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PubMed1992

Influence of high-level gentamicin resistance and beta-hemolysis on susceptibility of enterococci to the bactericidal activities of ampicillin and vancomycin.

The bactericidal activities of ampicillin and vancomycin against 40 recent isolates of Enterococcus faecalis were examined by kill-kinetic studies at concentrations of 4 x the MIC and 20 micrograms/ml. Greater killing was seen with ampicillin (3.57 +/- 0.87 and 2.50 +/- 1.09 log10 CFU/ml, respectively; mean +/- standard deviation) than with vancomycin (1.23 +/- 0.65 and 1.05 +/- 0.57 log10 CFU/ml, respectively). Highly gentamicin-resistant strains showed a tendency toward reduced susceptibility to killing; beta-hemolytic strains were more susceptible than nonhemolytic strains when exposed to ampicillin at 20 micrograms/ml. Within each group, individual isolates demonstrated great variability in susceptibility to killing by the drugs.

Ampicillin↗
PubMed1992

Evidence for in vivo incorporation of D-lactate into peptidoglycan precursors of vancomycin-resistant enterococci.

The VanA ligase encoded by the vancomycin resistance plasmid pIP816 of Enterococcus faecium BM4147 condenses D-alanine with various D-2-hydroxy and D-2-amino acids in vitro. D-Lactate added to the culture medium restored the vancomycin resistance of a strain that does not produce the VanH dehydrogenase and therefore appears to be a substrate of VanA in vivo.

Drug Resistance, Microbial↗
PubMed1993

Antimicrobial susceptibilities of enterococci isolated from hospitalized patients.

One hundred and one isolates of Enterococcus species isolated recently from hospitalized patients were evaluated in vitro for antibiotic susceptibility. Teicoplanin and mideplanin were the most active agents, followed by ramoplanin, vancomycin, ciprofloxacin, ampicillin, and imipenem. High-level resistance to gentamicin (MIC > 500 micrograms/ml) and/or streptomycin (MIC > 2,000 micrograms/ml) was found in 60 isolates. High-level resistance to ampicillin (MIC > or = 16 micrograms/ml) was found in 17 isolates. MBC studies revealed that ramoplanin possesses significant bactericidal activity.

Anti-Bacterial Agents↗
PubMed1993

A gene conferring resistance to vancomycin but not teicoplanin in isolates of Enterococcus faecalis and Enterococcus faecium demonstrates homology with vanB, vanA, and vanC genes of enterococci.

We report the sequence of a 630-bp fragment of a gene associated with resistance to high levels of vancomycin in a clinical isolate of Enterococcus faecalis which retained susceptibility to teicoplanin. This gene was similar to the recently sequenced vanB and partially homologous with vanA, but it showed less-marked similarity to vanC. A DNA probe, derived from this polymerase chain reaction-amplified gene fragment, hybridized specifically with genomic DNA from Enterococcus faecium and E. faecalis isolates which were vancomycin resistant (MICs ranged from 8 to 512 micrograms/ml) but susceptible to teicoplanin. Curing of vancomycin resistance was associated with loss of DNA hybridization with the gene probe. Transfer of DNA which hybridized with the probe accompanied transfer of vancomycin resistance to a susceptible recipient strain. Neither curing nor transfer of vancomycin resistance was consistently related to loss or acquisition, respectively, of plasmid DNA.

Amino Acid Sequence↗
PubMed1994

Transferability and genetic relatedness of high-level gentamicin resistance among enterococci.

Gentamicin resistance in six enterococcal species was investigated. Transfer of resistance was observed for the donors E. faecium UC 79, E. avium CC 54, and E. gallinarum B 51, but not for E. raffinosus UC 78 or E. casseliflavus UC 73. Except for E. casseliflavus UC 73, homology was observed between the E. faecalis aac6'-aph2" gene and DNA from other species. Whereas 2.6-kb HindIII fragments encoded resistance in E. faecalis UC 244, its transconjugant, and E. raffinosus UC 78, 3.4-kb fragments encoded resistance in E. faecium UC 79, E. gallinarum B 51, and their transconjugants. A 3.4-kb fragment encoded resistance in E. avium CC 54, but 2.6-kb fragments encoded resistance in the transconjugants. Although many similarities were found among the strains, the heterogeneity in gentamicin resistance exhibited by some isolates indicates diversity among these determinants.

Blotting, Southern↗
PubMed1995

Heterogeneity of the vanA gene cluster in clinical isolates of enterococci from the northeastern United States.

In several strains of Enterococcus faecium isolated in Europe, the cluster of genes encoding high-level resistance to vancomycin (VanA phenotype) resides on a 10.85-kb transposon, Tn1546, or closely related elements. To determine whether Tn1546 was conserved in recent enterococcal isolates from the northeastern United States, seven strains were compared by restriction mapping and DNA hybridization with probes from within the van cluster. Two of the seven strains contained intact Tn1546-like sequences; however, in five of the strains, the organization of the van cluster differed from that of Tn1546. Three of the five strains with variations harbored a novel DNA segment within the van gene cluster. This 1,496-bp segment was similar to IS1165 of Leuconostoc mesenteroides and IS1181 of Staphylococcus aureus and was flanked by 24- and 23-bp imperfect inverted repeats and 8-bp direct repeats. On the basis of these findings, we propose that this element comprises a novel insertion-like sequence, IS1251. Multiple copies of IS1251 were also present at other sites in both resistant and susceptible clinical isolates. Our findings suggest that the van cluster in recent isolates from the northeastern United States differs from that present in the early European VanA phenotype strains.

