Research On The Factors Affecting Bacterial Culture To Diagnose Periprosthetic Joint Infection

Objective:Basic and clinical studies on some factors that may affect results of bacterial culture for diagnosing Periprosthetic Joint Infection(PJI).To analyze and evaluate whether local anesthetic lidocaine,disclosing agent methylene blue,and sonication techniques can have an impact on bacterial culture,and provide theoretical basis for improving the positive rate of bacterial culture.Methods:1.Eight isolates of reference strains of Staphylococcus aureus,Staphylococcus epidermidis,Staphylococcus hominis,Escherichia coli,Klebsiella pneumoniae,Acinetobacter baumannii,Streptococcus pyogenes,and Candida albicans were incubated on the plates.Each bacterial suspension was formed by 50-fold dilution before the test lidocaine 2%was added.For each strain,bacterial suspension was divided into 2 groups(5 samples each)exposed either lidocaine 2%or sterile non-bacteriostatic 0.45%saline.The antimicrobial property of lidocaine 2%was determined by measuring the bacterial density on agar plates incubated for 24h and comparing it with controls unexposed to lidocaine 2%.2.① Prepare the bacterial suspensions of 8 reference strains in the same manner as in Method 1.Each bacterial suspension was formed by 50-fold dilution before the test Methylene Blue(MB)solution was added.For each strain,bacterial suspension was divided into 3 groups(5 samples each)exposed either MB solution 0.1%,MB solution 0.05%or sterile non-bacteriostatic 0.45%saline.The antimicrobial property of MB solution was determined by measuring the bacterial density on agar plates incubated for 24h and comparing it with controls exposed to sterile non-bacteriostatic 0.45%saline.② Based on the modified diagnostic criteria of the Muscular Skeletal Infection Society(MSIS),a total of 17 patients with PJI who were treated with two-stage revision surgery of hip or knee in our center from October 2017 to January 2018 were included in the study.At least 3 periprosthetic tissues were taken out during surgery for bacterial culture.Each tissue was divided into two equal parts.One of the tissues was stained with 0.1%MB solution and the other was used as a control group without staining.Compare the final positive rate of culture and results of bacterial identification between the two groups.3.Based on the modified MSIS diagnostic criteria,62 patients with suspected PJI or aseptic failure admitted to our hospital from November 2016 to December 2017 were selected as study subjects,and all patients were scheduled to undergo one-stage or two-stage revision surgery.The prosthesis removed during the revision surgery is subjected to undergo sonication procedure for obtained fluid culture.According to the results of culture,the sensitivity,specificity,positive predictive value,and negative predictive value were calculated,and the difference in diagnostic efficiency between common bacterial culture and sonication fluid culture was compared.Results:1.Exposure to lidocaine 2%negatively affected microbial viability in vitro.Of the lidocaine 2%exposure,reference strains but no Streptococcus pyogenes strain resulted in fewer colony-forming units compared with the sterile saline control.The bacterial density of Staphylococcus aureus,Staphylococcus epidermidis,Klebsiella pneumoniae and Acinetobacter baumannii on agar plates were significantly inhibited by lidocaine 2%(P<0.01),as well as Candida albicans,Escherichia coli,Staphylococcus hominis(P<0.05).2.①Of the MB 0.01%or MB 0.05%exposure,reference strains but no Staphylococcus hominis and Acinetobacter baumannii strains resulted in fewer colony-forming units compared with the sterile saline control.The bacterial density of Acinetobacter baumannii on agar plates were significantly inhibited by MB solution(P<0.01),which were correlative with concentration.The colony-forming units of Staphylococcus hominis was also fewer(P<0.01),but there was no statistical difference between two concentrations of MB solution.② The positive rate of tissue culture in two groups was 82.3%and 88.2%in 17 patients,respectively,with no significant difference between them(P=0.3173>0.05).The tissue culture results in the two groups showed MB has some antimicrobial effects on Klebsiella oxytoca and Coagulase-negative Staphylococcus other than Staphylococcus haemolyticus.3.According to modified MSIS diagnostic criteria,there were 36 cases of PJI and 26 cases of aseptic failure in 62 patients.The sensitivity,specificity,positive predictive value,and negative predictive value of sonication fluid culture was 83.3%(95%CI,66.5%～93%),84.6%(95%CI,64.3%～94.9%),88.2%(95%CI,71.6%～96.2%),and 75,8%(95%CI,58.5%～90.9%),respectively.The sensitivity of sonication fluid culture was higher than that of synovial fluid culture and tissue culture,and it was significantly higher than that of the tissue culture(P<0.05).However,the specificity of sonication fluid culture was lower than that of synovial fluid culture and tissue culture,with statistically lower than that of synovial fluid culture(P<0.05).Conclusion:1.Lidocaine 2%has strong antimicrobial activities against some commonly encountered bacterial strains in PJI.As a result,infiltration anesthesia with additive-free lidocaine 2%before the arthrocentesis procedure may affect the results of synovial fluid culture.2.MB solution 0.1%has a certain antibacterial effect on some pathogenic bacteria in PJI.MB,a stain well known and readily available to orthopedic surgeons,may be potentially helpful in identifyication of biofilm on orthopedic implants and sampling of periprosthetic tissue specimens.But it may also affect the detection of some kind of bacteria.3.Sonication technique can increase the detection rate of causative microorganism in PJI,with be great value of clinical application.