Disappearance of rifampin resistance in MRSA foreign body osteomyelitis

Project: Research project

Description

Project SummaryDue to an aging population and advances in medical technology, prosthetic joint placement is increasing infrequency. Prosthetic joint infection (PJI) affects up to 2% of prosthetic joints. Staphylococci are the mostcommon causes of PJI, with Staphylococcus aureus being the most common pathogen overall andStaphylococcus epidermidis being the second most common staphylococcal species involved. Treatment ofPJI is problematic due to the limited activity of most antimicrobial agents against microbial biofilms. Rifampin,however, has anti-biofilm activity, and is a cornerstone drug in the management of staphylococcal PJI, whenmanaged with débridement and implant retention (DAIR). Unfortunately, resistance to rifampin, mediated bysingle base pair mutations in the target gene, is readily selected and would be expected to compromisemanagement of staphylococcal PJI using a DAIR strategy. Our preliminary data surprisingly suggest, however,that selected rifampin resistance may not necessarily negatively impact future treatment using rifampin-basedtherapy. Specifically, we have shown that, as expected, rifampin resistance is selected following rifampinmonotherapy in a rat model of methicillin-resistant S. aureus foreign body osteomyelitis (FBO). But,surprisingly, rifampin resistance ?disappears? two weeks following cessation of treatment, with only rifampinsusceptible S. aureus being detectable. We have shown that rifampin resistance does not confer decreasedfitness when bacteria are grown alone in vitro or in vivo; however, rifampin-resistant bacteria are out-competedby rifampin-susceptible bacteria when grown together in vitro and in vivo. And, when treating FBO with tworounds of rifampin monotherapy, resistance is observed at a lower frequency following the second than the firstround of rifampin exposure. These observations suggest that rifampin may be a usable agent in biofilm-associated infections in which rifampin resistance has been previously selected.The central hypothesis of our proposed studies is therefore that in experimental FBO, treatment with rifampincan be successful even if rifampin resistance has been previously selected. Our objectives are to develop anexperimental FBO model that allows sampling of bacteria in real time from the same animal and to use themodel to define the kinetics of selection and disappearance of rifampin resistance. Whereas in traditionalosteomyelitis models, microorganisms are analyzed at single time-points (i.e., when animals are sacrificed),the proposed model will allow analysis of bacteria from the same animal over time. We will perform wholegenome sequencing on bacteria recovered at multiple time-points during and following one and two rounds ofrifampin treatment. This will allow definition of rifampin resistance- and fitness-associated mutations thatemerge during and following initial rifampin treatment, and subsequent re-exposure to rifampin. This approachwill pinpoint mutations that may occur in rifampin-susceptible bacteria allowing their persistence or conferringupon them a selective advantage over their rifampin-resistant counterparts, even when challenged withrifampin. Finally, we will compare outcomes of FBO treated with either rifampin monotherapy followed byrifampin combination therapy or rifampin combination therapy alone. This will allow us to determine whetherrifampin-containing regimens may be an option in the treatment of PJI in which rifampin resistance has beenpreviously selected. Results of the proposed studies will define the kinetics of in vivo selection of rifampinresistance and identify mutations that play a role in out-competition of rifampin-resistant bacteria by those thatare rifampin-susceptible. Additionally, our studies will inform clinical treatment options in the scenario ofselected rifampin resistance and lay the groundwork for future experiments defining optimal therapy followingselection of rifampin resistance.
StatusFinished
Effective start/end date6/1/16 → 5/31/18

Funding

  • National Institutes of Health: $198,750.00

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Osteomyelitis
Rifampin
Methicillin-Resistant Staphylococcus aureus
Foreign Bodies
Joints
Bacteria
Biofilms
Infection
Mutation
Therapeutics
Staphylococcus aureus