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Antimicrobial Agents and Chemotherapy, August 2006, p. 2875-2879, Vol. 50, No. 8
0066-4804/06/$08.00+0 doi:10.1128/AAC.00286-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
R. M. Alden Research Laboratory, Santa Monica, California 90404,1 David Geffen School of Medicine at UCLA, Los Angeles, California 900732
Received 6 March 2006/ Returned for modification 5 April 2006/ Accepted 3 May 2006
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ABSTRACT |
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0.125 µg/ml against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and 120 anaerobes (Clostridium perfringens, other clostridia, Peptoniphilus asaccharolyticus, Finegoldia magna, and Anaerococcus prevotii), compared to respective MIC90s for MSSA and MRSA of 0.5 and 1 µg/ml for vancomycin, 4 and 4 µg/ml for linezolid, 0.5 and 0.5 µg/ml for daptomycin, and 0.25 and >8 µg/ml for clindamycin. |
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14.5 million Americans by 2010 (8), and diabetic foot infections (DFIs) account for 20% of all hospitalizations of diabetic patients (1). DFIs are often multibacterial with aerobic and anaerobic bacteria. Recently, community-acquired methicillin-resistant Staphylococcus aureus (MRSA) (2, 3, 14) has accounted for 50% of all S. aureus skin and skin structure infection (SSTI) isolates (2, 3, 14). Previously, we noted (6) that MRSA was isolated from 20% of DFIs. As a reference lab for a DFI study, we received 473 pretreatment specimens, of which 91.3% grew aerobic bacteria, including 48% that grew S. aureus as one of the isolates (one-quarter of which were MRSA), and 41.6% grew anaerobes, with anaerobic gram-positive cocci the most common isolates.
Dalbavancin (BI397) is new glycopeptide (4, 10) with good activity against gram-positive organisms, including MRSA, but none against gram-negative organisms (13, 19). Dalbavancin has a long elimination half-life (8.5 days) and has been effective in treating gram-positive SSTIs (9, 18) with a two-dose regimen. For DFIs, an antimicrobial agent with a long half-life, especially one administered once weekly, seems to be advantageous.
Specimens were obtained from patients with clinical infection who had not received antimicrobials within 48 h and after wound debridement. To avoid bias, 329 consecutively isolated gram-positive aerobic and anaerobic organisms were selected for this study. Isolates were identified by standard criteria (12, 15) and stored in skim milk at –70°C. Frozen anaerobic cultures were subcultured twice onto brucella agar supplemented with hemin, vitamin K1, and 5% sheep blood (Anaerobe Systems, Morgan Hill, CA) to ensure purity and good growth. Aerobic strains were subcultured to Trypticase soy blood agar. Susceptibility testing was performed according to CLSI (formerly NCCLS) standards M11-A6 (17) and M7-A6 (16).
The types and numbers of strains tested are shown in Table 1. Laboratory-standard reference powders were either obtained from their manufacturers or purchased from Sigma Chemicals (St. Louis, MO).
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Aerobic organisms were tested by the broth microdilution method using cation-adjusted Mueller-Hinton broth, with 2.5% lysed horse blood supplementation for the streptococci and corynebacteria. Dalbavancin was tested separately in dry-format trays prepared by TREK Diagnostics (Cleveland, OH) and provided by Vicuron (now Pfizer, Inc., New York, NY). The trays containing the remaining antimicrobials were prepared in house with serial twofold dilutions of test drugs using the Quick-Spense apparatus (Sandy Springs Instrument Co., Germantown, MD). Daptomycin tests were supplemented with additional Ca2+ to 50 mg/liter. The trays were stored at –70°C until used. Enterococcus faecalis ATCC 29212 and S. aureus ATCC 29213 were tested simultaneously.
The in vitro activities of dalbavancin and 12 comparator agents are shown in Table 1. Dalbavancin had an MIC90 of 0.125 µg/ml against methicillin-susceptible S. aureus (MSSA) and MRSA isolates. Other MIC90s for MSSA and MRSA, respectively, were 0.5 and 1 µg/ml for vancomycin, 4 and 4 µg/ml for linezolid, 0.5 and 0.5 µg/ml for daptomycin, and 0.25 and >8 µg/ml for clindamycin. The MIC of dalbavancin for one of three strains of Staphylococcus haemolyticus was 2 µg/ml. To determine if this was peculiar to the species, we tested 16 additional strains and found the range to be 0.06 to 0.125 µg/ml. Against Streptococcus agalactiae, Streptococcus pyogenes, and group G beta-hemolytic streptococci, dalbavancin had an MIC90 of 0.125 µg/ml. Dalbavancin inhibited Corynebacterium amycolatum and Corynebacterium jeikeium strains at 1 µg/ml and was active against 120 anaerobes (Clostridium perfringens, other clostridia, Peptoniphilus asaccharolyticus, Finegoldia magna, Anaerococcus prevotii, and other anaerobic gram-positive cocci), with MIC90s of 0.125 µg/ml.
Dalbavancin was generally at least twofold more active than vancomycin and daptomycin and fourfold more active than linezolid against MRSA, MSSA, and coagulase-negative staphylococcus isolates. Most (>50%) of the MRSA isolates were resistant to clindamycin (MICs of >8 µg/ml).
In vitro studies on dalbavancin have focused on aerobic gram-positive isolates that come from a variety of clinical sources, including thousands of European and American staphylococcal isolates (11, 13, 19). MIC90s for S. aureus and coagulase-negative isolates, whether susceptible or resistant to methicillin, were in most cases 0.06 µg/ml; somewhat lower MICs were observed for streptococci. Higher MICs were seen only with some vancomycin-resistant E. faecalis and E. faecium strains. Goldstein et al. (5) studied 238 anaerobes and 52 Corynebacterium species and noted that dalbavancin was 1 to 3 dilutions more active than vancomycin against most strains.
Recent studies (7; D. M. Citron, E. J. C. Goldstein, B. A. Lipsky, A. Tice, D. E. Morgenstern, and M. A. Abramson, 45th Intersci. Conf. Antimicrob. Agents Chemother., abstr. E-1440, 2005) have suggested that the source of isolates may be an important factor that influences the activity of agents, noting different susceptibilities of anaerobic gram-positive cocci isolated from DFIs compared to those from intra-abdominal infections. Our study is unique in that it examined only strains isolated from pretreatment DFIs. We found that dalbavancin was more active against MSSA and MRSA isolates than vancomycin, linezolid, daptomycin, and clindamycin and was active against C. perfringens, other clostridia, P. asaccharolyticus, F. magna, and A. prevotii, with MIC90s of 0.125 µg/ml.
In a recent clinical comparison, dalbavancin (>90% clinical success rate) was equivalent to linezolid in the treatment of complicated SSTIs (9) with MRSA as a baseline pathogen in 51% of patients, 23% of whom were diabetic. The bacteriology of the DFIs was not specifically elucidated. Our study showed dalbavancin to have excellent in vitro activity against the 329 gram-positive aerobic and anaerobic DFI strains tested.
The in vitro data coupled with the clinical studies suggest that dalbavancin is active against a wide variety of gram-positive isolates and might provide an advantage for patient management of DFI in emergency departments, as well as both outpatient and inpatient settings.
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ACKNOWLEDGMENTS |
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We thank Judee H. Knight and Alice E. Goldstein for various forms of assistance.
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FOOTNOTES |
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REFERENCES |
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