ly-146032 and Endocarditis--Bacterial

Beta lactam agents are the most active drugs for the treatment of streptococci and methicillin-susceptible Staphylococcus aureus endocarditis. However, methicillin-resistant S. aureus (MRSA) is resistant to all beta lactam agents licensed to date, and alternative treatments are limited. Ceftobiprole is a novel broad-spectrum cephalosporin that binds with high affinity to PBP 2a, the penicillin binding protein that mediates the methicillin resistance of staphylococci and is active against MRSA. Ceftobiprole was compared to vancomycin, daptomycin, and linezolid in a rabbit model of MRSA aortic valve endocarditis caused by the homogeneously methicillin-resistant laboratory strain COL. Residual organisms in vegetations were significantly fewer in ceftobiprole-treated rabbits than in any other treatment group (P<0.05 for each comparison). In addition, the numbers of organisms in spleens and in kidneys were significantly lower in ceftobiprole-treated rabbits than in linezolid- and vancomycin-treated animals (P<0.05 for each comparison). Anti-MRSA beta lactam agents such as ceftobiprole may represent a significant therapeutic advance over currently available agents for the treatment of MRSA endocarditis.

Topics: Acetamides; Animals; Anti-Bacterial Agents; Cephalosporins; Chromatography, High Pressure Liquid; Daptomycin; Disease Models, Animal; Endocarditis, Bacterial; Linezolid; Methicillin-Resistant Staphylococcus aureus; Oxazolidinones; Rabbits; Random Allocation; Vancomycin

The mechanism(s) of daptomycin (DAP) resistance (DAPr) is incompletely defined. Thickened cell walls (CWs) acting as either a mechanical barrier or an affinity trap for DAP have been purported to be a major contributor to the DAPr phenotype. To this end, we studied an isogenic set of methicillin-resistant Staphylococcus aureus (MRSA) isolates (pulsotype USA 300) from the bloodstream of a DAP-treated patient with endocarditis in which serial strains exhibited increasing DAPr. Of interest, the DAPr isolate differed from its parental strain in several parameters, including acquisition of a point mutation within the putative synthase domain of the mprF gene in association with enhanced mprF expression, increased synthesis of lysyl-phosphotidylglycerol, an enhanced positive envelope charge, and reduced DAP surface binding. Transmission electron microscopy (TEM) revealed no significant increases in CW thickness in the two DAPr isolates (MRSA 11/21 and REF2145) compared with that in the DAP-susceptible (DAPs) parental strain, MRSA 11/11. The rates of Triton X-100-induced autolysis were also identical for the strain set. Furthermore, among six additional clinically isolated DAPs/DAPr S. aureus strain pairs, only three DAPr isolates exhibited CWs significantly thicker than those of the respective DAPs parent. These data confirm that CW thickening is neither universal to DAPr S. aureus nor sufficient to yield the DAPr phenotype among S. aureus strains.

Topics: Aminoacyltransferases; Anti-Bacterial Agents; Bacterial Proteins; Blood; Cell Wall; Daptomycin; Drug Resistance, Multiple, Bacterial; Endocarditis, Bacterial; Humans; Methicillin-Resistant Staphylococcus aureus; Microbial Sensitivity Tests; Microscopy, Electron, Transmission; Mutation; Octoxynol; Phenotype; Staphylococcal Infections

Daptomycin is approved for treatment of Staphylococcus aureus bacteremia and right-sided endocarditis. Increases in daptomycin MICs have been associated with failure. A rabbit model of aortic valve endocarditis was used to determine whether MIC correlates with activity in vivo and whether a higher daptomycin dose can improve efficacy. Two related clinical S. aureus strains, one with a daptomycin MIC of 0.5 microg/ml and the other with a MIC of 2 microg/ml, were used to establish aortic valve endocarditis in rabbits. Daptomycin was administered once a day for 4 days at 12 mg/kg of body weight or 18 mg/kg to simulate doses in humans of 6 mg/kg and 10 mg/kg, respectively. Endocardial vegetations, spleens, and kidneys were harvested and quantitatively cultured. The strain with a MIC of 2 microg/ml had a survival advantage over the strain with a MIC of 0.5 microg/ml with >100 times more organisms of the former in endocardial vegetations at the 12-mg/kg dose in a dual-infection model. Both the 12-mg/kg dose and the 18-mg/kg dose completely eradicated the strain with a MIC of 0.5 from vegetations, spleens, and kidneys. The 12-mg/kg dose was ineffective against the strain with a MIC of 2 in vegetations; the 18-mg/kg dose produced a reduction of 3 log(10) units in CFU in vegetations compared to the controls, although in no rabbit were organisms completely eliminated. Increasing the dose of daptomycin may improve its efficacy for infections caused by strains with reduced daptomycin susceptibility.

