Institute of Medical Microbiology, University of Münster Hospital and Clinics, 48149 Münster, Germany
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Abstract |
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Introduction |
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The ketolides are a new class of macrolide antibiotics with a keto group replacing the L-cladinose moiety in position 3 and an alkyl-aryl extension at positions 11 and 12 of the lactone ring. The ketolides have activity against a broad range of pathogens, particularly against all major respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis.5,6 However, data on the activity of ABT-773 against staphylococci are limited.
The aims of this study were: (i) to evaluate the activity of ABT-773 against a large number of different and well-characterized staphylococcal species, particularly against clonally different methicillin-resistant strains isolated from several geographical locations in Germany, including strains expressing different macrolide-lincosamide-streptogramin B (MLSB) resistance phenotypes; and (ii) to compare the in vitro anti-staphylococcal activity of this novel ketolide with the macrolides erythromycin and clarithromycin.
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Materials and methods |
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As MRSA may cause outbreaks, we used several other criteria to avoid including multiple isolates of the same strain: first, isolates were collected over a period of years, which would make a single clone unlikely. Secondly, isolates were collected from different geographical locations in Germany, which would also reduce the chance of obtaining a single clone, and finally, when S. aureus isolates with similar antibiograms and phenotypes were obtained, we carried out pulsed-field gel electrophoresis (PFGE) and selected only one example of each strain.
The 179 S. aureus strains included 32 penicillinsusceptible S. aureus (PSSA), 63 methicillin-susceptible S. aureus (MSSA) and 84 MRSA. The 157 coagulasenegative staphylococci (CoNS) comprised 41 methicillin-susceptible and 26 methicillin-resistant Staphylococcus epidermidis strains, 23 methicillin-susceptible and 32 methicillin-resistant Staphylococcus haemolyticus strains, and 35 other CoNS belonging to the following species: seven Staphylococcus hominis, six Staphylococcus saprophyticus, six Staphylococcus warneri, four Staphylococcus cohnii, three Staphylococcus lugdunensis, three Staphylococcus simulans, two Staphylococcus xylosus, two Staphylococcus sciuri, one Staphylococcus capitis and one Staphylococcus hyicus.
The staphylococci were identified from a variety of conventional phenotypic characteristics and by using the API-Staph system (ATB32 Staph; bioMérieux, Marcy lÉtoile, France). To test for inducible and constitutive expression of macrolide-lincosamide (ML) resistance, the disc diffusion test was carried out as defined classically using erythromycin (15 µg) and clindamycin (10 µg) discs (Oxoid Ltd, Basingstoke, UK) without delineating subdivisions.3 For this purpose, an aqueous suspension of bacterial growth from blood agar was adjusted to McFarland 0.5, and inoculated by swab on MuellerHinton agar (Difco, Augsburg, Germany). The arrangement of the discs allowed both the susceptibility pattern to individual compounds and interactions between both antibiotics to be observed with a minimal amount of repetition. As described previously, zones were interpreted according to their size and shape as indicating susceptible or resistant, the latter being inducible if a D-shaped zone was observed (the compound on the left being the inducer).3 Isolates were confirmed to be methicillin resistant by supplementation of the agar with 2% NaCl (using 5 µg oxacillin discs results were read after incubation for 48 h at 30°C) and by detection of the mecA gene in strains with non-definable resistance phenotype as reported previously.9
The MICs were determined on MuellerHinton agar, using the agar dilution technique with a final inoculum of c. 104 per spot. The following antimicrobial agents were used and obtained from their respective manufacturers: ABT-773, erythromycin, clarithromycin, quinupristindalfopristin. With the exception of quinupristindalfopristin, the compounds were tested in 13 different concentrations ranging from 0.031 to 128 mg/L. Quinupristindalfopristin was tested in eight different concentrations ranging from 0.06 to 8 mg/L. The results were read after 18 h incubation at 36°C. The following reference strains were included as controls: S. aureus ATCC 25923, ATCC 29213, ATCC 43300; Enterococcus faecium ATCC 51599; Escherichia coli ATCC 35218; Pseudomonas aeruginosa ATCC 27853. Additionally, sterility and growth controls were always carried out.
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Results |
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Discussion |
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In this context, the ability of the ketolide ABT-773 to inhibit staphylococci with an inducible MLSB resistance phenotype may be of major clinical importance. All strains that were clindamycin susceptible or showed the inducible type of MLSB resistance were inhibited by 0.063 mg/L of ABT-773, irrespective of the methicillin resistance phenotype.
