Antimicrobial Activity of Dalbavancin and Comparator Agents Tested against Gram-Positive Clinical Isolates Causing Bone and Joint Infections in United States (US) Medical Centers (2011–2016)

BACKGROUND: Bone and joint infections (BJI) comprise a series of disorders, including septic arthritis, osteomyelitis, and prosthetic joint infections. We evaluated the activity of dalbavancin (DALBA) against pathogens isolated from BJI in US hospitals. METHODS: A total of 744 organisms collected from 55 hospitals in 2011–2016 were evaluated, including 463 S. aureus, 88 coagulase-negative staphylococci (CoNS), 104 β-haemolytic streptococci (BHS), 60 E. faecalis, and 29 viridans group streptococci (VGS). Bacteria were identified by standard algorithms and MALDI-TOF-MS. Susceptibility testing was performed by CLSI methods (M07-A10); interpretation of MIC results used CLSI (2017) and EUCAST (2017) criteria. RESULTS: S. aureus (62.2%) was the most common pathogen associated with BJI, followed by BHS (14.0%) and CoNS (11.8%). All S. aureus (41.5% methicillin-resistant [MRSA]) isolates were susceptible (S) to DALBA, linezolid (LNZ), teicoplanin (TEI) and vancomycin (VAN), while daptomycin (DAPTO) and clindamycin (CLI) showed susceptibility rates of 99.8% and 87.7% (CLSI), respectively. DALBA MIC results (MIC(50/90), ≤0.03/0.06 μg/mL) were ≥8-fold lower compared with DAPTO (MIC(50/90), 0.25/0.5 μg/mL) against all S. aureus. Among CoNS, (61.4% MRSA), DALBA (MIC(50/90), ≤0.03/0.06 μg/mL) was the most potent agent, followed by DAPTO (MIC(50/90), 0.25/0.5 μg/mL), LNZ (MIC(50/90), 0.5/1 μg/mL), and VAN (MIC(50/90), 1/2 μg/mL). DALBA inhibited all E. faecalis isolates at ≤0.25 μg/mL (FDA S breakpoint), except for 3 VAN-resistant (VanA) isolates. High susceptibility rates for ampicillin (98.3%; CLSI), DAPTO (100.0%), LNZ (100.0%), TEI (93.3%) and VAN (93.3%) were obtained against E. faecalis. DALBA, DAPTO, LNZ, ceftriaxone, penicillin, and VAN were active against all BHS (100.0%S), while DALBA (MIC(50/90), ≤0.03/0.06 μg/mL; 100.0%S) was the most active agent against VGS, inhibiting all isolates at ≤0.06 μg/mL. Ceftriaxone, LNZ, DAPTO, and VAN were also active against VGS (93.1 – 100.0%S; CLSI), whereas CLI (82.8%S) had marginal activity. CONCLUSION: DALBA demonstrated potent in vitro activity against common gram-positive isolates causing BJI (2011–2016) and appears to be a viable candidate for treating BJI/osteomyelitis caused by gram-positive cocci. DISCLOSURES: H. S. Sader, Allergan: Research Contractor, Research grant; R. E. Mendes, Allergan: Research Contractor, Research grant; R. K. Flamm, Allergan: Research Contractor, Research grant; M. A. Pfaller, Allergan: Research Contractor, Research grant