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Antimicrobial Agents and Chemotherapy, September 2002, p. 3061-3064, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.3061-3064.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Efficacies of Quinupristin-Dalfopristin Combined with Vancomycin In Vitro and in Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus in Relation to Cross-Resistance to Macrolides, Lincosamides, and Streptogramin B- Type Antibiotics

Juliette Pavie,1 Agnès Lefort,1 Virginie Zarrouk,1 Françoise Chau,1 Louis Garry,1 Roland Leclercq,2 and Bruno Fantin1*

Institut National de la Santé et de la Recherche Médicale (EMI 9933), Faculté de Médecine Xavier Bichat, Paris ,1 Service de Microbiologie, Hôpital de la Côte de Nacre, Caen, France2

Received 27 December 2001/ Returned for modification 30 March 2002/ Accepted 6 May 2002


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ABSTRACT
 
A beneficial effect of the combination of quinupristin-dalfopristin and vancomycin was observed against two methicillin-resistant strains of Staphylococcus aureus harboring or not harboring the ermC gene, which codes for constitutive macrolide, lincosamide, and streptogramin B resistance. The beneficial effect was observed in time-kill studies, in which the drugs were used at inhibitory concentrations, and in a rabbit model of endocarditis, in which the combination was highly bactericidal and more active than monotherapies.


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TEXT
 
Methicillin-resistant Staphylococcus aureus (MRSA) represents a major cause of nosocomial infection, and glycopeptides remain the standard therapy for the treatment of systemic infections due to such strains. However, the emergence of MRSA strains with intermediate susceptibilities to glycopeptides (10, 15, 16) emphasizes the need for new therapeutic options that may include vancomycin in combination with another antibiotic.

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin that combines a type A streptogramin (dalfopristin) and a type B streptogramin (quinupristin). The combination of quinupristin and dalfopristin is synergistic (2) and is active in vitro against MRSA (1, 3, 4). However, most strains of MRSA are cross resistant to macrolide, lincosamide, and streptogramin B (MLSB)-type antibiotics by methylation of the ribosomal target. The expression of MLSB resistance is more frequently constitutive than inducible in MRSA (13). When it is constitutive, strains are resistant to quinupristin but remain susceptible to Q-D, although the bactericidal activity of Q-D is reduced in vitro and in vivo (8).

Therefore, the use of Q-D in combination with another antibiotic might be required for the treatment of severe infections due to strains resistant to quinupristin in order to increase the bactericidal activity and to prevent the emergence of resistance in vivo. Since Lorian et al. (14) have shown that Q-D at a subinhibitory dose produced thickening of the cell wall, it was suggested that a positive interaction could be observed between Q-D and cell wall-active agents. Indeed, a synergistic interaction has previously been reported between Q-D and ß-lactams in vitro and in vivo (17). The combination of Q-D and vancomycin against strains of MRSA might therefore be of clinical interest in order to increase the bactericidal activity of Q-D and to decrease the risk of emergence of resistance to both antibiotics since strains resistant to Q-D have been selected in vivo (18). Moreover, studies done in vitro (12) and in an infected fibrin clot model study (11) suggested the benefit of this combination. However, the susceptibilities of the study strains to MLSB antibiotics were not mentioned.

Two MRSA strains were evaluated in this study: HM1054, a clinical strain that is susceptible to quinupristin, and HM1054R, a strain that is resistant to quinupristin and that was obtained by conjugative transfer to HM1054 of the ermC gene, which codes for MLSB resistance (8). The two strains remained susceptible to Q-D (MIC, 1 µg/ml), whatever their profile of resistance to MLSB antibiotics (quinupristin MICs, 8 µg/ml for HM1054 and 64 µg/ml for HM1054R). The dalfopristin and vancomycin MICs for the two strains were 4 and 1 µg/ml, respectively.

Brain heart infusion (BHI) agar and broth (Difco, Detroit, Mich.) were used for all experiments. Quinupristin, dalfopristin, and Q-D were from by Aventis, Vitry sur Seine, France, and vancomycin was from Lilly, Saint-Cloud, France.

Time-kill studies were performed with overnight cultures diluted in fresh BHI broth to yield an inoculum of 106 CFU/ml. Antibiotics were used at concentrations achievable in human and rabbit sera (6, 8, 18). Q-D was used at concentrations of 1 and 4 µg/ml, and vancomycin was used at concentrations of 1, 8, and 32 µg/ml. After 0, 3, 6, and 24 h of incubation at 37°C, serial dilutions of 100-µl samples were subcultured and incubated 24 h at 37°C before the numbers of CFU were counted. Bactericidal activity was defined by a decrease in the original inoculum of at least 3 log10 CFU/ml.

