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Rome, Italy

Nogarol C.,University of Bologna | Panteghini C.,IZS della Lombardia Ed Emilia Romagna | Gallina S.,University of Bologna | Daminelli P.,IZS della Lombardia Ed Emilia Romagna | And 8 more authors.
Large Animal Review | Year: 2013

Introduction - Since June 2010, an amazing high number of mozzarella cheese, produced in Italian and German plants, caused complaints in Italian consumers due to their unusual blue colour. The samples resulted positive for Pseudomonas fluorescens, psychrotrophic microorganisms, classified as ubiquitous in nature, isolated from soil, water, and vegetation. These species are particularly worrying for dairy industry as they could enter in processed dairy products through postpasteurization contamination in the milk processing plant; moreover the temperature of transport and distribution are considered permissive for the growth of these organisms. Aim - The aim of this study was the molecular characterization of P. fluorescens isolates with two different molecular techniques, in order to evaluate the genetic correlation between isolates and eventually the contamination source. Material and methods - 94 isolates of P. fluorescens, deriving from food microbiological laboratories of Italian network of Istituti Zooprofilattici Sperimentali, were collected between June 2010 and July 2011. The two molecular techniques analyze different portion of DNA: PFGE restriction endonuclease digestion was conducted on the whole genome of isolates with a rare-cutting enzymes SpeI, whereas automated riboprinting was conducted with two enzymes, EcoRI and PvuII on locus coding for rRNA operons. Results and discussion - PFGE analysis gave 44 different pulsotypes, while riboprinting with EcoRI gave 6 different ribogroups; the second restriction, operated with PvuII, gave other 7 ribogroups. All the restriction profiles were analysed with BioNumerics software, resulting in three different phylogenetic trees. Applying appropriate criteria of analysis, it was possible to evidence two different cluster of isolates, one including Italian isolates and the other including German ones. Conclusions - Our results demonstrate that the "blue-mozzarella" event was not correlated to an unusual spread of one P. fluorescens strain diffusion, underlining the high genetic variability of 94 P. fluorescens isolates, pointed out with both molecular methods.

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