In previous studies testing the activity of ABT-773 against staphylococci, multiple isolates of the same strain were not excluded by phenotypic or genomic typing. In addition, isolates were not classified previously regarding their MLSB phenotype.5,12,13 Thus, our results for methicillin-resistant strains differ from those of previous investigations in which methicillin-susceptible strains (MIC90S 0.030.06 mg/L) were generally found to be more susceptible to ABT-773 than methicillin-resistant strains (MIC90S >16128 mg/L).5,13 In our study, we tested a large number of clonally unrelated strains. This is particularly important for MRSA, which often cause at least regional outbreaks with the same strain. Furthermore, a broad spectrum of different, well-defined staphylococcal species was included in the testing.
Overall, the newly developed agent ABT-773 was highly active against both methicillin-susceptible and resistant strains with inducible MLSB resistance, stimulating further evaluation of these agents for therapy of infections due to staphylococci. However, strains with constitutive type of MLSB resistance are not in the spectrum of this ketolide. Therefore, an accurate knowledge of the local susceptibility pattern will be necessary if ABT-773 is to be used as empirical therapy for infections thought to be caused by multi-resistant S. aureus.
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Acknowledgements |
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Notes |
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References |
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2 . Paradisi, F., Corti, G. & Messeri, D. (2001). Antistaphylococcal (MSSA, MRSA, MSSE, MRSE) antibiotics. Medical Clinics of North America 85, 117. [ISI][Medline]
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.
Hamilton-Miller, J. M. & Shah, S. (2000). Patterns of phenotypic resistance to the macrolide-lincosamide-ketolide-streptogramin group of antibiotics in staphylococci. Journal of Antimicrobial Chemotherapy 46, 9419.
4 . Fridkin, S. K. (2001). Vancomycin-intermediate and -resistant Staphylococcus aureus: what the infectious disease specialist needs to know. Clinical Infectious Diseases 32, 10815. [ISI][Medline]
5
.
Andrews, J. M., Weller, T. M., Ashby, J. P., Walker, R. M. & Wise, R. (2000). The in vitro activity of ABT773, a new ketolide antimicrobial agent. Journal of Antimicrobial Chemotherapy 46, 101722.
6 . Barrett, J. F. & Dougherty, T. J. (2001). ABT-773: a new ketolide antibiotic. Expert Opinion on Investigational Drugs 10, 34351. [ISI][Medline]
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.
Von Eiff, C., Reinert, R. R., Kresken, M., Brauers, J., Hafner, D. & Peters, G. for the Multicenter Study on Antibiotic Resistance in Staphylococci and other Gram-Positive Cocci Study (MARS) Group. (2000). Nationwide German multicenter study on prevalence of antibiotic resistance in staphylococcal bloodstream isolates and comparative in vitro activities of quinupristindalfopristin. Journal of Clinical Microbiology 38, 281923.
8
.
Von Eiff, C., Becker, K., Machka, K., Stammer, H. & Peters, G. for the Study Group. (2001). Nasal carriage as a source of Staphylococcus aureus bacteremia. New England Journal of Medicine 344, 116.
9 . Murakami, K., Minamide, W., Wada, K., Nakamura, E., Teraoka, H. & Watanabe, S. (1991). Identification of methicillin-resistant strains of staphylococci by polymerase chain reaction. Journal of Clinical Microbiology 29, 22404. [ISI][Medline]
10
.
Lowy, F. D. (1998). Staphylococcus aureus infections. New England Journal of Medicine 339, 52032.
11 . Moellering, R. C., Jr (1998). Problems with antimicrobial resistance in Gram-positive cocci. Clinical Infectious Diseases 26, 11778. [ISI][Medline]
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.
Goldstein, E. J., Citron, D. M., Merriam, C. V., Warren, Y. & Tyrrell, K. (2000). Comparative in vitro activities of ABT-773 against aerobic and anaerobic pathogens isolated from skin and soft-tissue animal and human bite wound infections. Antimicrobial Agents and Chemotherapy 44, 25259.
13 . Barry, A. L., Brown, S. D. & Fuchs, P. C. (2000). Antimicrobial activity of ABT-773. In Program and Abstracts of the Fifth International Conference on the Macrolides, Azalides, Streptogramins, Ketolides and Oxazolidinones, Seville, Spain, 2000. Abstract 2.12, p. 24. ICMAS, Inc., Atlanta, GA.
Received 28 March 2001; returned 20 July 2001; revised 28 August 2001; accepted 25 September 2001