Predominance and Persistence of a Single Clone of Listeria ivanovii in a Manchego Cheese Factory Over 6 Months

In an attempt to study the diversity and persistence of molecular subtypes of pathogenic Listeria spp. in a cheese factory at the La Mancha region of Spain, 43 samples were taken from incoming raw milk (cow’s, ewe’s, goat’s and mixed species) and from certain food‐contact and environmental surfaces before and/or after sanitation. Of these samples, 12 contained pathogenic Listeria. From the chromogenic agar plates corresponding to those, 46 phosphatidylinositol‐specific phospholipase C‐positive isolates were randomly taken for further analysis, including biochemical tests and pulsed‐field gel electrophoresis (PFGE). They coincided in identifying all the 46 as Listeria ivanovii subsp. ivanovii, apparently a single PFGE type. Both ewe’s and goat’s raw milk batches from asymptomatic animals tested along the 6‐month period persistently carried the same strain, which was also obtained from inner surfaces of raw milk truck tanks and the milk dump tank at the cheese factory. Biofilm‐forming abilities of this L. ivanovii clone and interference against L. monocytogenes Scott A reference strain were tested, but failed to account for the clone’s apparent pervasive presence.