Bacteria In Vegetations Research Articles

Daptomycin Is Effective for Treatment of Experimental Endocarditis Due to Methicillin-Resistant and Glycopeptide-Intermediate Staphylococcus epidermidis

This study evaluated the daptomycin activity against two methicillin-resistant Staphylococcus epidermidis (MRSE) clinical isolates with different vancomycin susceptibilities: MRSE-375, with a vancomycin MIC of 2 microg/ml, and NRS6, a glycopeptide-intermediate S. epidermidis (GISE) strain with a vancomycin MIC of 8 microg/ml. The in vivo activity of daptomycin at two different doses (standard dose [SD-daptomycin], 6 mg/kg of body weight/day intravenously [i.v.]; high dose [HD-daptomycin], 10 mg/kg/day i.v.) was evaluated in a rabbit model of infective endocarditis and compared with that of a standard dose of vancomycin (SD-vancomycin; 1 g i.v. every 12 h) for 2 days. For the MRSE-375 strain, high-dose vancomycin (HD-vancomycin; 1 g i.v. every 6 h) was also studied. For MRSE-375, SD- and HD-daptomycin therapy sterilized significantly more vegetations than SD-vancomycin therapy (9/15 [60%] and 11/15 [73%] vegetations, respectively, versus 3/16 [19%] vegetations; P = 0.02 and P = 0.002, respectively). HD-daptomycin sterilized more vegetations than HD-vancomycin (11/15 [73%] versus 5/15 [33%] vegetations; P = 0.03) and was more effective than SD- and HD-vancomycin in reducing the density of bacteria in valve vegetations (0 log(10) CFU/g vegetation [interquartile range {IQR}, 0 to 1 log(10) CFU/g vegetation] versus 2 log(10) CFU/g vegetation [IQR, 2 to 2 log(10) CFU/g vegetation] and 2 log(10) CFU/g vegetation [IQR, 0 to 2.8 log(10) CFU/g vegetation]; P = 0.002 and P = 0.01, respectively). For the NRS6 strain, SD- and HD-daptomycin were significantly more effective than vancomycin in reducing the density of bacteria in valve vegetations (3.7 log(10) CFU/g vegetation [IQR, 2 to 6 log(10) CFU/g vegetation] versus 7.1 log(10) CFU/g vegetation [IQR, 5.2 to 8.5 log(10) CFU/g vegetation]; P = 0.02). In all treatment arms, isolates recovered from vegetations remained susceptible to daptomycin and vancomycin and had the same MICs. In conclusion, daptomycin at doses of 6 mg/kg/day or 10 mg/kg/day is more effective than vancomycin for the treatment of experimental endocarditis due to MRSE and GISE.

Addition of Gentamicin or Rifampin Does Not Enhance the Effectiveness of Daptomycin in Treatment of Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus

This study evaluated the activity of daptomycin combined with either gentamicin or rifampin against three methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates in vitro and one isolate in vivo against a representative strain (MRSA-572). Time-kill experiments showed that daptomycin was bactericidal against these strains at concentrations over the MIC. Daptomycin at sub-MIC concentrations plus gentamicin at 1x and 2x the MIC yielded synergy, while the addition of rifampin at 2 to 4 microg/ml resulted in indifference (two strains) or antagonism (one strain). The in vivo activity of daptomycin (6 mg/kg of body weight once a day) was evaluated +/- gentamicin (1 mg/kg intravenously [i.v.] every 8 h [q8h]) or rifampin (300 mg i.v. q8h) in a rabbit model of infective endocarditis by simulating human pharmacokinetics. Daptomycin plus gentamicin (median, 0 [interquartile range, 0 to 2] log10 CFU/g vegetation) was as effective as daptomycin alone (0 [0 to 2] log10 CFU/g vegetation) in reducing the density of bacteria in valve vegetations (P = 0.83), and both were more effective than daptomycin plus rifampin (3 [2 to 3.5] log10 CFU/g vegetation; P < 0.05) for the strain studied. In addition, daptomycin sterilized a ratio of vegetations that was similar to that of daptomycin plus gentamicin (10/15 [67%] versus 9/15 [60%]; P = 0.7), and both regimens did so more than daptomycin plus rifampin (3/15 [20%]; P = 0.01 and P = 0.02, respectively). No statistical difference was noted between daptomycin plus gentamicin and daptomycin alone for MRSA treatment. In the combination arm, all isolates from vegetations remained susceptible to daptomycin, gentamicin, and rifampin. Sixty-one percent of the isolates (8/13) acquired resistance to rifampin during monotherapy. In the daptomycin arm, resistance was detected in only one case, in which the daptomycin MIC rose to 2 microg/ml among the recovered bacteria. In conclusion, the addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in the treatment of experimental endocarditis due to MRSA.