Aortic endocarditis was induced in rabbits as described previously (18, 19). Twenty-four hours after catheter insertion, each rabbit was inoculated intravenously with 1 x 106 to 5 x 106 CFU of S. aureus in 1 ml of sterile saline. Untreated rabbits were killed at the start of therapy and served as control animals. For studies with strain HM1054, the killing of control animals and the start of therapy were performed 48 h after bacterial inoculation. For studies with strain HM1054R, this delay resulted in an extremely high concentration of bacteria in vegetations and the death of almost 80% of the rabbits before therapy was given. Therefore, in studies with this strain, the killing of control animals and the start of therapy were performed 36 h after inoculation of the bacteria. This resulted in comparable vegetation weights and bacterial concentrations in vegetations in the rabbits inoculated with the two strains (8).

The animals were treated intramuscularly for 4 days with one of the following regimens: Q-D at 30 mg/kg of body weight every 8 h, vancomycin at 50 mg/kg every 8 h, or the combination of Q-D and vancomycin, which were injected at two different sites. The Q-D dosing regimen provided areas under the curve for quinupristin and dalfopristin comparable to those achieved in humans after intravenous injection of 7.5 mg of Q-D/kg (6, 8). The vancomycin regimen produced peak (40 ± 8 µg/ml) and trough (12 ± 5 µg/ml) levels in serum comparable to those recommended for humans with severe infections (18).

The animals were killed 8 h after the last antibiotic injection, as described previously (8, 18). Vegetation homogenates were serially diluted and plated on agar to count the bacteria surviving after 24 h of incubation. To detect resistant mutants, vegetation homogenates were also plated on agar containing two- and fourfold the MIC of Q-D or vancomycin.

The comparisons of the treatment effects were performed by nonparametric one-way analysis of rank scores for several independent samples (the Kruskal-Wallis test), followed by the Mann-Whitney test to study differences between the means among the treatments for a given strain. The proportions of sterile rabbits were compared by the Fisher exact test.

Q-D at a concentration of 4 µg/ml and vancomycin at a concentration of 8 µg/ml were bactericidal against both strains (Fig. 1A and 1B). However, the bactericidal activity of Q-D against HM1054R was less than that against HM1054 (reductions of 3.0 and 4.9 log10 CFU/ml after 24 h of incubation, respectively). The combination of Q-D and vancomycin at a low concentration (1 µg/ml) was bactericidal against HM1054, producing a reduction of 3.9 log10 CFU/ml after 24 h of incubation, whereas treatment with Q-D alone achieved a reduction of only 1.5 log10 CFU/ml and treatment with vancomycin alone resulted in bacterial regrowth (Fig. 1A). The combination of Q-D and vancomycin at 1 µg/ml did not achieve bactericidal activity against HM1054R (a reduction of 2.4 log10 CFU/ml after 24 h of incubation) but was more active than monotherapies, as shown by a reduction of 0.7 log10 CFU/ml with Q-D after 24 h of incubation and bacterial regrowth with vancomycin after 24 h of incubation (Fig. 1B). The combination did not add any benefit to the monotherapies against the two strains when concentrations of Q-D or vancomycin higher than 1 µg/ml were used in the combination (data not shown) (9).



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  		FIG. 1. Time-kill experiments of the activities of Q-D at one and four times the MIC (Q-D1 and Q-D4, respectively) and vancomycin at one and eight times the MIC (Vm1 and Vm8, respectively) against S. aureus HM1054 (A) and S. aureus HM1054R (B). The MICs of Q-D and vancomycin for the two strains were each 1 µg/ml.

The activities of the different antibiotic regimens against experimental endocarditis are shown in Table 1. Q-D and vancomycin alone were bactericidal against HM1054 and displayed similar activities. The combination of Q-D and vancomycin was highly bactericidal, with a reduction of 8.2 log10 CFU/g of vegetation compared with the counts for the controls (P < 0.001), and was significantly more active than vancomycin or Q-D alone (P < 0.05). In addition, the combination sterilized 9 of 10 animals (90%), whereas the monotherapies sterilized 2 of 20 animals (10%) (P < 0.001).


