R. M. Alden Research Laboratory, Santa Monica, California 90404, 1 and David Geffen School of Medicine at UCLA, Los Angeles, California

Transcription

1 ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Aug. 2006, p Vol. 50, No /06/$ doi: /aac Copyright 2006, American Society for Microbiology. All Rights Reserved. In Vitro Activities of Dalbavancin and 12 Other Agents against 329 Aerobic and Anaerobic Gram-Positive Isolates Recovered from Diabetic Foot Infections Ellie J. C. Goldstein, 1,2 * Diane M. Citron, 1 Yumi A. Warren, 1 Kerin L. Tyrrell, 1 C. Vreni Merriam, 1 and Helen T. Fernandez 1 R. M. Alden Research Laboratory, Santa Monica, California 90404, 1 and David Geffen School of Medicine at UCLA, Los Angeles, California Received 6 March 2006/Returned for modification 5 April 2006/Accepted 3 May 2006 Tests of dalbavancin s in vitro activity against 209 aerobic and 120 anaerobic isolates from pretreatment diabetic foot infections showed an MIC 90 of <0.125 g/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 MIC 90 s for MSSA and MRSA of 0.5 and 1 g/ml for vancomycin, 4 and 4 g/ml for linezolid, 0.5 and 0.5 g/ml for daptomycin, and 0.25 and >8 g/ml for clindamycin. Diabetes will affect 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 K 1, 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). * Corresponding author. Mailing address: Alden Research Laboratory, 2021 Santa Monica Blvd., no. 740 East, Santa Monica, CA Phone: (310) Fax: (310) ejcgmd@aol.com. 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). The MICs for anaerobes were determined by the agar dilution method using brucella agar supplemented with hemin, vitamin K 1, and 5% laked sheep blood. Antimicrobial agents were reconstituted according to the manufacturers instructions. Serial twofold dilutions of dalbavancin were prepared at 100-fold the final concentration in dimethyl sulfoxide on the day of the test and added to the agar medium at a dilution of 1:100. The other antimicrobial agents were diluted and added according to the CLSI procedure (17). The agar plates were inoculated with a Steers replicator (Craft Machine Inc., Chester, PA) with an inoculum of 10 5 CFU/spot, incubated in an anaerobic chamber (Anaerobe Systems) at 37 C for 44 to 48 h, and then examined. Control strains (Bacteroides fragilis ATCC 25285, the newly proposed Clostridium difficile ATCC 70057, and S. aureus ATCC 29213) were tested simultaneously. 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 dryformat 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 Ca 2 to 50 mg/liter. The trays were stored at 70 C until used. Enterococcus faecalis ATCC and S. aureus ATCC were tested simultaneously. The in vitro activities of dalbavancin and 12 comparator agents are shown in Table 1. Dalbavancin had an MIC 90 of g/ml against methicillin-susceptible S. aureus (MSSA) and MRSA isolates. Other MIC 90 s for MSSA and MRSA, respectively, were 0.5 and 1 g/ml for vancomycin, 4 and 4 g/ml for linezolid, 0.5 and 0.5 g/ml for daptomycin, and 2875

2 2876 NOTES ANTIMICROB. AGENTS CHEMOTHER. TABLE 1. In vitro activities of dalbavancin and 12 comparator antimicrobial agents against 209 aerobic and 120 anaerobic gram-positive organisms Aerobes MSSA (43) Dalbavancin Vancomycin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Oxacillin MRSA (60) Dalbavancin Vancomycin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Oxacillin Staphylococcus spp., coagulase-negative (20) a Dalbavancin Vancomycin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Oxacillin Streptococcus agalactiae (24) Dalbavancin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Beta-hemolytic Streptococcus spp., other (22) b Dalbavancin Vancomycin Linezolid Daptomycin Continued on following page

