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Characterization and antimicrobial resistance of Listeria monocytogenes isolated from retail beef meat in Poland.

Four hundred seventeen retail beef meat samples purchased in the eastern part of Poland during October 2009 to January 2011 were tested for the presence of Listeria monocytogenes. It was found that 81 (19.4%) of them were positive for this microorganism as identified by the culture and polymerase chain reaction (PCR) methods. Molecular serotyping performed by PCR revealed that the majority of the isolates (50 strains; 61.7%) were of 1/2a serotype. Furthermore, 26 (32.1%) L. monocytogenes strains were classified as 1/2c serotype, and only five strains belonged to serotypes 1/2b or 4b (four and one isolates, respectively). All the isolates were positive for the inlA, inlC, inlJ, and lmo2672 sequences, whereas two L. monocytogenes (both of 4b serotype) had another virulence marker gene--llsX. The results of the antimicrobial resistance revealed that the strains were sensitive to most of the antimicrobials used in the study except oxacillin (62.7% resistant strains). Several isolates (17.3%) were also resistant to ceftriaxone. Our results indicate that L. monocytogenes identified in raw beef meat possessed virulence markers that make them potentially pathogenic for humans. Therefore, this kind of food may create a public health concern.