Molecular Characterization of Pseudomonas fluorescens Isolates Involved in the Italian “Blue Mozzarella” Event

Abstract

Between June and September 2010, widespread Italian consumer reports of unusual blue spoilage on fresh dairy products were publicized, resulting in the so-called blue mozzarella event. An inordinately high number of samples from mozzarella and whey cheese products of Italian and German production subsequently tested positive for Pseudomonas fluorescens. The aim of this study was to verify whether a selected P. fluorescens strain was responsible for this apparently unusual event. Molecular characterization of 181 isolated P. fluorescens strains was conducted using a newly optimized pulsed-field gel electrophoresis protocol. Although a high number of pulsotypes was found (132), only four pulsotypes were associated with more than one production plant, and only one German isolate had the same pulsotype as was detected in two Italian plants. This is the only evidence of possible cross-contamination among cheeses from the two countries. The overall results did not support the spread of contamination from German to Italian plants or the presence of one environmental strain that spread in both countries.

Pseudomonas azotoformans Belonging to Pseudomonas fluorescens Group as Causative Agent of Blue Coloration in Carcasses of Slaughterhouse Rabbits

“…As outlined above, P. fluorescens has been frequently found in food substrates, and it is well known for having been the cause of spoilage of dairy products, such as mozzarella, which exhibited a very typical blue coloration [25,26]. Unfortunately, to our knowledge, no 16S rRNA gene sequences from those strains are available in GenBank for comparison, so it has not been possible to highlight possible similarities or differences with the strains causing those events.…”

“…In fact, the chromatic alteration appeared as soon as 24 h after contamination with a suspension of 10 8 cfu/mL under the above-mentioned experimental conditions. Although P. fluorescens and P. azotoformans are rarely, if never, associated with human pathologies, there are several reports in which the presence of P. fluorescens in dairy products, fish, vegetables, and meat has led to marked deterioration of the products and withdrawal from the market [26,31,32].…”

Setup of a rapid method to distinguish among dead, alive, and viable but not cultivable cells of Pseudomonas spp. in mozzarella cheese

“…and other psychrotrophic bacteria represent the microbial spoilage contaminants of mozzarella (Baruzzi et al, 2012). The interest in the role of Pseudomonas spp., the Pseudomonas fluorescens species in particular, in spoiling of mozzarella increased in summer 2010 when the "blue mozzarella" occurred in Italy and then spread to many countries of the Europe (Nogarol et al, 2013;Andreani et al, 2014). Although several studies are available reporting the level of contamination of dairy products by the cultivable population of Pseudomonas spp.…”

Pseudomonas fluorescens in dairy products: a new case of blue mozzarella in Sardinia region

“…Nonostante il numero relativamente basso di ceppi compresi nello studio, il breve intervallo di tempo durante il quale essi sono stati isolati dimostra la presenza di ceppi diversi all'interno dello stabilimento produttivo, confermando le molteplici fonti di contaminazione. Altre indagini di caratterizzazione molecolare (Nogarol et al, 2013) ma eseguiti su un elevato numero di ceppi di P. fluorescens evidenziano come nelle aziende il numero di pulsotipi rilevanti aumenti con l'aumentare del numero di campioni analizzati. Questo consente di ipotizzare che sia possibile identificare più pulsotipi all'interno di uno stesso lotto, soprattutto in seguito ad analisi di un elevato numero di isolati da esso derivanti.…”