Introduction Listeria monocytogenes represents a concern in the production of Gorgonzola PDO cheese. Subtyping of isolates retrieved from production environments and raw materials may lead to a better understanding of the reservoirs and contamination pathways. Objective The aim of this study was to investigate the subtypes of L. monocytogenes in the Gorgonzola production chain to identify possible reservoirs and dissemination routes Materials and Methods One producer and its conferring farms (N=20) were selected and L. monocytogenes was isolated from 12% of the collected samples (N=200) – data presented at IAFP symposium, 2010 P1-10. All Listeria strains isolated were typed through ERIC and REP PCRs. For each samples, if possible 5 colonies were selected for typing, for a total of 81 isolates. PCR profiles (combining the Two PCRs) were analysed using Dice coefficient and UPGMA algorithm in Bionumerics software. Results The analyses allowed the differentiation of L. monocytogenes and L. innocua in 9 and 7 PCR profiles (P), respectively. The former showed an overall similarity value of 75.4% and the latter of 81.2%. P1 (N=3) of L. monocytogenes was present in multiple sources (ripening surfaces and salting equipment) and P2 (N=6) in different sampling rounds (January and June 2009). P1 (N=25) and P2 (N=15) of L. innocua were found in multiple sources (performing equipment, ripening surfaces, salting equipment, moving carts) and in multiple sample rounds (P1: May 2008, January and June 2009; P2: June and October 2009). Conclusions The presence of a few highly similar strains of L. monocytogenes in the production chain, as suggested by the profiles retrieved from different sources/sampling rounds, indicates the presence of persistent and niche-adapted strains. However, no profile was shared between raw milk and environmental samples, suggesting that the plant environment, not the incoming raw milk, is the source of strains contaminating Gorganzola cheese. Acknowledgments Founds granted by Regione Piemonte – Direzione sviluppo Agricoltura – 2007.
Subtyping of Listeria monocytogenes Isolates Retrieved along the Gorgonzola PDO Production Chain
NUCERA, Daniele Michele;MORRA, Patrizia;GRASSI, Maria Ausilia
2011-01-01
Abstract
Introduction Listeria monocytogenes represents a concern in the production of Gorgonzola PDO cheese. Subtyping of isolates retrieved from production environments and raw materials may lead to a better understanding of the reservoirs and contamination pathways. Objective The aim of this study was to investigate the subtypes of L. monocytogenes in the Gorgonzola production chain to identify possible reservoirs and dissemination routes Materials and Methods One producer and its conferring farms (N=20) were selected and L. monocytogenes was isolated from 12% of the collected samples (N=200) – data presented at IAFP symposium, 2010 P1-10. All Listeria strains isolated were typed through ERIC and REP PCRs. For each samples, if possible 5 colonies were selected for typing, for a total of 81 isolates. PCR profiles (combining the Two PCRs) were analysed using Dice coefficient and UPGMA algorithm in Bionumerics software. Results The analyses allowed the differentiation of L. monocytogenes and L. innocua in 9 and 7 PCR profiles (P), respectively. The former showed an overall similarity value of 75.4% and the latter of 81.2%. P1 (N=3) of L. monocytogenes was present in multiple sources (ripening surfaces and salting equipment) and P2 (N=6) in different sampling rounds (January and June 2009). P1 (N=25) and P2 (N=15) of L. innocua were found in multiple sources (performing equipment, ripening surfaces, salting equipment, moving carts) and in multiple sample rounds (P1: May 2008, January and June 2009; P2: June and October 2009). Conclusions The presence of a few highly similar strains of L. monocytogenes in the production chain, as suggested by the profiles retrieved from different sources/sampling rounds, indicates the presence of persistent and niche-adapted strains. However, no profile was shared between raw milk and environmental samples, suggesting that the plant environment, not the incoming raw milk, is the source of strains contaminating Gorganzola cheese. Acknowledgments Founds granted by Regione Piemonte – Direzione sviluppo Agricoltura – 2007.
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