Listeria in ready-to-eat and unprocessed foods produced in Portugal Original Research Article

Between October 1998 and April 2000, 429 food samples were investigated for the presence ofListeria spp. The foodstuffs included 138 ready-to-eat foods (68 traditional hard and semi-hard Portuguese cheeses, 23 salad vegetables and 47 cooked and/or cured meats) and 291 uncooked foods (14 raw vegetables, 65 raw chicken and 212 raw eweʹs, cowʹs or goatʹs milk). Listeria spp. were recovered from 63 samples (15%). Listeria monocytogenes was present in 39 (9%) samples, Listeria innocua in 12 (3%), Listeria seeligeri in 23 (5%), Listeria ivanovii in seven (2%) and Listeria grayi in two (0·5%). More than one Listeria species was recovered from 18 samples. A combination of serotyping, phage-typing, cadmium and arsenic sensitivities were used to subtype 36 of the L. monocytogenes isolates: at least nine different strains were recognized. Four food samples yielded two different L. monocytogenes strains.