Resumo

Introduction: Listeriosis is caused by Listeria monocytogenes, a foodborne pathogen, which presence is an indicative of poor hygiene conditions. Although L. monocytogenes is the most studied specie, atypical strains from other species of the genus carrying virulence genes specific to L. monocytogenes have been isolated and can represent a risk to human health. Objective: Identify virulence genes in strains of Listeria spp. originated from human infection, environment and food. Material and Methods: A total of 46 strains were studied, of which 24 were characterized, through serotyping, as L. monocytogenes, 12 L. innocua, two L. seeligeri, two de L. welshimeri and two L. ivanovii. The strains were characterized for hemolytic activity in 5% sheep blood agar and hydrolysis in ALOA medium. The detection of L. monocytogenes virulence genes (prfA, hly, plcA and inlC) was done by PCR and confirmed by sequencing. Results and Discussion: From the 46 isolates, five L. monocytogenes and two L. innocua strains, isolated from meat, showed atypical hemolytic activity and seven L. innocua isolates presented atypical halo in ALOA culture. These results confirm the risk of misidentification by phenotypic methods commonly used for microbiological diagnosis. The L. monocytogenes and L. ivanovii strains were positive for the detection of all virulence genes studied, with the exception of one weak hemolytic L. monocytogenes isolate that was negative for hly. Two of the atypical L. innocua strains were also positive to all analyzed genes and the other five were positive to hly, plcA and inlC. A L. seeligeri isolate was positive for inlC and the rest of L. seeligeri, L. innocua and L. welshimeri strains were negative to the studied genes. The detection of plcA can explain the atypical phenotype of these L. innocua strains in ALOA. The identification of hly using a primer set commonly applied for L. monocytogenes screening may explain L. innocua hemolysis and confirms that the presence of atypical Listeria isolates compromises the diagnosis and species identification usually done in microbiological laboratories. Conclusions: The results demonstrate the occurrence of potentially pathogenic Listeria environmental and food strains that can threaten human health. The detection of atypical isolates also confirms the risk of misidentification by methods commonly used for laboratorial diagnosis.