Topics: Animals; Anti-Bacterial Agents; Aortic Valve; Area Under Curve; Daptomycin; Disease Models, Animal; Dose-Response Relationship, Drug; Endocarditis, Bacterial; Heart Valve Diseases; Microbial Sensitivity Tests; Rabbits; Staphylococcal Infections; Staphylococcus aureus

Recently, the emergence of reduced susceptibility to daptomycin has been linked to the reduced vancomycin susceptibility that occurs after vancomycin exposure in Staphylococcus aureus in vivo and in vitro. This study evaluated this propensity in clinical isolates of S. aureus using an in vitro pharmacokinetic/pharmacodynamic model with simulated endocardial vegetations over 8 days. Five clinical isolates (four methicillin-resistant S. aureus isolates and one methicillin-susceptible S. aureus [MSSA] isolate), all of which were reported to have become nonsusceptible to daptomycin, were evaluated. The following regimens were evaluated: vancomycin 1 g every 12 h for 4 days followed by daptomycin 6 mg/kg of body weight daily for 4 days and daptomycin 6 mg/kg daily for 8 days. If nonsusceptibility was detected, the following regimens were evaluated: no treatment for 4 days followed by daptomycin 6 mg/kg daily for 4 days, vancomycin 1 g every 12 h for 4 days followed by daptomycin 10 mg/kg daily for 4 days, and daptomycin 10 mg/kg daily for 8 days. The emergence of daptomycin nonsusceptibility (12- to 16-fold MIC increase) was detected only with the MSSA isolate with daptomycin 6 mg/kg daily for 4 days after vancomycin exposure. However, the bactericidal activity of daptomycin was maintained and the MIC increases of these isolates, which had no mprF or yycG mutations, were unstable to serial passage on antibiotic-free agar. Subsequent regimens did not demonstrate nonsusceptibility to daptomycin. These findings suggest that reduced daptomycin susceptibility can be a strain-specific and unstable event. Further evaluation of the susceptibility relationship between daptomycin and vancomycin is necessary to understand the factors involved and their clinical significance.

Topics: Anti-Bacterial Agents; Culture Media; Daptomycin; Drug Therapy, Combination; Endocarditis, Bacterial; Humans; Methicillin; Methicillin Resistance; Microbial Sensitivity Tests; Models, Biological; Staphylococcus aureus; Vancomycin

Daptomycin is a lipopeptide antibiotic with potent in vitro activity against gram-positive cocci, including Staphylococcus aureus. This study evaluated the in vitro and in vivo efficacies of daptomycin against two clinical isolates: methicillin-resistant S. aureus (MRSA) 277 (vancomycin MIC, 2 microg/ml) and glycopeptide-intermediate S. aureus (GISA) ATCC 700788 (vancomycin MIC, 8 microg/ml). Time-kill experiments demonstrated that daptomycin was bactericidal in vitro against these two strains. The in vivo activity of daptomycin (6 mg/kg of body weight every 24 h) was evaluated by using a rabbit model of infective endocarditis and was compared with the activities of a high-dose (HD) vancomycin regimen (1 g intravenously every 6 h), the recommended dose (RD) of vancomycin regimen (1 g intravenously every 12 h) for 48 h, and no treatment (as a control). Daptomycin was significantly more effective than the vancomycin RD in reducing the density of bacteria in the vegetations for the MRSA strains (0 [interquartile range, 0 to 1.5] versus 2 [interquartile range, 0 to 5.6] log CFU/g vegetation; P = 0.02) and GISA strains (2 [interquartile range, 0 to 2] versus 6.6 [interquartile range, 2.0 to 6.9] log CFU/g vegetation; P < 0.01) studied. In addition, daptomycin sterilized more MRSA vegetations than the vancomycin RD (13/18 [72%] versus 7/20 [35%]; P = 0.02) and sterilized more GISA vegetations than either vancomycin regimen (12/19 [63%] versus 4/20 [20%]; P < 0.01). No statistically significant difference between the vancomycin HD and the vancomycin RD for MRSA treatment was noted. These results support the use of daptomycin for the treatment of aortic valve endocarditis caused by GISA and MRSA.

Topics: Animals; Anti-Bacterial Agents; Daptomycin; Disease Models, Animal; Endocarditis, Bacterial; Glycopeptides; Heart Valve Diseases; Humans; Methicillin Resistance; Microbial Sensitivity Tests; Models, Biological; Rabbits; Staphylococcal Infections; Staphylococcus aureus; Vancomycin; Vancomycin Resistance