Daptomycin is a cyclic lipopeptide derived

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1 Le Infezioni in Medicina, n. 2, , Articoli originali Original articles In vitro activity of daptomycin and comparator agents against Staphylococcus aureus isolates from intravenous drug users with right endocarditis Attività in vitro di daptomicina e altri antibiotici nei confronti di Staphylococcus aureus isolati da emocoltura di tossicodipendenti per via endovenosa affetti da endocardite del cuore destro Antonio Sanchez-Porto 1, Manuel Casanova-Roman 1, Javier Casas-Ciria 1, Maria Jose Santaella 1, Immaculada Sanchez-Morenilla 1, Jose Maria Eiros-Bouza 2 1 Department of Microbiology, Hospital of La Línea, Cádiz, Spain; 2 Department of Microbiology, University Hospital of Valladolid, Valladolid, Spain n INTRODUCTION Daptomycin is a cyclic lipopeptide derived from Streptomyces roseosporus as a fermentation product. Daptomycin s mechanism of action involves disruption of the bacterial cytoplasmic membrane, resulting in rapid depolarization. The depolarization of the membrane causes the immediate cessation of the biosynthesis of RNA, DNA and proteins and rapidly induces cell death [1]. The activity of daptomycin is dependent on physiological levels of free calcium ions (50 mg/l), which directly impacts the conditions required for in vitro susceptibility testing [2, 3]. Daptomycin has rapid concentration-dependent in vitro bactericidal activity against a wide spectrum of Gram-positive organism. This spectrum includes multidrug-resistant strains, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hvisa), for which there are very few therapeutic alternatives [4]. In this study, we evaluated the in vitro activity of daptomycin and several comparator agents tested against 33 nonduplicate clinical S. aureus isolates of intravenous drug users with right endocarditis. n MATERIAL AND METHODS Organism collection Tested strains were derived from blood cultures at La Linea Hospital (Cadiz, Spain). During the 7-year study period, 33 episodes of S. aureus right endocarditis were recorded in 33 intravenous drug users and the first isolated strains from them were stored at -80ºC. Bacterial species identification was based on standard clinical microbiological methods [5]. Susceptibility testing Strains were tested according to the Clinical and Laboratory Standards Institute (CLSI) broth microdilution methods [6]. Wider microdilution panels (Soria Melguizo, Madrid, Spain) were used for all the comparator agents and daptomycin supplemented with calcium (physiological level of 50 mg/l). Daptomycin was also tested using E-test strips which are also supplemented with calcium (AB Biodisk, Solna, Sweden). Daptomycin-susceptible breakpoint of 1 µg/ml was used. The categoric interpretations for all antibiotics were those of CLSI [7]. Methicillin resistance was determined by testing against cefoxitin disc diffusion test using a 30 µg 108

2 disc incubated at 30 C for 24 h on Mueller-Hinton agar. Erythromycin-resistant isolates were tested for inducible resistance using the D-zone method [7]. E-test strips (AB Biodisk, Solna, Sweden) were used to confirm the vancomycin MICs, according to the manufacturer s instructions. MRSA isolates with vancomycin MICs 2 µg/ml were screened using the E-test GRD Table 1 - Activities of daptomicyn and comparator agents against 33 S. aureus right endocarditis bloodstream isolates of injection drug users. No. of isolates and antimicrobial agent MIC (mg/l) No. and % susceptible Range 50% 90% strainsª Oxacillin susceptible (30) Daptomycin to % (30) Ciprofloxacin 0.25 to > % (26) Cotrimoxazole 1 to > % (30) Gentamicin 2 to > % (29) Erythromycin 0.25 to > > % (22) Clindamycin 0.5 to > % (29) Tetracycline 4 to > % (29) Chloramphenicol 8 to > % (29) Quinupristin-dalfopristin 0.25 to % (30) Rifampin % (30) Linezolid 0.25 to % (30) Teicoplanin 0.25 to % (30) Vancomycin 0.5 to % (30) Oxacillin resistant (3) Daptomycin to % (3) Ciprofloxacin >2 >2 >2 0% (0) Cotrimoxazole 1 to > % (2) Gentamicin >8 >8 >8 0% (0) Erythromycin >4 >4 >4 0% (0) Clindamycin 0.5 to >2 0.5 >2 66.6% (2) Tetracycline 4 to > % (2) Chloramphenicol 8 to > % (2) Quinupristin-dalfopristin 0.25 to > % (3) Rifampin 1 to % (3) Teicoplanin 0.5 to % (3) Linezolid 0.25 to % (3) Vancomycin % (3) ªMICs for susceptible isolates are those described in the CLSI. 109

