceptible (CLI MIC range, 16 to 32 μg/ml; DAL MIC range, ≥32 μg/ml). When lsa was introduced into an E. faecium strain initially susceptible to CLI, the MICs of CLI and DAL increased ≥60-fold and that of Q-D increased 6-fold (to 3 to 6 μg/ml). Introduction of lsa into two DAL-resistant (MICs, >128 μg/ml), Q-D-susceptible (MICs, 0.5 and 1.5 μg/ml) E. faecium strains (CLI MICs, 12 and >256 μg/ml) resulted in an increase in the Q-D MICs from 3- to 10-fold (to 8 and >32 μg/ml), respectively. Although efflux was not studied, the similarity (41 to 64%) of the predicted Lsa protein to ABC proteins such as Vga(A), Vga(B), and Msr(A) of Staphylococcus aureus and YjcA of Lactococcus lactis and the presence of Walker A and B ATP-binding motifs suggest that this resistance may be related to efflux of these antibiotics. In conclusion, lsa appears to be an intrinsic gene of E. faecalis that explains the characteristic resistance of this species to CLI and Q-D.

Evidence that the enterococcal polysaccharide antigen gene (epa) cluster is widespread in Enterococcus faecalis and influences resistance to phagocytic killing of E. faecalis.

Abstract: In previous studies, we cloned a cluster of genes involved in polysaccharide biosynthesis (epa) from Enterococcus faecalis strain OG1RF and showed that this gene cluster mediated synthesis of a polysaccharide in Escherichia coli. Disruption of two open reading frames in the epa gene cluster of OG1RF generated two mutants, TX5179 and TX5180, which were attenuated in a mouse peritonitis model. In the current study, Western blotting was performed with serum from a patient with E. faecalis endocarditis and polysaccharide extracts from OG1RF and the mutants TX5179 and TX5180. OG1RF showed a smear in the high-molecular-weight region and discrete bands in the low-molecular-weight region, which were missing from the mutants; periodate treatment and carbohydrate staining confirmed the polysaccharide nature of this material. In a neutrophil killing assay using OG1RF-absorbed normal human serum, the mutants TX5179 and TX5180, respectively, were 50 and 2.4 times more susceptible to killing than wild-type OG1RF (P ≤ 0.01). With a fluorescence phagocytosis assay, 2.5 to 3 times more of the mutants were taken up by neutrophils than OG1RF (P ≤ 0.001). Finally, with restriction digestion and hybridization under high-stringency conditions, the epa gene cluster of OG1RF (which is also present in the sequenced E. faecalis strain V583) was detected in 12 of 12 other clonally distinct E. faecalis strains tested: a similar polysaccharide pattern was detected for the 12 strains on Western blots using an E. faecalis endocarditis patient serum, and sera from four other patients with E. faecalis endocarditis all reacted with polysaccharide extracts of OG1RF. These results indicate that the epa gene cluster is widespread among E. faecalis and confers some protection against human host defenses.

Molecular Typing of Selected Enterococcus faecalis Isolates: Pilot Study Using Multilocus Sequence Typing and Pulsed-Field Gel Electrophoresis

Abstract: The present study compared the recently developed multilocus sequence typing (MLST) approach with a well-established molecular typing technique, pulsed-field gel electrophoresis (PFGE), for subspecies differentiation of Enterococcus faecalis isolates. We sequenced intragenic regions of three E. faecalis antigen-encoding genes (ace, encoding a collagen and laminin adhesin; efaA, encoding an endocarditis antigen; and salA, encoding a cell wall associated antigen) and one housekeeping gene (pyrC) of 22 E. faecalis isolates chosen largely for their temporal and geographical diversity, but also including some outbreak isolates. MLST analysis of polymorphic regions of these four genes identified 13 distinct sequence types (STs) with different allelic profiles; the composite sequences generated from the four sequenced gene fragments of individual isolates showed 98.3 to 100% identity among the 22 isolates. We also found that the allelic profiles from two sequences, ace and salA, were sufficient to distinguish all 13 STs of this study. The 13 STs corresponded to 12 different PFGE types, with one previously designated PFGE clone (a widespread U.S. clone of β-lactamase-producing isolates) being classified into two highly related STs which differed at 2 of 2,894 bases, both in the same allele. MLST also confirmed the clonal relationships among the isolates of two other PFGE clonal groups, including vancomycin resistant isolates. Thus, this pilot study with representative E. faecalis isolates suggests that, similar to PFGE, the sequence-based typing method may be useful for differentiating isolates of E. faecalis to the subspecies level in addition to identifying outbreak isolates.