Occurrence of foodborne pathogens in Italian soft artisanal cheeses displaying different intra- and inter-batch variability of physicochemical and microbiological parameters

Abstract

Artisanal cheeses are produced in small-scale production plants, where the lack of full automation and control of environmental and processing parameters suggests a potential risk of microbial contamination. The aim of this study was to perform a longitudinal survey in an Italian artisanal factory producing a spreadable soft cheese with no rind to evaluate the inter- and intra-batch variability of physicochemical and microbial parameters on a total of 720 environmental and cheese samples. Specifically on cheese samples, the evaluation was additionally performed on physicochemical parameters. Cheese samples were additionally collected during 15 days of storage at constant temperatures of 2 and 8°C, as well as a dynamic profile of 2°C for 5 days and 8°C for 10 days. Furthermore, Enterobacteriaceae isolates were identified at species level to have a better knowledge of the environmental and cheese microbiota potentially harboring human pathogens. High inter-batch variability was observed for lactic acid bacteria (LAB) and total bacteria count (TBC) in cheese at the end of production but not for pH and water activity. A temperature of 8°C was associated with a significantly higher load of Enterobacteriaceae in cheeses belonging to batch 6 at the end of storage, and this temperature also corresponded with the highest increase in LAB and TBC loads over cheese shelf life. Results from generalized linear mixed models (GLMMs) indicated that drains in the warm room and the packaging area were associated with higher levels of TBC and Enterobacteriaceae in cheese. Regarding foodborne pathogens, no sample was positive for verotoxigenic Escherichia coli (VTEC) or Listeria monocytogenes, whereas six Staphylococcus aureus and one Salmonella pullorum isolates were collected in cheese samples during storage and processing, respectively. Regarding Enterobacteriaceae, 166 isolates were identified at species level from all batches, with most isolates belonging to Klebsiella oxytoca and pneumoniae, Enterobacter cloacae, Hafnia alvei, and Citrobacter freundii evidencing the need to focus on standardizing the microbial quality of cow milk and on hygienic procedures for cleaning and disinfection especially in warm and maturation rooms. Further studies should be performed to investigate the potential pathogenicity and antimicrobial resistance of the identified Enterobacteriaceae species in artisanal cheeses.