Efficacy of Daptomycin in Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus is becoming increasingly prevalent as both a nosocomial and a community-acquired pathogen. Daptomycin, a lipopeptide antibiotic now in phase III clinical trials, is rapidly bactericidal in vitro against a range of gram-positive organisms, including methicillin-resistant S. aureus (MRSA). In this study, we compared the efficacy of daptomycin with that of vancomycin, each with or without rifampin, in a model of experimental aortic valve endocarditis due to MRSA. The infecting strain (MRSA strain 32) was susceptible to daptomycin (MIC = 1 micro g/ml), vancomycin (MIC = 0.5 micro g/ml), and rifampin (MIC = 0.5 micro g/ml). Daptomycin was administered at 25 or 40 mg/kg q24h (q24h) by subcutaneous injection in an attempt to simulate human doses of 4 and 6 mg/kg q24h, respectively. Vancomycin was given at 150 mg/kg q24h by continuous intravenous infusion. Rifampin was given at 25 mg/kg by intramuscular injection q24h. Treatment was started 6 h postinoculation and continued for 4.5 days. Outcome was assessed by counting the residual viable bacteria in vegetations. The mean peak daptomycin levels in serum at 2 h after subcutaneous administration of 25 and 40 mg/kg were 64 and 91 micro g/ml, respectively. Daptomycin was undetectable in serum at 24 h. The total exposure was comparable to that achieved clinically in humans receiving the drug. Bacterial counts (mean log(10) number of CFU per gram +/- the standard deviation) in untreated controls reached 10.6 +/- 0.8. In treated rats, bacterial counts were as follows: vancomycin, 7.1 +/- 2.5; daptomycin at 25 mg/kg, 5.5 +/- 1.7; daptomycin at 40 mg/kg, 4.2 +/- 1.5. The difference between daptomycin at 40 mg/kg and vancomycin at 150 mg/kg was statistically significant (P = 0.004). In the study of combination therapy, vegetation bacterial counts were as follows: daptomycin at 40 mg/kg, 4.6 +/- 1.6; rifampin, 3.6 +/- 1.3; vancomycin plus rifampin, 3.3 +/- 1.1; daptomycin plus rifampin, 2.9 +/- 0.8. The difference between daptomycin and daptomycin plus rifampin was statistically significant (P = 0.006). These results support the continued evaluation of daptomycin for serious MRSA infections, including infective endocarditis.

Activity of Isepamicin and Selection of Permeability Mutants to -Lactams during Aminoglycoside Therapy of Experimental Endocarditis Due to Klebsiella pneumoniae CF104 Producing an Aminoglycoside Acetyltransferase 6' Modifying Enzyme and a TEM-3 -Lactamase

The pharmacokinetics and efficacy of isepamicin were compared with those of amikacin and gentamicin in a rabbit model of endocarditis due to Klebsiella pneumoniae CF104 producing beta-lactamase TEM-3 and aminoglycoside acetyltransferase AAC(6')-IV. Only isepamicin and gentamicin, alone or combined with ceftriaxone, were effective as determined by titration of viable bacteria in vegetations. Variants highly resistant to ceftriaxone without change in MICs of aminoglycosides were isolated at the end of each therapeutic regimen except with the most effective one (ceftriaxone plus gentamicin). Examination of the bacterial outer membrane proteins as well as the 50% inhibition of the beta-lactamase activity in intact and sonified cells suggested a permeability defect as being responsible for the increased MICs of ceftriaxone. The activity of isepamicin was superior to that of amikacin against the TEM-3-AAC(6')-IV-producing strain. The combination of gentamicin plus ceftriaxone was the most effective regimen in terms of efficacy and prevention of emergence of resistant strains. Suboptimal aminoglycoside monotherapy might be responsible for selection of permeability mutants to beta-lactams.

