The objective of this study was to investigate the molecular characterization of Listeria species isolated from frozen raw fish. A total of 219 samples consisting of 104 mackerel, 52 horse mackerel, 51 catfish and 12 herring were collected and analyzed by bacteriological, serological, antimicrobial and molecular methods.Overall, 29(56.9%) and 1(0.96%) of catfish samples and mackerel samples respectively were positive for Listeria spp. No Listeria was detected in herring and horse mackerel. In catfish, L. welshimeri (13.7 %) was the most commonly isolated species followed by L. monocytogenes (11.8 %), L. innocua (9.8 %), L. grayi subsp. murrayi (9.8 %), L. grayi subsp. grayi (7.8 %), and L. ivanovii (3.9 %). In mackerel, only L. monocytogenes was detected in one sample.L. monocytogenes isolates serotyped as type 1 and type 4 (3 isolates each) and one non-typeable.Antimicrobial resistance profiling showed all L. monocytogenes isolates were resistant to ampicillin and tetracycline. Two were resistant to erythromycin. However, they were susceptible to rifampicin,vancomycin,chloramphenicol and streptomycin. Four virulence-associated genes (prfA, hlyA, actA and inlA) in addition to the genus gene (prs) were investigated using multiplex PCR. All the isolates were positive for prs gene but, onlyL. monocytogenes isolates were positive for all tested virulence genes. Our study indicates that imported raw catfish can represent a significant source of L. monocytogenes and potential health risk for listeriosis.
The aim of this study was to determine the differences concerning phenotypic and genotypic characters of L.monocytogenes isolated from different sources (100 meat, 100 offals, 100 fish and 100 ready to eat foods-RTE-which is represented by luncheon) on the basis of pathogenicity and antibiotic resistance. To achieve this aim, bacteriological examination was done according to ISO 11290 amendment 2004.then confirmed by biochemical reactions and serotyping, then antimicrobial susceptibility testing which indicates the presence of multidrug resistance isolates. Biofilm binding activity of the isolated L.monocytogenes isolates showed that three isolates had strong binding activity, two isolates showed moderate binding activity and one isolate was weak/non biofilm producer. The molecular characterization was done by detection of class1 integron and for pathogenicity by detection of the presence of hlyA gene which encodes listeriolysin of L.monocytogenes then sequencing of the resulted PCR product to determine the difference between the isolates. The confirmation of results was done by SYBR green Real-time PCR.
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