Detection and Characterization of Listeria monocytogenes in São Jorge (Portugal) Cheese Production

Listeria monocytogenes, Escherichia coli and Coagulase Positive Staphylococci in Cured Raw Milk Cheese from Alentejo Region, Portugal

Traditional cheeses are part of the Portuguese gastronomic identity, and raw milk of autochthonous species is a common primary ingredient. Here, we investigated the presence of Listeria monocytogenes, Coagulase Positive Staphylococci (CPS) and pathogenic Escherichia coli, as well as of indicator microorganisms (E. coli and other Listeria spp.) in 96 cured raw milk cheeses from the Alentejo region. Whole genome sequencing (WGS) of pathogenic E. coli and Listeria spp. as well as antimicrobial resistance (AMR) screening of E. coli isolates was also performed. L. monocytogenes, CPS > 10⁴ cfu/g and Extraintestinal E. coli were detected in 15.6%, 16.9% and 10.1% of the samples, respectively. Moreover, L. monocytogenes > 10² cfu/g and Staphylococcal enterotoxins were detected in 4.2% and 2.2% of the samples, respectively. AMR was observed in 27.3% of the E. coli isolates, six of which were multidrug resistant. WGS analysis unveiled clusters of high closely related isolates for both L. monocytogenes and L. innocua (often correlating with the cheese producer). This study can indicate poor hygiene practices during milk collection/preservation or during cheese-making procedures and handling, and highlights the need of more effective prevention and control measures and of multi-sectoral WGS data integration, in order to prevent and detect foodborne bacterial outbreaks.

Behaviour of Listeria Monocytogenes in Artisanal Raw Milk Pecorino Umbro Cheese: A Microbiological Challenge Test

In the present study, a microbiological challenge test in artificially contaminated raw milk Pecorino Umbro cheese during cheese-making was carried out. Raw ewe milk was contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes and L. monocytogenes dynamic growth were evaluated during cheese-making and storage. A significant decrease of the viable count of L. monocytogenes was observed during ripening and L. monocytogenes viable count was below the limit of quantification during storage. The results show that the product is unable to support the growth of the pathogen.

Monitoring and identification of bacteria associated with safety concerns in the manufacture of São Jorge, a Portuguese traditional cheese from raw cow's milk

The aim of this study was to assess the hygienic quality of raw milk used in the manufacture of São Jorge, a Protected Denomination of Origin Portuguese semihard cheese, as well as to ascertain the sanitary conditions prevailing during its processing. Viable counts of Enterobacteriaceae and Micrococcaceae were accordingly obtained, pertaining to 21 independent batches (including samples of raw milk, curd, and cheeses after 1, 3, and 4 months of ripening), from 7 dairy farms. Standard plate counts (log CFU per milliliter or per gram) ranged from 6.1 to 8.6 in raw milk, whereas they ranged from 7.0 to 8.0 in 4-month-old cheeses. Viable counts of Enterobacteriaceae ranged between 5.9 and 7.0 in raw milk and between 0.0 and 1.3 in 4-month-old cheeses. Species identified within this family encompassed Klebsiella oxytoca, Klebsiella cloacae, Klebsiella pneumoniae, Enterobacter sakazakii, and Escherichia coli; Klebsiella ornithinolytica, Klebsiella terrigena, and Serratia odorifera were detected only in raw milk. No Salmonella whatsoever could be detected in any of the samples. Viable counts of Micrococcaceae ranged between 4.7 and 5.9 and between 1.3 and 3.3 in raw milk and 4-month-old cheeses, respectively. Species identified within this family encompassed Staphylococcus sciuri, Staphylococcus epidermidis, Staphylococcus saprophyticus (which was found mainly in ripened cheeses), and Staphylococcus aureus (which was not detected in 4-month-old cheeses). Accompanying physicochemical analyses included determination of moisture, salt, and pH. Statistical analyses revealed a negative correlation between salt content and viable numbers of Enterobacteriaceae in cheese, whereas in the case of Micrococcaceae, a more negative correlation was found between viable numbers and moisture content than between viable numbers and pH. The results of our study indicate, in general, poor milk handling conditions in all farms, given that the indicators total mesophile and Enterobacteriaceae counts were high, between 100- and 1,000-fold those enforced by international standards pertaining to the matrices in question. However, by the time of regular consumption (i.e., after 4 months of ripening), São Jorge cheeses exhibit low levels of contamination by Enterobacteriaceae and S. aureus, as well as absence of Salmonella.