Frequency of isolation of listeria species in different retail foods in Colombia

Listeria monocytogenes was recognizing as a causal agent of human and animal listeriosis more than 70 years ago. However, L. ivanovii have not been frequently associated with the human illness, being a recognized animal pathogen. In both cases, the infections occur through contaminated food consumption. The main objective of this work was to determine the frequency of isolation of Listeria sp in different common foodstuffs at distinct states of Colombia, from August 2002 to August 2005. One thousand four hundred eighty one (1481), food samples (cattle meat, poultry carcass, poultry meat, goat milk, cow milk and several types of cheeses) were assayed. For genus identification, conventional culture methods and presumptive tests were use. Multiple-PCR employing L1-U1/LF-LR primers allowed distinguishing between L. monocytogenes and the other species. Species were discriminated by biochemical tests and sugar fermentation assays. Listeria spp, was detected in 16% of samples. The general frequency by states was 2.2, 13, 26 and 0% for L. monocytogenes, while the frequency of L. innocua was 1.6, 0.4, 0 and 2.4%, both in Norte de Santander, Cundinamarca, Boyacá and Córdoba respectively. L. ivanovii was isolated in 15% of the samples from Córdoba. The 9.4% of L. ivanovii isolations were resistant to antibiotics, suggesting the possible transfer of resistance genes. Listeria spp., circulates in food products of these regions of the country, and in spite of the still discrete sample analyzed in this study, it represents a risk for the animal and public health as well as trade of foods products of animal origin.