Comparison of ampicillin-sulbactam with vancomycin for treatment of experimental endocarditis due to a beta-lactamase-producing, highly gentamicin-resistant isolate of Enterococcus faecalis

Increasing antibiotic resistance in the enterococci, including the capacity for beta-lactamase production and the development of high-level aminoglycoside resistance, has complicated the treatment of serious enterococcal infections, which often require synergistic antibiotic combinations for cure. We utilized the rabbit model of aortic valve endocarditis to investigate the effects of various antibiotics, alone and in combination, against a multiply antibiotic-resistant isolate of Enterococcus faecalis. Female New Zealand White rabbits were infected with either a beta-lactamase-producing, gentamicin-resistant isolate of E. faecalis or a non-beta-lactamase-producing, aminoglycoside-susceptible isolate, and the mean log10 CFU per gram of vegetation were determined. The most active agents were low-dose ampicillin-sulbactam (200 mg/kg of body weight per day), high-dose ampicillin-sulbactam (400 mg/kg of body weight per day), and vancomycin (150 mg/kg of body weight per day), which reduced the titers of bacteria by 2.27, 2.76, and 2.85 log10 (CFU/g, respectively, compared with controls. While ampicillin-sulbactam and vancomycin were equally efficacious in reducing titers of bacteria in vegetations, no animals were cured (defined as < 2 log10 CFU/g of vegetation) by either agent, whether treatment was continued for 3 or 7 days. The addition of gentamicin was not associated with increased killing in rabbits infected with the aminoglycoside-resistant isolate. Both high-dose ampicillin-sulbactam and vancomycin regimens demonstrated significant, continued reduction in bacterial titers with the longer periods of treatment (P < or = 0.05); 7-day treatment with high-dose ampicillin-sulbactam produced a greater reduction in bacterial titers in vegetation than 7-day treatment with vancomycin (P < or = 0.05). We conclude that ampicillin-sulbactam and vancomycin are equally effective in the treatment of experimental endocarditis due to beta-lactamase-producing, highly gentamicin-resistant E. faecalis. The optimum therapy for such infections in humans is not known.

Relative efficacies of broad-spectrum cephalosporins for treatment of methicillin-susceptible Staphylococcus aureus experimental infective endocarditis

The effects of treatment with broad-spectrum parenterally administered cephalosporins and cefuroxime, cefazolin, or nafcillin were compared in an experimental model of Staphylococcus aureus infective endocarditis, and the results in vivo were compared with the activities of the study drugs in vitro. After 3 days of treatment, all antimicrobial agents tested were more effective than no treatment in reducing the number of surviving bacteria in cardiac valve vegetations. Nafcillin was the most effective agent studied and was significantly more active than was ceftizoxime, ceftriaxone, cefotaxime, cefoperazone, cefuroxime, or cefazolin (P < or = 0.05). Cefpirome and ceftazidime were the most effective broad-spectrum cephalosporins. The outcome of treatment with cefpirome or ceftazidime was similar to that of treatment with nafcillin and significantly better than that of treatment with ceftizoxime or cefotaxime (P < or = 0.05). Treatment outcome correlated closely with the MICs of the antimicrobial agents for the study strain with the exception of ceftazidime, which was significantly more active in vivo in comparison with other agents than predicted by its MIC (P < or = 0.0003). When ceftazidime was excluded as an outlier, treatment outcome correlated with the MICs of the remaining study drugs (Spearman's correlation coefficient, 0.95; P < or = 0.0004), as well as with the estimated percentage of time during which the concentration of total drug (correlation coefficient, -0.85; P < or = 0.007) or free drug (correlation coefficient, -0.90; P < or = 0.003) exceeded the MIC. A consideration of total or free drug concentrations in relation to MICs did not significantly improve the correlation with outcome observed with the MICs alone.

Efficacy of ticarcillin-clavulanic acid for treatment of experimental Staphylococcus aureus endocarditis in rats.