3 (Glycopeptide Resistance Detection) (AB Biodisk, Solna, Sweden) to detect hvisa strains. The quality control strain S. aureus ATCC was tested along with every set of test. n RESULTS The results of in vitro susceptibility testing of S. aureus to the 14 antibiotics tested are shown in Table 1. Daptomycin was very active against MSSA and MRSA, with an MIC range of to 1 µg/ml. Daptomycin had an MIC 90 of 0.5 µg/ml for both groups. Vancomycin and linezolid had an MIC 90 of 2 µg/ml for MRSA. No vancomycin-resistant isolates were detected. Three MRSA isolates has a false vancomycin MIC >2 µg/ml determined by Wider microdilution panels; then, they were screened using the E-test GRD and resulted GRD negative. Thus, their final MIC was 2 µg/ml. Three MSSA isolates had a vancomycin MIC 90 of 2 µg/ml and four isolates of the same group had an MIC 90 of 1.5 µg/ml. Multidrug resistance (erythromycinciprofloxacin-gentamicin) was detected in 3 (100%) of the MRSA isolates. Regarding to daptomycin, Wider microdilution panels and E-test strips yielded the same results in all the isolates. n DISCUSSION S. aureus bacteremia is associated with serious complications, including endocarditis, in 30 to 40 percent of cases [8]. There is an increasing need for alternative agents in deep-seated infections, such as endocarditis, especially with the increasing incidence of VISA and hvisa. In the present study all our MRSA isolates tested were erythromycin-, ciprofloxacin-, and gentamicin-resistant. Our data has not shown resistance to linezolid. The emergence of linezolidresistant S. aureus has been associated with prolonged treatment and suboptimal dosage [9]. The treatment of serious MRSA infections continues to be challenging. Vancomycin has been the preferred antimicrobial agent to treat such MRSA infections [10]. However, vancomycin treatment failure is not uncommon, even when MRSA strains are fully susceptible to vancomycin (MIC 2 µg/ml). Soriano et al. [11] showed that vancomycin cannot be considered an optimal option for treatment of S. aureus bacteremia due to strains with vancomycin MICs >1 µg/ml. We found that all (three) MRSA isolates and three MSSA isolates had an MIC of 2 µg/ml. Four MSSA isolates had an MIC of 1.5 µg/ml. Daptomycin is highly bactericidal against all S. aureus isolates, including wild-type, VISA and hvisa [12]. An in vitro model with simulated endocardial vegetations demonstrated that daptomycin 6 mg/kg once daily achieved 99.9% kill (defined as a 3 log 10 CFU/g reduction in colony count from the initial inoculum) of high-inoculum MRSA within 36 h [13]. Daptomycin has a bactericidal activity, in the absence of cell proliferation, which may be valuable against slow-growing or growth-arrested gram-positive organisms. Miró et al. evaluated the in vitro activity of daptomycin plus or minus gentamicin or rifampin in a rabbit model of infective endocarditis by simulating human pharmacokinetics. Daptomycin plus gentamicin was as effective as daptomycin alone in reducing the density of bacteria in valve vegetations (0 [0-2]) log CFU/g veg; P=0.83), and both were more effective than daptomycin plus rifampin (3 [2-3.5] log CFU/g veg; P<0.05) for the strain studied. They haven t found statistical difference between daptomycin plus gentamicin and daptomycin alone for MRSA treatment [14]. Our data show that daptomycin was highly active against the S. aureus endocarditis bloodstream isolates tested, and that all isolates were inhibited at the susceptibility breakpoint of 1 µg/ml. Our data are consistent with that observed for European, North American and Spanish isolates [15-17]. Interestingly, it has been recognized that there is a correlation between reduced daptomycin susceptibility and vancomycin resistance in VISA. It has been postulated that the mechanism of the loss of daptomycin susceptibility is due to the inability to pass through the physical barrier of the enlarged cell wall [18]. Gallon et al. communicated that daptomycin showed lower MIC 90 levels compared to vancomycin, teicoplanin, and linezolid (0.19 µg/ml vs. 2, 1.5, and 1 µg/ml, respectively), irrespective of oxacillin susceptibility. So, they concluded that as with linezolid, daptomycin seems to constitute an alternative option to treat some staphylococcal infections in the context of high oxacillin resistance prevalence and high glycopeptides MIC [19]. Mortality rates of patients with left-sided MRSA endocarditis may be as high as 70%. Prosthetic endocarditis and denial of surgery when indicated are associated with a worse prognosis. On the other hand, right sided MRSA endocarditis 110

