Genetic diversity of lactococci and enterococci isolated from home-made Pecorino Sardo ewes' milk cheese

Abstract

Aims: To assess the intraspeci®c genetic diversity of lactococci and enterococci isolated from 24-h, 1-and 2-month-old home-made Pecorino Sardo ewes' milk cheese. Methods and Results: Two molecular techniques, plasmid pro®ling and pulsed-®eld gel electrophoresis, were used in order to type the isolates at strain level. The present study revealed that the lactococcal and enterococcal microbial populations of home-made Pecorino Sardo cheese were complex, not only 24 h after manufacture, but also after 1 and 2 months of ripening. The genetic diversity at subspecies level ranged from 58 to 80% during the three periods examined. The study also showed that the strains that dominated in the ®rst stage of ripening were not necessarily predominant in the later periods. A high number of strains isolated at 24 h were still present in the mature cheese, but many of the genotypes were only found in the cheese after 1 or 2 months. Conclusions:The results showed a high intraspeci®c genetic diversity in the natural microbial population colonizing home-made Pecorino Sardo cheese. Two molecular techniques are necessary for a thorough and precise typing at strain level in order to better distinguish between closely related isolates and between isolates that probably belong to the same clonal lineage. Signi®cance and Impact of the Study: The genetic complexity observed in the present study is of particular relevance in the preservation of the natural micro¯ora of traditional Protected Designation of Origin raw milk cheeses, as well as in the selection of new starter strains for the dairy industry.

Quality evaluation and discrimination of semi-hard and hard cheeses from the Marche region (Central Italy) using chemometric tools

“…The occurrence of enterococci in a few raw ewes' milk cheeses was consistent with the detection of these microorganisms in other Italian raw ewes' milk cheeses produced at farmhouses (Mannu & Paba, 2002) or small-scale dairy farms (Aquilanti, Dell'Aquila, Zannini, Zocchetti, & Clementi, 2006;Aquilanti et al, 2007a). These microorganisms were also found to be part of the dominant microbiota in typical Spanish and Greek raw goats' and ewes' milk cheeses (Scintu & Piredda, 2007).…”

Sardinian goat’s milk as source of bacteriocinogenic potential protective cultures

“…Strain typing was performed by pulsed-field gel electrophoresis (PFGE) as described by Mannu and Paba (2002). In addition, scanning electron microscopy (SEM) was performed on strains with a Zeiss DSM962 microscopy (Bozzola, 2007).…”

Heat resistance of wild Lactococcus lactis strains under a thermal gradient of cooked cheese, in milk and in mini-cheeses

“…Wild lactococcal strains have been isolated from raw milk products, such as Camembert -a non-cooked cheese -or Pecorino Sardo -a semi-cooked cheese [13,29,42] -but never from cooked cheeses, although some of them were manufactured with raw milk. There is a need to select strains for new mesophilic cheese starters.…”