Prevalence and characterization of Listeria monocytogenes isolated from pork meat and on inert surfaces

This study focuses on the prevalence of Listeria monocytogenes (Lm) in pork meat and on inert surfaces from slaughterhouses in Sonora, Mexico. A total of 21 Lm were obtained from 103 samples, giving a prevalence of 20.3%. The prevalence of Lm in pork loin was 15.9% and 20.8% for inert surfaces in Federal Inspection Type (FIT) slaughterhouses. For non-FIT slaughterhouses, the prevalence was 25.7%. PCR amplification of genomic DNA from the Lm isolates revealed the presence of the hlyA gene, suggesting a pathogenic nature for these isolates. The isolates obtained in this work all clustered with Lm, according to our phylogenetic analysis based on the 16S rDNA sequence. This Lm cluster indicates that Lm isolates 7-2, 4, 2-1, 10B, 8, 3, 3-3, and 9 share 16S rRNA identity with other Lm isolates that have been reported as foodborne pathogens (rR2-502, J1817, J1816, J1926) and that are involved in foodborne outbreaks. The most commonly detected serotypes were 1/2a and 1/2b. All isolates displayed differential responses to the assayed antibiotics, and most isolates were able to grow in the presence of penicillin G, or both penicillin and penicillin-derived (oxacillin) antibiotics.