Characterization of Listeria monocytogenes strains involved in invasive and noninvasive listeriosis outbreaks by PCR-based fingerprinting techniques

A total of 32 Listeria monocytogenes strains (16 from a recent outbreak of invasive listeriosis and 16 from two outbreaks of noninvasive listeriosis, all three occurring in Italy) were characterized by PCR-ribotyping, arbitra rily primed PCR (AP-PCR), and the recently developed infrequent-restriction -site PCR (IRS-PCR), The discriminatory ability of the techniques, first ev aluated on 29 unrelated L. monocytogenes food isolates using Simpson's inde x of diversity, was 0.714 for PCR-ribotyping, 0.690 for AP-PCR, and 0.919 f or IRS-PCR. IRS-PCR was also more capable of distinguishing among strains f rom the invasive listeriosis outbreak: three different clusters were identi fied by IRS-PCR compared to two clusters identified by both PCR-ribotyping and AP-PCR, Within each of the two outbreaks of noninvasive listeriosis, th e patterns were practically identical, as demonstrated by all three techniq ues. Only IRS-PCR succeeded in clearly discriminating the strains related t o noninvasive listeriosis from all of the other strains included in this st udy, including those from the outbreak of invasive listeriosis, This findin g may suggest the presence of unique differences in their DNA sequences.