Purpose: We utilized PFGE, riboprinting, and conventional sequencing to further characterize Listeria monocytogenes cantaloupe isolates and compared the identified patterns to previously reported genotypic and epidemiological data. Further, we evaluated the Phast Swab-PI-PLC-µPAD to detect cantaloupe-associated L. monocytogenes isolates.
Methods: Molecular characterizations of six cantaloupe-associated L. monocytogenes isolates were performed using PFGE (AscI and ApaI) and riboprinting (PvuII and EcoRI). Conventional sequencing was utilized to discern genetic differences in inlA, a virulence factor linked to host cell invasion. Further, a sampling and enrichment system (Phast Swab) was integrated with colorimetric paper-based analytical devices (µPAD) to sample, enrich, and detect L. monocytogenes.
Results: PFGE of the six L. monocytogenes isolates revealed five unique patterns matching those from the recent cantaloupe outbreak. These patterns were also observed, but to a lesser degree, in L. monocytogenes isolates from food and animals. Riboprinting differentiated the cantaloupe-associated isolates into four ribotypes. Two isolates shared the same PFGE pattern, but ribotyping was able to differentiate these isolates into two ribotypes, DUP_19169 and DUP_20238. Other ribotypes identified included DUP_1030 and DUP_1052 linked to human listeriosis and food/animals, respectively. Sequence analyses of inlA, further emphasized the genomic diversity of isolates. Finally, we demonstrated that the Phast Swab-PI-PLC-µPAD assay was able to detect all cantaloupe-associated L. monocytogenes isolates.
Significance: These results provide an enhanced molecular characterization of cantaloupe-associated L. monocytogenes, and subsequently link genetic differences to relevant epidemiological information. Additionally, we prove the effectiveness of a rapid assay to screen cantaloupes for L. monocytogenes contamination.