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  		TABLE 1. Activities of vancomycin, Q-D, and their combination against two strains of S. aureus susceptible (HM1054) or resistant (HM1054R) to quinupristin after 4 days of treatment for rabbit endocarditis

Q-D and vancomycin were similarly active against HM1054R, as determined by the reduction in growth compared to the growth in the controls, although Q-D did not achieve bactericidal activity in vivo. The combination of Q-D and vancomycin was highly bactericidal, allowing a significant reduction of 5.5 log10 CFU/g of vegetation compared with the control growth (P < 0.001). The combination was more active than Q-D or vancomycin (P < 0.05) and sterilized 5 of 13 animals (38%), whereas the monotherapies sterilized 1 of 22 rabbits (4.5%) (P < 0.05).

No subpopulation with reduced susceptibility to Q-D or vancomycin was detected in vivo, regardless of the infecting strain and the regimen used.

In the present work, we report that the combination of Q-D and vancomycin is more active than monotherapies in vivo in a severe model of infection due to S. aureus strains with or without the constitutive MLSB resistance phenotype in terms of bactericidal activity and the rate of sterilization. This result correlated with those obtained by in vitro time-kill studies. Nevertheless, it is of major importance to underline the fact that this benefit was observed in vitro only with low concentrations of Q-D and vancomycin (e.g., concentrations that may be achieved in deep foci of infection such as cardiac vegetations) and not with concentrations of Q-D greater than the MIC (Fig. 1) (10).

We previously demonstrated that the penetration of quinupristin into vegetations is homogeneous, whereas dalfopristin showed a decreased concentration gradient between the periphery and the core of the vegetation (7). This result could explain why the addition of vancomycin to Q-D might allow an increased effect against both strains of bacteria localized in the core of the vegetation.

However, even if the benefit of the effect of the combination was similar against the two strains in vivo, the antibacterial effect of the combination was less pronounced against HM1054R than against HM1054 since both Q-D and vancomycin were less active against HM1054R than against HM1054. This result was expected for Q-D (8) but was not expected for vancomycin. The greater virulence of HM1054R may explain the in vivo phenotypic tolerance observed with vancomycin, as others have described previously (5).


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ACKNOWLEDGMENTS
 
We thank Aventis for technical assistance. Agnès Lefort received a grant from the Institut National de la Santé et de la Recherche Medicale.


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FOOTNOTES
 
* Corresponding author. Mailing address: Service de Médecine Interne, Hôpital Beaujon, 100 Blvd. du général Leclerc, 92118 Clichy Cedex, France. Phone: 01 40 87 58 90. Fax: 01 40 87 10 81. E-mail: bruno.fantin{at}bjn.ap-hop-paris.fr. Back


