Species and antimicrobial susceptibility testing of coagulase-negative staphylococci in periprosthetic joint infections.

The objective was to evaluate the distribution of coagulase-negative staphylococci (CNS) involved in periprosthetic-joint infections (PJIs) and to describe their susceptibility profile to antibiotics. We conducted a multicentre retrospective study in France, including 215 CNS PJIs between 2011 and 2015. CNS PJIs involved knees in 54% of the cases, hips in 39%, other sites in 7%. The distribution of the 215 strains was: Staphylococcus epidermidis 129 (60%), Staphylococcus capitis 24 (11%), Staphylococcus lugdunensis 21 (10%), Staphylococcus warneri 8 (4%), Staphylococcus hominis 7 (3%), Staphylococcus haemolyticus 7 (3%). More than half of the strains (52.1%) were resistant to methicillin, 40.9% to ofloxacin, 20% to rifampicin. The species most resistant to antibiotics were S. hominis, S. haemolyticus, S. epidermidis, with 69.7% of the strains resistant to methicillin and 30% simultaneously resistant to clindamycin, cotrimoxazole, ofloxacin and rifampicin. No strain was resistant to linezolid or daptomycin. In this study on CNS involved in PJIs, resistance to methicillin is greater than 50%. S. epidermidis is the most frequent and resistant species to antibiotics. Emerging species such S. lugdunensis, S. capitis and Staphylococcus caprae exhibit profiles more sensitive to antibiotics. The antibiotics most often active in vitro are linezolid and daptomycin.

Can we rely on histopathological results for the diagnosis of prosthetic joint infection?

BACKGROUND: Histopathology is one of the diagnostic criteria for prosthetic joint infection (PJI) proposed by all academic societies. The aim of this study was to compare histopathological and microbiological results from samples taken intraoperatively at the same site in patients with suspected or proven PJI. PATIENTS AND METHODS: We conducted a monocenter retrospective study including all patients having undergone surgery from 2007 to 2015 with suspected or proven PJI. During surgery, both histopathological and microbiological samples were taken. Patients with a history of antimicrobial treatment 2 weeks prior to surgery were excluded. We considered as major criteria and gold standard for PJI diagnosis the presence of a sinus tract communication and/or the same microorganism in at least two cultures. RESULTS: Finally, 181 patients who underwent 309 surgeries were included. The median number of samples per surgery was 4 (interquartile range (IQR) = 3-5) for histopathology and 5 (IQR = 4-6) for microbiology. Major criteria were observed in 177 patients (57.3%), while positive histology in at least one intraoperative sample was present in 119 (38.5%). The concordance was 74%. The sensitivity and specificity of histopathology were 61% and 92% respectively. Available "histopathology-culture" sample pairs numbered 1247. Among them, positive histopathology was found in 292 samples (23%) and culture in 563 (45%). Concordance was 64%. The highest correlation was observed for very early infection (<1 month) (OR: 9.1, 95% CI: 3.6-23) and for virulent microorganisms, such as Staphylococcus aureus (OR: 7.8, 95% CI: 5.2-11.8), Streptococci (OR:7.8; 95% CI: 4-15.2) or Enterobacterales (OR: 7.4; 95% CI: 4.2-13.1). CONCLUSION: Histopathologic examination is a valuable criterion for PJI diagnosis, but it may lack sensitivity for chronic infections or due to low-virulence pathogens.

Characteristics of Enterobacter cloacae prosthetic joint infections.

OBJECTIVES: Enterobacter cloacae prosthetic joint infections (PJI) are rare and poorly documented. PATIENTS AND METHODS: We conducted a retrospective and monocentric study in an orthopedic unit supporting complex bone and joint infections. Between 2012 and 2016 we collected background, clinical, biological, and microbiological data from 20 patients presenting with prosthetic joint infection and positive for E. cloacae, as well as data on their surgical and medical treatment and outcome. RESULTS: Infections were localized in the hip (n=14), knee (n=5), or ankle (n=1). The median time between arthroplasty and septic revision was three years. Fourteen patients (70%) had undergone at least two surgeries due to previous prosthetic joint infections. The median time between the last surgery and the revision for E. cloacae infection was 31 days. Eleven patients (55%) were infected with ESBL-producing strains. The most frequently used antibiotics were carbapenems (n=9), cefepime (n=7), quinolones (n=7), and fosfomycin (n=4). The infection was cured in 15 patients (78.9%) after a 24-month follow-up. Five patients had a recurrent infection with another microorganism and four patients had a relapse of E. cloacae infection. The global success rate was 52.7% (58.3% for DAIR and 75% for DAIR+ciprofloxacin). CONCLUSION: Prosthetic joint infections due to E. cloacae usually occur early after the last prosthetic surgery, typically in patients with complex surgical and medical histories. The success rate seems to be increased when DAIR is associated with ciprofloxacin.