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Focused ultrasound treatment of methicilin resistant Staphylococcus aureus induced abscesses: pre-clinical study
© Curiel et al; licensee BioMed Central Ltd. 2015
Published: 30 June 2015
Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that particularly threatens immunocompromised patients who are prone to develop infections that are less and less responsive to regular treatments. Moreover, MRSA can cause abscesses that are difficult to treat. Because of its capability to induce a rise of temperature at a very precise location and the known sensitivity to heat of bacteria, FUS can allow for a localized treatment for MRSA-induced abscesses.
MRSA abscesses (strain USA400) were induced after injecting a bacteria suspension at a concentration of 1.32±0.5x105 colony forming units (cfu)/mL subcutaneously in the left flank of BALB/c mice. An abscess of 6±2 mm in diameter formed after 48hrs. A small animal focused ultrasound system was then used to perform exposures on the abscess using a transducer operating at 3 MHz with a focal length of 50mm and diameter of 32mm. The focal point was positioned 2mm under the skin at the abscess center and four ultrasound exposures of 9s each were applied to each abscess under Magnetic Resonance Imaging guidance. Real-time estimation of change of temperature was done using water-proton resonance frequency (PRF) and a communication toolbox (matMRI) developed in-house. Three experimental groups of animals were tested: control, moderate temperature (52°C) and high temperature (64°C). The response to the treatment was assessed by culture and count of bacteria after treatment at two different time points: 1 and 4 days after treatment. Immune response after the treatment was evaluated by a Myeloperoxidase (MPO) assay that determined neutrophil recruitment as well as white blood cell count to evaluate the systemic inflammatory response.
Results and conclusions
Our group would like to thank the Natural Sciences and Engineering Research Council of Canada for funding this research.
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