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

Abstract

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 <i>Listeria monocytogenes</i>, Coagulase Positive Staphylococci (CPS) and pathogenic <i>Escherichia coli</i>, as well as of indicator microorganisms (<i>E. coli</i> and other <i>Listeria</i> spp.) in 96 cured raw milk cheeses from the Alentejo region. Whole genome sequencing (WGS) of pathogenic <i>E. coli</i> and <i>Listeria</i> spp. as well as antimicrobial resistance (AMR) screening of <i>E. coli</i> isolates was also performed. <i>L. monocytogenes</i>, CPS > 10⁴ cfu/g and Extraintestinal <i>E. coli</i> were detected in 15.6%, 16.9% and 10.1% of the samples, respectively. Moreover, <i>L. monocytogenes</i> > 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 <i>E. coli</i> isolates, six of which were multidrug resistant. WGS analysis unveiled clusters of high closely related isolates for both <i>L. monocytogenes</i> and <i>L. innocua</i> (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.