Presence of Listeria monocytogenes in Ready-to-Eat Artisanal Chilean Foods

Ready-to-eat (RTE) artisanal foods are very popular, but they can be contaminated by Listeria monocytogenes. The aim was to determine the presence of L. monocytogenes in artisanal RTE foods and evaluate its food safety risk. We analyzed 400 RTE artisanal food samples requiring minimal (fresh products manufactured by a primary producer) or moderate processing (culinary products for sale from the home, restaurants such as small cafés, or on the street). Listeria monocytogenes was isolated according to the ISO 11290-1:2017 standard, detected with VIDAS equipment, and identified by real-time polymerase chain reaction (PCR). A small subset (n = 8) of the strains were further characterized for evaluation. The antibiotic resistance profile was determined by the CLSI methodology, and the virulence genes hlyA, prfA, and inlA were detected by PCR. Genotyping was performed by pulsed-field gel electrophoresis (PFGE). Listeria monocytogenes was detected in 7.5% of RTE artisanal foods. On the basis of food type, positivity in minimally processed artisanal foods was 11.6%, significantly different from moderately processed foods with 6.2% positivity (p > 0.05). All the L. monocytogenes strains (n = 8) amplified the three virulence genes, while six strains exhibited premature stop codons (PMSC) in the inlA gene; two strains were resistant to ampicillin and one strain was resistant to sulfamethoxazole-trimethoprim. Seven strains were 1/2a serotype and one was a 4b strain. The sampled RTE artisanal foods did not meet the microbiological criteria for L. monocytogenes according to the Chilean Food Sanitary Regulations. The presence of virulence factors and antibiotic-resistant strains make the consumption of RTE artisanal foods a risk for the hypersensitive population that consumes them.