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Efficacy of daptomycin in the treatment of experimental endocarditis due to susceptible and multidrug-resistant enterococci.

OBJECTIVES: Daptomycin was tested in vitro and in rats with experimental endocarditis against the ampicillin-susceptible and vancomycin-susceptible Enterococcus faecalis JH2-2, the vancomycin-resistant (VanA type) mutant of strain JH2-2 (strain JH2-2/pIP819), and the ampicillin-resistant and vancomycin-resistant (VanB type) Enterococcus faecium D366. METHODS: Rats with catheter-induced aortic vegetations were treated with doses simulating intravenously kinetics in humans of daptomycin (6 mg/kg every 24 h), amoxicillin (2 g every 6 h), vancomycin (1 g every 12 h) or teicoplanin (12 mg/kg every 12 h). Treatment was started 16 h post-inoculation and continued for 2 days. RESULTS: MICs of daptomycin were 1, 1 and 2 mg/L, respectively, for strains JH2-2, JH2-2/pIP819 and D366. In time-kill studies, daptomycin showed rapid (within 2 h) bactericidal activity against all strains. Daptomycin was highly bound to rat serum proteins (89%). In the presence of 50% rat serum, simulating free concentrations, daptomycin killing was maintained but delayed (6-24 h). In vivo, daptomycin treatment resulted in 10 of 12 (83%), 9 of 11 (82%) and 11 of 12 (91%) culture-negative vegetations in rats infected with strains JH2-2, JH2-2/pIP819 and D366, respectively (P < 0.001 compared to controls). Daptomycin efficacy was comparable to that of amoxicillin and vancomycin for susceptible isolates. Daptomycin, however, was significantly (P < 0.05) more effective than teicoplanin against the glycopeptide-susceptible strain JH2-2 and superior to all comparators against resistant isolates. CONCLUSIONS: These results support the use of the newly proposed daptomycin dose of 6 mg/kg every 24 h for treatment of enterococcal infections in humans.

Amoxicillin↗

Analysis of bacteriolytic activity patterns, a novel approach to the taxonomy of enterococci.

The bacteriolytic activities of different group D streptococcal species on various media and substrates were studied. Our results showed that all of the enterococcal species which we tested had bacteriolytic activity on at least one of the media used, while the group D nonenterococcal species had no such activity. In addition, using culture media containing different additives and different pH values, we defined seven major groups of bacteriolytic activity (lyogroups), each of which overlapped with one species (four lyogroups), two species (two lyogroups), or four species (one lyogroup). The detection of enterococcal lyogroups proved to be as reliable for species identification as the conventional methods presently in use.

Bacteriolysis↗

Antibiotic resistance patterns of enterococci isolated from coastal bathing waters.

Recreational water should be considered a risk for enterococcal infections in regions with high utilisation and long exposure periods. A total of 1113 enterococcal isolates was obtained from 1670 bathing water samples from 120 bathing areas of seven prefectures in northern Greece. Enterococcus avium, E. raffinosus and E. faecium were the most prevalent species. Single, double and multiple antibiotic resistance patterns were observed in 33.5% 31.0% and 22.8% of the isolates, respectively. Resistance to erythromycin occurred most frequently, in 57.3% isolates, many of which also exhibited resistance to ciprofloxacin and rifampicin as well as high-level resistance to kanamycin and streptomycin. The results suggest that bathing water may contribute to the dissemination of uncommon enterococcal species that exhibit resistance to several antibiotics which are used to treat community-acquired infections.

Anti-Bacterial Agents↗

Use of penicillin-binding proteins for the identification of enterococci.

The results of 20 physiological and fermentation tests and examination of the penicillin-binding proteins (PBPs) of 85 enterococcal strains demonstrated that the genus Enterococcus could be divided into at least nine distinct species: E. faecalis, E. faecium, E. durans, E. hirae, E. avium, E. gallinarum, E. casseliflavus, E. malodoratus and E. mundtii. Each species had a specific pattern of at least five PBPs, with molecular masses in the range of about 40-130 kDa. The pattern of PBPs may be useful for identification purposes, since some strains with unusual fermentation characteristics were assigned to species by this technique.

Bacterial Proteins↗

Transferable resistance and aminoglycoside-modifying enzymes in enterococci.

Ten isolates of Streptococcus faecalis and two isolates of S. faecium were studied together with an NCTC strain of each species. Antibiotic susceptibility tests showed different patterns of high-level resistance to aminoglycosides. Three S. faecalis strains were highly resistant to gentamicin and other aminoglycosides. By means of a filter membrane technique, transfer of high-level resistance to aminoglycosides was demonstrated from S. faecalis to S. faecalis, from S. faecium to S. faecalis and from S. faecalis to S. faecium, the last of which has not previously been described. Aminoglycoside-modifying enzymes were assayed with radiolabelled cofactors. High-level resistance to gentamicin and other aminoglycosides could be attributed to the production of 2''-O-phosphotransferases, 3'-O-phosphotransferases, 6-O-adenylyltransferases and 6'-N-acetyltransferases. Other resistance mechanisms accounted for resistance in two strains of S. faecalis and one strain of S. faecium that were highly resistant only to streptomycin and one S. faecalis strain that was moderately resistant to all aminoglycosides. A low level of 6'-N-acetyltransferases was detected in the three strains of S. faecium but this did not confer high-level resistance to aminoglycosides and this trait could not be transferred.

Acetyltransferases↗

Regulated interactions between partner and non-partner sensors and response regulators that control glycopeptide resistance gene expression in enterococci.

Transcription of the vanA and vanB glycopeptide resistance gene clusters is regulated by the VanRS and VanRBSB two-component regulatory systems, respectively. Histidine to glutamine substitutions were introduced at positions 164 of VanS and 233 of VanSB to prevent autophosphorylation of the sensor kinases and transfer of the phosphate groups to the VanR and VanRB response regulators. VanSH164Q and VanSBH233Q abolished activation of VanR and VanRB by host kinases. The phosphatase activity of VanSBH233Q was negatively modulated by vancomycin whereas VanSH164Q prevented transcription of the resistance genes under all growth conditions. Cross-talk was detected between VanRB and VanS in a vanSB null mutant. VanR is required for activation of promoters PR and PH allowing transcription of the regulatory (vanRS) and resistance (vanHAXYZ) genes, respectively. Under non-inducing conditions, activation of VanR by cross-talk was blocked by the presence of a multicopy plasmid carrying PH. Presence of the high-affinity VanR-binding sites of the regulatory region of PH on the multicopy vector probably sequestered VanR, thereby preventing autoactivation of the PR promoter. Under such circumstances, stimulation of the host kinase by glycopeptides or moenomycin was required for expression of the resistance genes.

Anti-Bacterial Agents↗