3 VOL. 50, 2006 NOTES 2877 TABLE 1 Continued Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Corynebacterium amycolatum (20) Dalbavancin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Corynebacterium spp. (20) c Dalbavancin Linezolid Daptomycin Meropenem Imipenem Piperacillin-tazobactam Penicillin Amoxicillin-clavulanate Levofloxacin Clindamycin Cefotetan Anaerobes Clostridium spp. (20) d Dalbavancin Vancomycin Daptomycin Linezolid Imipenem Meropenem Amoxicillin-clavulanate Penicillin Piperacillin-tazobactam Cefotetan Levofloxacin Clindamycin Metronidazole Peptoniphilus asaccharolyticus (20) Dalbavancin Vancomycin Daptomycin Imipenem Meropenem Amoxicillin-clavulanate Penicillin Piperacillin-tazobactam Cefotetan Levofloxacin Continued on following page

4 2878 NOTES ANTIMICROB. AGENTS CHEMOTHER. TABLE 1 Continued Clindamycin Metronidazole Finegoldia magna (29) Dalbavancin Vancomycin Daptomycin Linezolid Imipenem Meropenem Amoxicillin-clavulanate Penicillin Piperacillin-tazobactam Cefotetan Levofloxacin Clindamycin Metronidazole Anaerococcus prevotii (20) Dalbavancin Vancomycin Daptomycin Imipenem Meropenem Amoxicillin-clavulanate Penicillin Piperacillin-tazobactam Cefotetan Levofloxacin Clindamycin Metronidazole Other anaerobic gram-positive cocci (31) e Dalbavancin Vancomycin Daptomycin Imipenem Meropenem Amoxicillin-clavulanate Penicillin Piperacillin-tazobactam Cefotetan Levofloxacin Clindamycin Metronidazole a Staphylococcus epidermidis (4), S. haemolyticus (3), S. capitis (1), S. caprae (1), S. cohnii (1), S. hominis (1), S. lugdunensis (3), S. schleiferi (1), S. sciuri (2), S. simulans (2), and S. warneri (1). b Streptococcus group G (19) and S. pyogenes (3). c Corynebacterium group F-1 (1), C. glucuronolyticum (1), C. jeikeium (10), C. simulans (1), C. striatum (5), C. urealyticum (1), and Corynebacterium sp. (1). d Clostridium cadaveris (4), C. clostridioforme (3), C. innocuum (1), C. perfringens (10), C. sphenoides (1), and C. subterminale (1). e Peptostreptococcus anaerobius (9), Peptoniphilus harei (4), P. vaginalis (7), Micromonas micros (7), and Anaerococcus tetradius (4) and 8 g/ml for clindamycin. The MIC of dalbavancin for one of three strains of Staphylococcus haemolyticus was 2 g/ml. To determine if this was peculiar to the species, we tested 16 additional strains and found the range to be 0.06 to g/ml. Against Streptococcus agalactiae, Streptococcus pyogenes, and group G beta-hemolytic streptococci, dalbavancin had an MIC 90 of g/ml. Dalbavancin inhibited Corynebacterium amycolatum and Corynebacterium jeikeium strains at 1 g/ml and was active against 120 anaerobes (Clostridium perfringens, other clostridia, Peptoniphilus asaccharolyticus, Finegoldia magna, Anaerococcus prevotii, and other anaerobic gram-positive cocci), with MIC 90 sof g/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 g/ml). In vitro studies on dalbavancin have focused on aerobic gram-positive isolates that come from a variety of clinical

5 VOL. 50, 2006 NOTES 2879 sources, including thousands of European and American staphylococcal isolates (11, 13, 19). MIC 90 s for S. aureus and coagulase-negative isolates, whether susceptible or resistant to methicillin, were in most cases 0.06 g/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 MIC 90 sof g/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. This study was sponsored in part by a grant from Vicuron Pharmaceuticals Inc. We thank Judee H. Knight and Alice E. Goldstein for various forms of assistance. REFERENCES 1. Bailey, T. S., H. M. Yu, and E. J. Rayfield Patterns of foot examination in a diabetes clinic. Am. J. Med. 78: Diederen, B. M., and J. A. Kluytmans The emergence of infections with community-associated methicillin resistant Staphylococcus aureus. J.Infect. 52: Frazee, B. W., J. Lynn, E. D. Charlebois, L. Lambert, D. Lowery, and F. 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