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REFERENCES
 
    1
  1. Aldridge, K., D. Schiro, and L. Varner. 1992. In vitro antistaphylococcal activity and testing of RP 59500, a new streptogramin, by two methods. Antimicrob. Agents Chemother. 36:854-855.[Abstract/Free Full Text]
    2. 2
  2. Bouanchaud, D. H. 1992. In vitro and in vivo synergistic activity and fractional inhibitory concentration of the components of a semi-synthetic streptogramin, RP 59500. J. Antimicrob. Chemother. 30:95-99.
    3. 3
  3. Brumfitt, W., J. M. T. Hamilton-Miller, and S. Shah. 1992. In vitro activity of RP 59500, a new semi-synthetic streptogramin antibiotic, against gram-positive bacteria. J. Antimicrob. Chemother. 30:29-37.
    4. 4
  4. Diekema, D. J., M. A. Pfaller, F. J. Schmitz, J. Smayevsky, J. Bell, R. N. Jones, and M. Beach. 2001. Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the Sentry antimicrobial surveillance program, 1997-1999. Clin. Infect. Dis. 32:S114-S132.
    5. 5
  5. Entenza, J. M., U. Fluckiger, M. P. Glauser, and P Moreillon. 1994. Antibiotic treatment of experimental endocarditis due to methicillin-resistant Staphylococcus epidermidis. J. Infect. Dis. 170:100-109.[Medline]
    6. 6
  6. Etienne, S. D., G. Montay, A. Le Liboux, A. Frydman, and J. J. Garaud. 1992. A phase I, double-blind, placebo-controlled study of the tolerance and pharmacokinetic behaviour of RP 59500. J. Antimicrob. Chemother. 30:123-131.
    7. 7
  7. Fantin, B., R. Leclercq, M. Ottaviani, J. M. Vallois, B. Maziere, J. Duval, J. J. Pocidalo, and C. Carbon. 1994. In vivo activities and penetration of RP 59500 in cardiac vegetations of experimental endocarditis. Antimicrob. Agents Chemother. 38:432-437.[Abstract/Free Full Text]
    8. 8
  8. Fantin, B., R. Leclerq, Y. Merlé, L. Saint Julien, C. Veyrat, J. Duval, and C. Carbon. 1995. Critical influence of resistance to streptogramin B type antibiotics on activity of RP 59500 (quinupristin-dalfopristin) in experimental endocarditis due Staphylococcus aureus. Antimicrob. Agents Chemother. 39:400-405.[Abstract/Free Full Text]
    9. 9
  9. Fuchs, P. C., A. L. Barry, and S. D. Brown. 2001. Interactions of quinupristin-dalfopristin with eight other antibiotics as measured by time-kill studies with 10 strains of Staphylococcus aureus for which quinupristin-dalfopristin alone was not bactericidal. Antimicrob. Agents Chemother. 45:2662-2665.[Abstract/Free Full Text]
    10. 10
  10. Hiramatsu, K., H. Hanaki, T. Ino, K. Yabuta, T. Oguri, and F. C. Tenover. 1997. Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility. J. Antimicrob. Chemother. 40:135-136.[Free Full Text]
    11. 11
  11. Kang, S., and M. Rybak. 1995. Pharmacodynamics of RP 59500 alone and in combination with vancomycin against S. aureus in an in vitro-infected fibrin clot model. Antimicrob. Agents Chemother. 39:1505-1511.[Abstract]
    12. 12
  12. Kang, S., and M. Rybak. 1997. In vitro bactericidal activity of RP 59500 (quinupristin/dalfopristin) alone and in combinations against resistant strains of Enterococcus species and Staphylococcus aureus. J. Antimicrob. Chemother. 39:33-39.[Abstract/Free Full Text]
    13. 13
  13. Lina, G., A. Quaglia, M. E. Reverdy, R. Leclercq, F. Vandenesch, and J. Etienne. 1999. Distribution of genes encoding resistance to macrolides, lincosamides, and streptogramins among staphylococci. Antimicrob. Agents Chemother. 43:1062-1066.[Abstract/Free Full Text]
    14. 14
  14. Lorian, V., Y. Esanu, and L. Amaral. 1994. Ultrastructure alterations of Staphylococcus aureus exposed to RP59500. J. Antimicrob. Chemother. 33:625-628.[Free Full Text]
    15. 15
  15. Ploy, M. C., C. Grelaud, C. Martin, L. de Lumbley, and F. Denis. 1998. First clinical isolate of vancomycin-intermediate Staphylococcus aureus in a French hospital. Lancet 351:1212.[Medline]
    16. 16
  16. Smith, T., M. L. Pearson, K. R. Wilcox, C. Cruz, M. V. Lancaster, B. Robinson-Dunn, F. C. Tenover, M. J. Zervos, J. Band, E. White, and W. R. Jarvis. 1999. Emergence of vancomycin resistance in Staphylococcus aureus. N. Engl. J. Med. 340:493-501.[Abstract/Free Full Text]
    17. 17
  17. Vouillamoz, J., J. M. Entenza, C. Feger, M. P. Glauser, and P. Moreillon. 2000. Quinupristin-dalfopristin combined with ß-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolides-lincosamides-streptogramin B Antibiotics. Antimicrob. Agents Chemother. 44:1789-1795.[Abstract/Free Full Text]
    18. 18
  18. Zarrouk, V., B. Bozdogan, R. Leclercq, L. Garry, C. Carbon, and B. Fantin. 2000. Influence of resistance to streptogramin A type antibiotics on the activity of quinupristin-dalfopristin in vitro and in experimental endocarditis due to Staphylococcus aureus. Antimicrob. Agents Chemother. 44:1168-1173.[Abstract/Free Full Text]
    19. 19
  19. Zarrouk, V., B. Bozdogan, R. Leclercq, L. Garry, C. Feger, C. Carbon, and B. Fantin. 2001. Activities of the combination of quinupristin-dalfopristin and rifampin in vitro and in experimental endocarditis due to Staphylococcus aureus strains with various phenotypes of resistance to macrolide-lincosamide-streptogramin antibiotics. Antimicrob. Agents Chemother. 45:1244-1248.[Abstract/Free Full Text]

Antimicrobial Agents and Chemotherapy, September 2002, p. 3061-3064, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.3061-3064.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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