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Prosthetic Joint Infection Diagnosis



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Staphylococcus epidermidis Biofilm on Polycarbonate Coupons Scanning Electron Microscopy

Slide 18

January 2010

Defining the pathogen(s) is critical to directing the antimicrobial regimen. If this has not been done preoperatively, it is important that appropriate specimens for microbiologic study be collected at the time of surgery.  Antimicrobial therapy should be discontinued at least two weeks prior to collection of specimens for culture, and, at surgery, antimicrobial agents should be withheld until culture specimens have been collected.  Cultures of sinus tract exudates are often positive due to microbial skin colonization, correlate poorly with surgically obtained specimens and should be avoided.  Due to poor sensitivity, neither intraoperative swab cultures, nor periprosthetic tissue Gram stain are recommended.

Collection of multiple periprosthetic tissue specimens for aerobic and anaerobic bacterial culture is imperative because of the poor sensitivity of a single tissue culture, and to distinguish contaminants from pathogens.  It has been demonstrated that, ideally, five or six specimens should be submitted for culture.  In addition to prior systemic antimicrobial therapy, cultures may be falsely negative because of leaching of antimicrobial agents from antimicrobial impregnated cement, biofilm growth on the prosthesis surface, a low number of organisms in tissue, inappropriate culture media or inadequate culture incubation time, or prolonged transport to the laboratory.  Fungal and/or mycobacterial cultures may be considered, but are not routinely recommended.   Since microorganisms associated with Prosthetic Joint Infection attach to the prosthesis and persist as biofilm microorganisms, obtaining a sample from the prosthesis surface is useful for microbiologic diagnosis.  Vortexing combined with sonication of the implant is a simple technique that can be performed in most microbiology laboratories and has been shown to be more sensitive than and as specific as multiple periprosthetic tissue cultures for diagnosing prosthetic hip, knee and shoulder infection as well as spine implant infection, provided that an appropriate cutoff for significant results is applied.  This approach is particularly helpful in patients who have received prior antimicrobial therapy.  Sonication in bags is not recommended due to contamination.  This slide shows an outline of the procedure that we use for implant sonication.  The implant is collected in a sterilized 1-liter, straight-sided, wide-mouthed polypropylene jar and transported to the laboratory.  Four hundred milliliters of Ringer’s solution is added to the container.  The container is vortexed for 30 seconds and then subjected to bath sonication for 5 minutes, followed by an additional vortexing for 30 seconds.  In our original study we directly plated 0.5 ml of sonicate fluid to aerobic and anaerobic sheep blood agar plates, but we now concentrate the sonicate fluid hundred-fold by centrifugation and plate 0.1 ml of concentrated sonicate fluid.

Staphylococcus epidermidis Biofilm

 


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