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We report a case of Mycobacterium thermoresistibile as a cause of infection following total knee replacement. This infection was masked by the prior isolation of a vancomycin-resistant enterococcus. The infection was resolved with long-term therapy using moxifloxacin and doxycycline.
CASE REPORTA 73-year-old female patient who underwent a bilateral total knee replacement developed pain and swelling in the left knee and fevers 2 months after surgery. She was seen 1 week prior to admission at another facility, where material draining from the incision site was cultured. These cultures grew a vancomycin-resistant Enterococcus faecium isolate (VRE). The patient was placed on linezolid and transferred to our hospital for removal of the infected prosthetic joint.On admission the patient appeared well, with a tender left knee with a decreased range of motion and drainage from the incision site. The patient has a history of diabetes mellitus. Her laboratory values were significant only for a white blood cell count of 11.1/l, a platelet count of 619/l, an erythrocyte sedimentation rate of 90 mm/h, and a C-reactive protein level of 16.3 mg/liter. The patient was taken to the operating room for removal of the prosthetic joint. A washout of the left knee was also performed at this time. Linezolid therapy was withheld prior to surgery but restarted immediately after the procedure was performed. Tissue sections obtained perioperatively were sent for pathological examination and for bacteriological, mycological, and mycobacterial culture. Pathological examination of synovial tissue revealed chronically inflamed granulomatous tissue with fibrinous exudates, tissue necrosis, and acute inflammation. Special stains for acid-fast bacilli were negative. Gram and acid-fast stains prepared from the specimens sent for microbiological culture were negative. Routine bacteriology and mycology cultures were negative. The patient was discharged on a 6-week course of linezolid for a presumed VRE infection. After 3 weeks of incubation at 35°C, the Lowenstein-Jensen agar slant showed scant growth of a chromogenic acid-fast bacillus. This was followed by the detection of growth in the VersaTREK Myco bottle (Trek Diagnostic Systems, Cleveland, OH) a short time later. The resulting growth from the Myco bottle was identified using the Sherlock MIDI high-performance liquid chromatography system (MIDI, Newark, DE) as Mycobacterium thermoresistibile.The identification was confirmed using biochemical tests and the ability of the isolate to grow at 52°C. This isolate was positive for nitrate reduction and negative for both tellurite reduction and iron uptake.Susceptibility tests were performed utilizing Sensititre microtiter plates (Trek Diagnostic Systems) with Middlebrook 7H9 broth incubated at 42°C. For this method, a 0.5 McFarland standard suspension of the isolate is made and the manufacturer's instructions are followed depending on the panel type utilized, with 7H9 broth used in place of Mueller-Hinton broth. The resulting MICs were as follows: m...
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