Comparison Of Phenotypes And Related Genotypes Of Clinical Isolates Of Staphylococcus Epidermidis Of Prosthetic Joint Infection

Purpose :To investigate the ability of the Congo Red Agar(CRA)and microtiter plate assay(MtP)assays to detect the biofilm presence of clinical isolates of staphylococcus epidermidis from prosthetic joint infection.To investigate the relationship between the presence of biofilm and drug resistance of staphylococcus epidermidis isolates with prosthesis joint infection.To investigate the relationship between biofilm formation of staphylococcus epidermidis isolates of prosthetic joint infection with icaA,icaD and Aap gene.Methods : Specimens of patients infected after artificial joint surgery were collected from the department of joint surgery of our hospital from January 2016 to June 2018.Bacterial isolates obtained from microbial culture were used to analyze 25 strains of staphylococcus epidermidis clearly identified by time-of-flight mass spectrometry(maldi-tof-ms)with strom-assisted laser.With the help of the Congo Red Agar(CRA)test and the microtiter plate assay(MtP)test,the presence of 25 strains of staphylococcus epidermidis biofilms was detected.The CRA and MtP detection results of biofilms were analyzed using kappa consistency analysis.The 25 strains of staphylococcus epidermidis obtained by using vitek2-compact automatic bacterial identification and drug sensitivity analyzer were tested for drug sensitivity.The drug resistance rate of clinical isolated staphylococcus epidermidis was tested by chi-square test(x test).When at least one theoretical number was greater than 1 and less than 5,Fisher's exact probability method was used to test,and the result was P<0.The difference was statistically significant.The gene carrying status of staphylococcus epidermidis isolates icaA,icaD and Aap was detected by polymerase chain reaction(PCR),and the biofilm presence was detected by CRA and MtP.The paired chi-square test was used for analysis.Results: 25 strains of staphylococcus epidermidis isolates were detected by CRA test,among which 9 strains formed biofilm,accounting for 36%,and 16 strains without biofilm,accounting for 64%.25 strains of staphylococcus epidermidis isolates were detected by MtP test,among which 10 strains formed strong biofilm,accounting for40%,6 strains formed medium biofilm,accounting for 24%,1 strain formed weak biofilm,accounting for 4%,and 8 strains formed no biofilm,accounting for 32%.The presence of strong biofilm in the quantitative detection of biofilm in MtP test was defined as positive biotest,while the presence of medium,weak biofilm and no biofilm was defined as negative biofilm test.Consistency analysis was performed,and Kappa value =0.915(x>0.75),showing good consistency.Among the 25 strains of Staphylococcus epidermidis(MRSE),23 strains(92%)were resistant to methicillin-resistant Staphylococcus epidermidis(MRSE),which were not resistant to tetrandrine and vancomycin.The differences of drug resistance of rifampicin and ciprofloxacin between the strains with and without biofilm formation were statistically significant(2=8.36/6.25,p = 0.01 and 0.03,respectively).25 strains of staphylococcus epidermidis isolates were detected by PCR.9 strains carried icaA gene,10 strains carried icaD gene and 16 strains carried Aap gene.8 strains of icaA,icaD and Aap genes were expressed together,7 strains of icaA and icaD were not expressed while Aap genes were expressed,and 2 strains of icaA,icaD and Aap genes were not expressed.Combined with the presence of biofilm,8 strains of icaA,icaD and Aap genes expressed together formed biofilm by MtP and CRA detection.MtP of 7 strains only carried by Aap gene only formed medium or weak biofilm,while CRA test showed no biofilm formation.Two strains of caA,icaD and Aap genes were not expressed,and 1strain formed biofilm after MtP and CRA detection,while 1 strain did not form biofilm.Comparing ica gene positive test data with biofilm presence results,the sensitivity of CRA test for biofilm detection was 72.7%,and the specificity was 92.9%,while the sensitivity of MtP test for biofilm detection was 81.8%,and the specificity was 92.9%.Conclusion : The microtitration plate(MTP)test and Congo red AGAR(CRA)test showed good consistency in the detection of biofilm presence,but the sensitivity ofMTP in screening biofilm positive strains was better than that of CRA.Staphylococcus epidermidis isolated from clinical PJI patients in our hospital was mainly MRSE,and did not develop resistance to tegacycline and vancomycin.Among them,the biofilm-positive strains showed more resistance to rifampicin and ciprofloxacin.In order to avoid the emergence of new drug resistance spectrum,more attention should be paid to and rational use of clinical empirical antibiotic treatment.Staphylococcus epidermidis,which expressed icaA and icaD genes together,had strong biofilm formation ability.Aap gene was involved in biofilm formation,but only weak or moderate biofilm was formed when expressed alone.