COMPARISON OF RIBOTYPING, ARBITRARILY PRIMED PCR, AND PULSED-FIELD GEL-ELECTROPHORESIS FOR MOLECULAR TYPING OF LISTERIA-MONOCYTOGENES

Fifty-one clinical isolates of Listeria monocytogenes (15 isolates fro m two outbreaks and 36 epidemiologically unrelated isolates) were type d by conventional serotyping, ribotyping (RT), pulsed-field gel electr ophoresis (PFGE), and arbitrarily primed PCR (AP-PCR). Serotyping was unable to distinguish between related and unrelated strains of L. mono cytogenes. Each of the three molecular methods showed excellent typeab ility and reproducibility. Restriction with EcoRI and PvuII gave 16 an d 23 RT patterns, respectively. Restriction with ApaI or SmaI generate d 22 and 26 PFGE profiles, respectively. ApaI profiles were easier to interpret, with 10 to 15 bands each, while SmaI profiles had 15 to 20 bands each. AP-PCR with two different primers yielded 29 and 31 random ly amplified polymorphic DNA patterns, respectively. Strains from the same outbreak shared concordant patterns by each of the three methods. Of the three techniques evaluated, RT was the least discriminating an d could not distinguish between strains from the two outbreaks, The ab ilities of AP-PCR and PFGE to differentiate between strains were compa rable, However, AP-PCR was more rapid and easier to perform. We conclu de that the DNA profiles generated by either AP-PCR or PFGE can be use d to differentiate outbreak strains from epidemiologically unrelated s trains and to clearly identify unrelated strains as being distinct fro m one another. We recommend that at least two independent primers be u sed for AP-PCR typing in order to improve its discriminatory power.