The efficacy of ticarcillin-clavulanic acid was compared with the efficacies of standard antistaphylococcal agents (flucloxacillin, oxacillin, nafcillin, and vancomycin) and ticarcillin in an experimental model of Staphylococcus aureus endocarditis. Therapy was either initiated soon (8 h) after infection, when numbers of bacteria in aortic valve vegetations were relatively low (approximately 6 to 8 log10 CFU/g), or delayed until 24 h after infection, when the vegetations usually contained greater than 9 log10 CFU/g. Doses of the antibiotic were selected to produce peak concentrations in rat serum similar to those achievable in humans after administration of parenteral therapeutic doses. Ticarcillin-clavulanic acid was more effective overall than ticarcillin alone against endocarditis caused by beta-lactamase-producing strains of S. aureus, illustrating the beta-lactamase-inhibitory activity of clavulanic acid in vivo. Ticarcillin-clavulanic acid was as effective as the standard antistaphylococcal beta-lactam agents flucloxacillin, oxacillin, and nafcillin in these infections, whereas vancomycin was generally less active. These results illustrate the clinical potential of ticarcillin-clavulanic acid in the prophylaxis or therapy of severe staphylococcal infections.

Influence of Staphylococcus aureus antibody on experimental endocarditis in rabbits.

To evaluate the potential protective benefit of antibody to whole cells of Staphylococcal aureus for the prevention of endocarditis, the rabbit endocarditis model was used. Methicillin-sensitive (17A) and methicillin-resistant (173) S. aureus strains were evaluated in rabbits with or without indwelling intracardiac catheters. All immunized rabbits developed significant homologous agglutinating antibody titers (the mean reciprocal titers were 15,300 to strain 17A and 1,150 to strain 173). After challenge, virtually no significant differences were observed between immunized and unimmunized animals with respect to (i) incidence of endocarditis, (ii) concentration of bacteria in infected vegetations, (iii) incidence of metastatic renal abscesses, or (iv) concentrations of bacteria in infected kidneys. The clearance of homologous S. aureus strains from blood cultures was similar for immunized and unimmunized animals at 10 to 90 min after intravenous challenge. In vivo adherence of homologous S. aureus strains to aortic valves and vegetations was similar in immunized and unimmunized animals when evaluated at 30 and 90 min postchallenge. Even without catheterization, the incidence of bacteremia and renal abscesses was the same in immunized and unimmunized rabbits. Whole-cell-induced S. aureus antibody did not prevent or modify any stage in the development of endocarditis in rabbits.

Teicoplanin and rifampicin singly and in combination in the treatment of experimental Staphylococcus epidermidis endocarditis in the rabbit model.

Teicoplanin and rifampicin were evaluated as single and combined agents in the treatment of endocarditis due to Staphylococcus epidermidis in the rabbit model. Rabbits were treated for ten days and the number of bacteria in vegetations determined. At the end of ten days the geometric mean number of bacteria in the vegetations were 5.53 X 10(8), 6.68 X 10(6). 1.10 X 10(4), 2.57 X 10(1) cfu/g of vegetation for control, teicoplanin, rifampicin, and teicoplanin plus rifampicin groups respectively. The MIC and MBC values of the S. epidermidis isolates were 0.78 mg/l for teicoplanin and less than or equal to 0.10 mg/l for rifampicin. In the rifampicin treated group three post-treatment isolates of S. epidermidis tested exhibited marked resistance to rifampicin with MIC and MBC values greater than or equal to 200 mg/l. Teicoplanin and rifampicin were both effective as single agents in the clearance of S. epidermidis from the bloodstream. Rifampicin was more effective than teicoplanin in the clearance of S. epidermidis from vegetations but teicoplanin in combination with rifampicin was more effective than either drug alone.

Tissue factor is a major stimulus for vegetation formation in enterococcal endocarditis in rabbits.