4 is less frequent and affects intravenous drug users. It is more frequent community acquired and the prognosis is better, with a 15% mortality rate [20]. The duration of parenteral antibiotic treatment in right sided endocarditis is between 4 to 6 weeks [21]. A shorter 2 weeks treatment has been suggested for selected cases of rightsided involvement with a good prognosis [22]. In our study, most of the patients, intravenous drug users, were HIV-infected on prophylaxis depending CD4 count and almost all of them were on antibiotic prophylaxis. Hepatitis B and C, tuberculosis and oesophageal candidiasis were frequent comorbidities. At the beginning of the study period, the incidence of all MRSA isolates in our hospital was a 20% and a 10% for bacteraemia. Nowadays, the picture is quite different; we have a 28% of MRSA isolates and for bacteraemia the incidence is a 20%. In conclusion, our findings and those of other in vitro studies suggest that daptomycin and linezolid could be viable options for treatment of right endocarditis and bacteraemia caused by S. aureus, MRSA and hvisa. Key words: daptomycin, endocarditis, Staphyococcus aureus. Financial support: No support was received. Conflict of interest: There is no conflict of interest SUMMARY There is an increasing need for alternative agents in endocarditis, especially with the increasing incidence of vancomycin-intermediate Staphylococcus aureus (VISA). We evaluated the in vitro activity of daptomycin and several comparator agents against 33 non-duplicate clinical Staphylococcus aureus isolates from intravenous drug users with right endocarditis. Wider microdilution panels were used for all the comparator agents and daptomycin. Daptomycin was also tested using E-test strips. E-test strips were used to confirm the vancomycin MICs. Methicillin-resistant Staphylococcus aureus (MRSA isolates with vancomycin MICs 2 g/ml were screened using the E-test GRD. In all, 30 isolates were methicillin-susceptible (MSSA) and 3 MRSA. The three MRSA isolates exhibited a false vancomycin MIC >2 g/ml determined by Wider microdilution panels. They were screened using the E-test GRD and they were GRD negative. Their final MIC was 2 g/ml. Three MSSA and three MRSA isolates had a vancomycin MIC of 2 g/ml. Four MSSA isolates had a vancomycin MIC of 1.5 g/ml, daptomycin MIC g/ml, linezolid MIC 90 2 g/ml. As regards daptomycin, wider microdilution panels and E-test strips yielded the same results. Our findings suggest that daptomycin and linezolid are a viable alternative for treating right endocarditis and bacteraemia caused by MSSA, MRSA and hvisa RIASSUNTO Background: Nella terapia dell endocardite si ravvisa la necessità crescente di opzioni terapeutiche alternative, soprattutto alla luce dell aumentata incidenza di ceppi di Staphylococcus aureus caratterizzati da sensibilità intermedia a vancomicina (VISA). Nel presente studio l attività in vitro di daptomicina e diversi altri comparatori è stata valutata nei confronti di 33 isolati clinici, non duplicati, di Staphylococcus aureus provenienti da pazienti, tossicodipendenti per via endovenosa, affetti da endocardite del cuore destro. Materiali e metodi: L attività di tutti gli antibiotici in studio è stata determinata mediante test di microdiluizione in brodo (Wider) ma daptomicina è stata testata anche mediante E-test. La conferma dei valori di MIC di vancomicina è stata effettuata mediante E-test. Lo screening dei ceppi di S. aureus meticillino-resistenti (MR- SA) con MIC di vancomicina 2 µg/ml è stato effettuato utilizzando l E-test GRD. Risultati: Dei 33 isolati, 30 sono risultati meticillinosensibili (MSSA) e 3 meticillino-resistenti. Per tre isolati MRSA è stato riscontrato, con il sistema di microdiluizione Wider, un falso valore di MIC di vancomicina >2 µg/ml, poi confutato dall E-test GRD. Il reale valore di MIC di questi ceppi era pari a 2 µg/ml. Vancomicina ha evidenziato un valore di MIC pari a 2 µg/ml per tre MSSA e tre MRSA. Per quattro MSSA, i valori di MIC di vancomicina sono risultati pari a 1,5 µg/ml, la MIC 90 di daptomicina pari a 0,25 µg/ml, e quella di linezolid pari a 2 µg/ml. Il sistema di microdiluizione Wider ha rilevato, per daptomicina, valori identici a quelli osservati con l E-test. Conclusioni: I nostri riscontri suggeriscono che daptomicina e linezolid costituiscono una valida alternativa per il trattamento dell endocardite del cuore destro e della batteriemia che riconoscano una eziologia da MSSA, MRSA e hvisa. 111

