Abstract: Objective To study the possibility of direct detection and identification of mycobacteria by PCR in skin specimens.Methods The comparison of PCR with in vitro culture of M.smegmatis was conducted at three levels.First,serial dilutions of M.smegmatis DNA was amplified with primers aiming at hsp65 gene to testify the sensitivity of PCR for mycobacterial detection,and the same dilutions of suspension of M.smegmatis was inoculated in Löwenstein-Jensen medium to assessed the sensitivity of in vitro culture.Secondly,the results of detecting simulant clinical specimens by PCR with or without pretreatment were compared with those by in vitro culture.Thirdly,the results of detecting 37 clinical skin specimens suspected to be infected with mycobacteria by PCR with or without pretreatment were compared with those by in vitro culture.Results The sensitivity of both PCR and in vitro culture for detection of serial dilutions of bacterial suspension of M.smegmatis was 1×10² cells/mL.The detection rates of PCR for simulant clinical skin specimen at 1×10² cells/mL with and without pretreatment were 60% and 0 respectively,and the detection rates of in vitro culture were 80% and 100%,respectively.The detection rate of PCR was 100% for simulant clinical skin specimens at 1×10³ cells/mL.From the 37 clinical skin specimens,7 and 2 positive cases were detected by PCR with and without pretreatment respectively,however,9 positive cases were detected by in vitro culture.Conclusion With the pretreatment of clinical skin specimens,the sensitivity of PCR approximates 80% and the time needed for detection is obviously shortened.

Key words: Mycobacterium, Polymerase chain reaction