Occurrence of Listeria spp. and Listeria monocytogenes Isolated from PDO Taleggio Production Plants.

Erica Tirloni,Francesco Pomilio,Marina Torresi,Simone Stella,Enrico P L De Santis,Christian Scarano,Cristian Bernardi

doi:10.3390/foods9111636

Abstract

The present study evaluated the presence of Listeria spp. and L. monocytogenes in four plants producing PDO Taleggio cheese. A total of 360 environmental samples were collected from different areas during production. The sampling points were identified as Food Contact Surfaces (FCS), transfer-Non Food Contact Surfaces (tr-NFCS), and non-transfer-NFCS (non-tr-NFCS). Fifty-nine ingredients/products were also analyzed. Listeria spp. was found in all the plants with a mean prevalence of 23.1%; plants that included a ripening area showed significantly higher prevalence if compared to the other plants. The positivity rate detected on FCS was moderate (~12%), but significantly lower if compared to NFCS (about 1/4 of the samples, p < 0.01). Among the FCS, higher prevalence was revealed on ripening equipment. Listeria spp. was never detected in the ingredients or products. A total of 125 Listeria spp. isolates were identified, mostly as L. innocua (almost 80%). L. monocytogenes was detected only from two FCS samples, in an area dedicated to the cutting of ripened blue cheeses; strain characterization by whole genome sequencing (WGS) evidenced a low virulence of the isolates. The results of the present study stress the importance of Listeria spp. management in the dairy plants producing PDO Taleggio and similar cheeses, mainly by the application of strict hygienic practices.

Highlights

Listeria monocytogenes remains a food safety challenge for cheese production plants: dairy products contaminated by this pathogen have been associated to some strong-evidence listeriosis outbreaks that occurred in Europe in the last decade [1,2]
The results obtained from the detection of Listeria spp. and L. monocytogenes in the samples are summarized in Tables 1 and 2
The results of the present study show the diffusion of Listeria spp. in different PDO Taleggio producing plants, with very low prevalence of L. monocytogenes

Summary

Introduction

Listeria monocytogenes remains a food safety challenge for cheese production plants: dairy products contaminated by this pathogen have been associated to some strong-evidence listeriosis outbreaks that occurred in Europe in the last decade [1,2]. Little et al [3] stated that 2% of dairy products produced from raw or thermized milk were characterized by L. monocytogenes counts above the limits reported by EU Regulation 2073/2005 [4]; in addition, dairy products produced from pasteurized milk should be considered as potential sources of outbreaks, as reported by previous authors [5,6]. Many sources are involved: raw milk can be contaminated at farm level and lead the contamination in the cheese-processing environment [10]; this event could have a negative impact mainly on the production of dairy products from raw or unpasteurized milk. Previous studies reported prevalence up to 52% in dairy plants [12,13,14,15]

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Conclusion