Abiotrophia defectiva as a Rare Causative Agent of Periprosthetic Total Knee Arthroplasty Infections: A Case Report and Literature Review

Case History

A 69-year-old female who underwent a TKA a year ago was admitted with the complaints of pain, erythema, and swelling in the operated knee. She had no relevant medical history except a tooth extraction that occurred 3 months before the operation.

A plain radiograph was normal. Additionally, laboratory findings included high-levels of C-reactive protein (38 mg/L), erythrocyte sedimentation rate at 58 mm/h, and normal white blood count (7800 cells/mL). The initial diagnosis was periprosthetic TKA infection. No bacterial growth was yielded in any of the cultivations. A two-stage revision arthroplasty was applied.

In the first stage revision, a debridement of the infected area, removal of implants, and insertion of an antibiotic-impregnated cement spacer were performed. Meanwhile, synovial fluid aspirates were sent for microbiological analysis.

Laboratory Investigations

Intraoperative synovial fluid was inoculated into aerobic (BD BACTEC Plus Aerobic/F, USA) and anaerobic (BD BACTEC Lytic/10 Anaerobic/F, USA) blood-culture bottles and incubated in automatic chambers for 14 days. The aerobic bottle produced Gram-positive cocci after a 5-day incubation at 37°C, and highly pleomorphic coccobacilli in small chains were recognized after subculturing of the aerobic bottle in chocolate agar with supplemented pyridoxal 37°C under a 5% CO2 atmosphere for 24 hours. No growth was observed in 5% sheep-blood agar. The biochemical test results for the colonies were as follows: negative catalase and oxidase tests, and no growth on media with bile-esculin and 6.5% NaCl. Furthermore, although small colonies in small chains were observed in chocolate agar plate, these colonies were not identified by conventional identification methods or rapid identification systems including API Coryne and Rapid ID 32 Strep (bioMe´rieux, France).

Therefore, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis was performed with a MicroFlex LT mass spectrometer (Bruker Daltonics, Bremen, Germany). Each colony was overlaid with 1 μL of matrix solution, and mass spectra of the sample was then transferred to the Biotyper software (version 3.0; Bruker, Karlsruhe, Germany). The analyses were performed by comparing with other spectra in the Bruker database library. A. defectiva was identified with a homology of 99.9%. Susceptibility testing was performed on Mueller–Hinton agar with pyridoxal-supplemented sheep blood (CO₂ 5%, 37°C, 24 hour), according to the guidelines of The Clinical and Laboratory Standards Institute (CLSI) for disk diffusion, and A. defectiva was detected to be susceptible to the all following antibiotics: penicillin G, erythromycin, imipenem, cefotaxime, ceftaroline, ceftriaxone, clindamycin, daptomycin, gentamicin, levofloxacin, linezolid, meropenem, penicillin, streptomycin, and vancomycin, with the exception of tetracycline. Minimal inhibitory concentrations obtained with the E-test (bioMérieux, Durham, NC, USA) were as follows: penicillin G, 0.032 mg/L; gentamicin, 4 mg/L). A combination of gentamicin and penicillin (first-line treatment) treatment was advised by the American Heart Association (AHA) guidelines for the treatment of infective endocarditis caused by Abiotrophia species⁵

After identifying the pathogen, based on drug susceptibility profile of A. defectiva, 4 × 1000.000 IU/mL penicillin G and 3 × 80 mg/L gentamicin IV had been administered parenterally for 30 days until acute phase reactants were normal and patient’s physical examination was clinically stable. Because of the increased risk for endovascular infections in patients infected with A. defectiva, endocarditis was ruled out through an echocardiography. At 12 months of follow-up, considering normal levels of acute-phase reactants, the second stage of the revision arthroplasty was applied using a hinged knee prosthesis. One year postoperatively, a labeled leukocyte scintigraphy showed no evidence of recurrence. With a satisfactory functional condition, the patient returned to her daily life without any limitations. The knee society and The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score were preop 68 and 78, respectively.

Ethical approval was not necessary for case reports in our institution, and patient consent has been obtained.