We examined the possible mechanisms of local initiation of coagulation in vegetation formation in enterococcal endocarditis by using a rabbit model. Contact activation and tissue factor expression by freshly excised aortic valves were assessed using assays developed for use with cultured cells. Bacteria alone lacked procoagulant activity and contact activation of plasma by excised valves did not occur. 4-d infected but not control valves expressed significant tissue factor activity (231 +/- 17 mU vs. 51 +/- 7 SE), which did not correlate with numbers of bacteria in vegetations. Tissue factor activity was also present in valves from rabbits infected for 1 and 2 d, as well as those from granulocytopenic and monocytopenic animals. Our findings suggest that tissue factor, expressed by host cells in response to infection, is a major stimulus for fibrin deposition in vegetation development.

Therapy for experimental endocarditis due to Staphylococcus epidermidis.

Vancomycin was evaluated with and without gentamicin and/or rifampin in therapy for endocarditis due to methicillin-resistant Staphylococcus epidermidis in rabbits. Vancomycin (30 mg/kg iv every 12 hr), gentamicin (3.5 mg/kg im every 8 hr), rifampin (20 mg/kg im every 12 hr), combinations of vancomycin plus gentamicin, vancomycin plus rifampin, and vancomycin plus gentamicin plus rifampin were injected for two days, and the number of bacteria in vegetations was determined. Ratios of minimal inhibitory concentrations to minimal bactericidal concentrations (microgram/ml) for S. epidermidis were 3.1:25 for vancomycin, 0.2:0.8 for gentamicin, and 0.4:0.4 for rifampin. After two days of therapy, mean log colony-forming units +/- SD in vegetations were 7.1 +/- 1.5 (none of eight animals were sterile) for vancomycin; 4.6 +/- 2.2 (two of nine) for gentamicin; 4.5 +/- 2.2 (two of eight) for rifampin; 3.3 +/- 1.3 (three of 10) for vancomycin plus gentamicin; 2.7 +/- 1.2 (three of nine) for vancomycin plus rifampin; 2.1 +/- 0.2 (eight of nine) for vancomycin plus gentamicin plus rifampin; and 8.1 +/- 1.3 (none of 12) for the control group. Gentamicin, rifampin, vancomycin plus gentamicin, and vancomycin plus rifampin were significantly more effective than was vancomycin; vancomycin plus rifampin was more effective than was gentamicin alone; and the combination of vancomycin plus gentamicin plus rifampin was more effective than were the drugs administered alone or in the combinations vancomycin plus gentamicin and vancomycin plus rifampin. Two days of treatment followed by seven days of no treatment resulted in 71%, 29%, and 14% sterile vegetations in rabbits receiving the combination therapy vancomycin plus gentamicin plus rifampin, vancomycin plus rifampin, and vancomycin plus gentamicin, respectively.

Antibiotic therapy of experimental Staphylococcus epidermidis endocarditis.

Endocarditis was produced in rabbits with a methicillin-resistant Staphylococcus epidermidis isolate. Subpopulations resistant to other semisynthetic penicillins and cephalosporins were detected in the isolate. Their presence was probably responsible for the increase in minimum bactericidal concentrations and minimum inhibitory concentrations when tests with high inocula, rather than low inocula were pursued. Rabbits were treated for either 2 or 7 days with nafcillin, cephalothin, cefamandole, vancomycin, rifampin, or gentamicin. Spontaneous death was uncommon in either controls (84% survival) or treated animals (80 to 94% survival). There was no significant difference in the number of bacteria in vegetations of rabbits treated for 7 days with cephalothin, cefamandole, nafcillin, or no antibiotic (control). There was a significant reduction in total bacteria in vegetations of rabbits given vancomycin, gentamicin, or rifampin for 7 days as compared with cephalothin, cefamandole, nafcillin or control. Gentamicin or rifampin sterilized significantly more vegetations after 7 days than cephalothin, cefamandole, nafcillin, or control; rifampin was more effective in sterilizing vegetations than either gentamycin or vancomycin after 2 days. Mutants resistant to 10 mug of rifampin per ml comprised the total bacterial population cultured from vegetations of 2 of 17 rabbits treated with this antibiotic for 7 days; there was no change in the susceptibility of vegetation isolates to other antibiotics. Rifampin, vancomycin, or gentamicin may prove to be more effective in humans than cephalosporins or semisynthetic penicillins in the treatment of methicillin-resistant S. epidermidis endocarditis.