Abstract
Staphylococcus aureus infection of bone is challenging to treat because it colonizes the osteocyte lacuno-canalicular network (OLCN) of cortical bone. To elucidate factors involved in OLCN invasion and identify novel drug targets, we completed a hypothesis-driven screen of 24 S. aureus transposon insertion mutant strains for their ability to propagate through 0.5 μm-sized pores in the Microfluidic Silicon Membrane Canalicular Arrays (μSiM-CA), developed to model S. aureus invasion of the OLCN. This screen identified the uncanonical S. aureus transpeptidase, penicillin binding protein 4 (PBP4), as a necessary gene for S. aureus deformation and propagation through nanopores. In vivo studies revealed that Δpbp4 infected tibiae treated with vancomycin showed a significant 12-fold reduction in bacterial load compared to WT infected tibiae treated with vancomycin (p<0.05). Additionally, Δpbp4 infected tibiae displayed a remarkable decrease in pathogenic bone-loss at the implant site with and without vancomycin therapy. Most importantly, Δpbp4 S. aureus failed to invade and colonize the OLCN despite high bacterial loads on the implant and in adjacent tissues. Together, these results demonstrate that PBP4 is required for S. aureus colonization of the OLCN and suggest that inhibitors may be synergistic with standard of care antibiotics ineffective against bacteria within the OLCN.
Highlights
Osteomyelitis is a devastating disease caused by bacterial infection of the bone, for which treatment guidelines are suboptimal [1,2] and oftentimes require surgical intervention in addition to extended antimicrobial therapy [3]
penicillin binding protein 4 (PBP4) is Critical for S. aureus Invasion of osteocyte lacuno-canalicular network (OLCN) in Bone and analysis, decision to publish, or preparation of the manuscript
Expert consensus has challenged the use of antibiotic-loaded bone cement (ALBC), which is a standard of care treatment for S. aureus osteomyelitis, despite the substantial lack of evidence to demonstrate clinical efficacy of ALBC [11]
Summary
Osteomyelitis is a devastating disease caused by bacterial infection of the bone, for which treatment guidelines are suboptimal [1,2] and oftentimes require surgical intervention in addition to extended antimicrobial therapy [3]. Staphylococcus aureus is the most common pathogen isolated from chronic osteomyelitis [4], with 50% of prosthetic joint infections caused by hardto-treat methicillin resistant S. aureus (MRSA) [2,5]. Expert consensus has challenged the use of antibiotic-loaded bone cement (ALBC), which is a standard of care treatment for S. aureus osteomyelitis, despite the substantial lack of evidence to demonstrate clinical efficacy of ALBC [11]. These experts highlighted the great need to develop novel antibiotics that target S. aureus infection of bone, which is considered very challenging to treat [11]
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