SUMMARY
Characterization of Listeria monocytogenes isolates obtained from raw cheese samples acquired from different Costa Rican producer zones
In Costa Rica, almost 25% of the national milk production is used for the elaboration of non pasteurized soft cheese, and the annual intake of this product is around 4-5 kg per capita. This product has been identified as the source of food borne outbreaks due to Listeria monocytogenes. Given that, the isolation and identification of this bacterium from non pasteurized soft cheese samples coming from two producer zones of Costa Rica was performed. 110 cheese samples were collected, from which 27 L. monocytogenes strains were isolated. These were characterized using biochemical and serological tests, also, susceptibility to common used antibiotics, test tube hemolysis and invasion in Hela cells trials were performed. 85% of the strains evaluated were sensible to all the antibiotics analyzed, nevertheless, four strains presented resistance to different agents, including streptomycin, kanamycin, cephalotin and tetracycline. Also, multiple resistance patterns were found. 88,9% of the studied isolates were positive for the test tube hemolysis trial; 22,2% presented invasion percentages higher than the clinical origin strain used as control. It is important to point out that all the invasive strains were completely susceptible to the antibiotics tested. The results found demonstrate the presence of L. monocytogenes in Costa Rican soft cheese samples. Also, demonstrate its high percent of susceptibility to common use antibiotics. Same time, invasion trials show that soft cheese may be a source of invasive and potentially pathogenic strains for human being.

Key words: Listeria monocytogenes, cheese, invasion, antibiotics resistance.



Recibido: 08/10/2008
Aceptado: 27/02/2009

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