5 n REFERENCES [1] Eisenstein B.I. Lipopeptides, focusing on daptomycin, for the treatment of gram-positive infections. Expert Opin. Investig. Drugs 13, , [2] Fuchs P.C., Barry A.L., Brown S.D. Daptomycin susceptibility tests: interpretative criteria, quality control, and effect of calcium on in vitro tests. Diagn. Microbiol. Infect. Dis. 38, 51-58, [3] Jevitt L.A., Thorne G.M., Traczewski M.M., et al. Multicenter evaluation of the E-test and Disk Diffusion methods for differentiating daptomycin-susceptible from non-daptomycin-susceptible Staphylococcus aureus isolates. J. Clin. Microbiol. 44 (9), , [4] Streit J.M., Jones R.N., Sader H.S. Daptomycin activity and spectrum: a worldwide sample of 6737 clinical Gram-positive organisms. J. Antimicrob. Chemother. 53, , [5] Bannerman T.L., Peacock S.J Staphylococcus, Micrococcus, and other catalase-positive cocci that grow aerobically. In: Murray RM, Barron EJ, Jorgensen JH, Landry ML, Pfaller MA, editors. Manual of Clinical Microbiology. Washington DC: ASM Press. p [6] Clinical and Laboratory Standards Institute. Methods for dilution antimicrobial susceptibility test for bacteria that grow aerobically; approved standard, 7 th edition, M7-A7. Wayne, PA: CLSI; [7] Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing, 18 th informational supplement, M100-S18. Wayne, PA: CLSI; [8] Fowler V.G. Jr, Miro J.M., Hoen B., et al. Staphylococcus aureus endocarditis: a consequence of medical progress. JAMA 293, , [9] Gales A.C., Sader H.S., Andrade S.S., Lutz L., Machado A., Barth A.L. Emergence of linezolid-resistant Staphylococcus aureus during treatment of pulmonary infection in a patient with cystic fibrosis. Int. J. Antimicrob. Agents 27, , [10] Fowler V.G. Jr, Boucher H.W., Corey R., et al. Daptomycin versus standard therapy for bacteremia and endocarditis caused by Staphylococcus aureus. N. Engl. J. Med. 335, , [11] Soriano A., Marco F., Martinez J.A., et al. Influence of vancomycin minimum inhibitory concentration on the treatment of methicillin-resistant Staphylococcus aureus bacteremia. Clin. Infect. Dis. 46, , [12] Sader H.S., Fritsche T.R., Jones R.N. Daptomycin bactericidal activity and correlation between disk and broth microdilution method results in testing of Staphylococcus aureus strains with decreased susceptibility to vancomycin. Antimicrob. Agents Chemother. 50, , [13] Tsuji B.T., Rybak M.J. Short-course gentamicin in combination with daptomycin or vancomycin against Staphylococcus aureus in an in vitro pharmacodynamic model with simulated endocardial vegetations. Antimicrob. Agents Chemother. 49, , [14] Miro J.M., García de la Maria C., Armero Y., et al. The addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in the treatment of experimental endocarditis due to methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother Jul 20. [Epub ahead of print]. [15] Sader H.S., Streit J.M., Fritsche T.R., Jones R.N. Antimicrobial susceptibility of gram-positive bacteria isolated from European medical centres: results of the Daptomycin Surveillance Programme ( ). Clin. Microbiol. Infect. 12, , [16] Castanheira M., Jones R.N., Sader H.S. Update of the in vitro activity of daptomycin tested against 6710 Gram-positive cocci isolated in North America. Diagn. Microbiol. Infect. Dis. 61, , [17] Picazo J.J., Betriu C., Culebras E., Rodriguez- Avial I., Gomez M., Lopez F. Activity of daptomycin against staphylococci collected from bloodstream infections in Spanish medical centers. Diagn. Microbiol. Infect. Dis. 64, , [18] Cui L., Tominaga E., Neoh H.M., Hiramatsu K. Correlation between reduced daptomycin susceptibility and vancomycin resistance in vancomycin-intermediate Staphylococcus aureus. Antimicrob. Agents Chemother. 50, , [19] Gallon O., Guillet-Caruba C., Lamy B., Laurent F., Doucet-Populaire F., Decousser J.W. In vitro activity of daptomycin against Staphylococci isolated from bacteremia and community-onset skin and soft tissue infections in France: data from two nationwide studies. Eur. J. Clin. Microbiol. Infect. Dis Jun 6. [Epub ahead of print]. [20] Garau J., Bouza E., Chastre J., Gudiol F., Harbarth S. Management of methicillin-resistant Staphylococcus aureus infections. Clin. Microbiol. Infect 15, , [21] Baddour L.M., Wilson W.R., Bayer A.S., et al. Infective endocarditis: diagnosis, antimicrobial therapy, and management of complications: a statement for healthcare professionals from the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease in the Young, and the Councils on Clinical Cardiology, Stroke, and Cardiovascular Surgery and Anesthesia, American Heart Association: endorsed by the Infectious Diseases Society of America. Circulation 111, e , [22] Torres-Tortosa M., de Cueto M., Vergara A., et al. Prospective evaluation of a two-week course of intravenous antibiotics in intravenous drug addicts with infective endocarditis. Eur. J. Clin. Microbiol. Infect. Dis. 13, ,