Amino Acid Sequence↗
PubMed1996

Presence of vancomycin-resistant enterococci in farm and pet animals.

Enterococcus faecium strains with vanA-mediated glycopeptide resistance were isolated by enrichment culture from the intestines and feces of several animal species, mainly horses and dogs (8% positive), chickens (7% positive), and pigs (6% positive). Other vanA-positive enterococcal strains were identified as E. durans in gallinaceous birds, E. faecalis in a horse, and E. gallinarum in a pheasant. Samples from pigeons, cage birds, and ruminants were negative. It was concluded that vancomycin resistance is widespread among isolates from farm and pet animals.

Animals↗
PubMed1997

Antibiotic resistance among enterococci isolated from clinical specimens between 1953 and 1954.

Two hundred twenty group D streptococci isolated from 1953 to 1954 from patients in the Washington, D.C., area were characterized. All were susceptible to ampicillin, vancomycin, and gentamicin; none produced beta-lactamase activity. High-level resistance to streptomycin was expressed by 117 strains, and 2 strains were resistant to >8 microg of chloramphenicol per ml. Three isolates were resistant to both erythromycin and lincomycin, and DNA from these hybridized to an ermAM probe. Of 118 strains resistant to tetracycline and minocycline, genomic DNA from 63 was examined for homology to tet(M), tet(O), and tet(S). DNA from 20 strains hybridized to tet(M), DNA from 37 strains hybridized to tet(S), and DNA from none of the strains hybridized to tet(O).

Anti-Bacterial Agents↗
PubMed1999

Heterogeneity in the vanB gene cluster of genomically diverse clinical strains of vancomycin-resistant enterococci.

Molecular analysis of 17 genomically unrelated clinical VanB-type vancomycin-resistant enterococcus isolates from hospital patients in Germany, Norway, Sweden, the United Kingdom and the United States revealed three subtypes of the vanB gene cluster-vanB1, vanB2, and vanB3-which was in accordance with previous subtyping of the ligase gene sequence. There was no correlation between vanB subtype and levels of vancomycin resistance. All strains studied carried a structurally conserved vanB gene cluster as shown by long-range PCR (long PCR) covering 5,959 bp of the published sequence in vanB1 strain V583. Restriction analysis of long PCR amplicons displayed one unique vanB1 pattern and a second vanB2- and vanB3-specific pattern. The vanSB-vanYB intergenic sequences with flanking coding regions were identical within each vanB subtype with one exception. A U.S. vanB2 isolate had a 789-bp enlargement of this region containing a putative open reading frame (ORF) with substantial homology to an ORF in the Clostridium perfringens IS1469 insertion element. The molecular heterogeneity within the vanB gene cluster has implications for the selection of PCR primers, as the primers must ensure detection of all vanB subtypes, and is of importance when considering reservoirs and dissemination of vanB resistance. The molecular identity within the vanB1 and the vanB2 subtype indicates horizontal transmission of both gene clusters between isolates in different geographical areas. Restriction analysis of long PCR vanB amplicons may reveal specific varieties that can be used as epidemiological markers for mobile determinants conferring VanB-type resistance. The finding of three distinct vanB gene clusters should encourage a search for different environmental reservoirs of vanB resistance determinants.

Anti-Bacterial Agents↗
PubMed2000

In vivo activities of evernimicin (SCH 27899) against vancomycin-susceptible and vancomycin-resistant enterococci in experimental endocarditis.

To assess the potential efficacy of evernimicin (SCH 27899) against serious enterococcal infections, we used a rat model of aortic valve endocarditis established with either a vancomycin-susceptible Enterococcus faecalis or a vancomycin-resistant Enterococcus faecium strain. Animals infected with either one of the test strains were assigned to receive no treatment (controls) or 5-day therapy with one of the following regimens: evernimicin 60-mg/kg of body weight intravenous (i.v.) bolus once daily, 60-mg/kg i.v. bolus twice daily (b.i.d.), 60 mg/kg/day i.v. by continuous infusion, or 120 mg/kg/day i.v. by continuous infusion. These regimens were compared with vancomycin at 150 mg/kg/day. In animals infected with E. faecalis, evernimicin at 120 mg/kg/day by continuous infusion significantly reduced bacterial counts in vegetations (final density, 5.75+/-3.38 log(10) CFU/g) compared with controls (8.51+/-1.11 log(10) CFU/g). In animals infected with 0.5 ml of an 8 x 10(7)-CFU/ml inoculum of the vancomycin-resistant E. faecium, both 60-mg/kg bolus once a day and b.i.d. dose regimens of evernimicin were very effective (viable counts, 3.45+/-1.44 and 3.81+/-1.98 log(10) CFU/g, respectively). Vancomycin was unexpectedly active against infections induced with that inoculum. In animals infected with a 10(9)-CFU/ml inoculum of the vancomycin-resistant E. faecium, the evernimicin 60-mg/kg i.v. bolus b.i.d. reduced viable counts in vegetations compared with controls (6.27+/-1.63 versus 8.34+/-0.91 log(10) CFU/g; P<0.05), whereas vancomycin was ineffective. Although resistant colonies could be selected in vitro, we were not able to identify evernimicin-resistant clones from cardiac vegetations. An unexplained observation from these experiments was the great variability in final bacterial densities within cardiac vegetations from animals in each of the evernimicin treatment groups.

Aminoglycosides↗