Listeria in ready-to-eat and unprocessed foods produced in Portugal

Abstract

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 ewe's, cow's or goat's 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.