Detection of actA gene in Listeria monocytogenes isolated from dairy products

Subject Areas : Bacteriology

Jamileh Norowzi ¹ (Professor, Department of Microbiology, North Tehran Branch, Islamic Azad University, Tehran, Iran.)
Soheila Moradi Bidhendi ² (Assistant Professor, Department of Microbiology, North Tehran Branch, Islamic Azad University, Tehran, Iran.)
Marzieh Shafiee ³ (MS.c., Department of Microbiology, North Tehran Branch, Islamic Azad University, Tehran, Iran.)

Received: 2012-11-20 Accepted : 2013-02-10 Published : 2013-10-01

Keywords: PCR, Listeria monocytogenes, actA gene, Congo red phenotype,

Abstract :

Background and Objectives: Listeria is a gram-positive facultative intracellular bacteria. The actA is one of the most important genes in this bacterium, which involves in bacterial movement in the host cell and so in its pathogenesis. The purpose of this study is to evaluate the actA gene in Listeria monocytogenes strains isolated from dairy products. Materials and Methods: This cross sectional study was performed on 70 samples of dairy products collected from Tehran and Babolsar, Iran from June to August 1391. The samples were grown onto BHI agar and Mueller agar. A PCR approach was used to detect the presence of the actA gene in the isolated Listeria species. Also, the isolated were grown into TSA containing 0.0015% Congo red in order to determine the invasive properties of L. monocytogenes. Results: This study showed contamination of the milk, cheese and soft cheese samples with L. monocytogenes (10 cases), L. innocua (4 cases), L. welshimeri (2 cases) and L. seeligeri (1 case). Furthermore, no yogurt and butter samples were contaminated with Listeria. Although all of these isolates contained actA gene in their genome, only 14% of the strains isolated from vegetables were positive for this gene. A total of 10 cases of isolated L. monocytogenes, 100% of the clinical strains, 70% of the strain food and 100% of standard strains purchased from Razi Institute were positive for Congo red phenotype. Conclusion: According to the results obtained in this study, detection of actA gene based on PCR can be used as an alternative approach for identification of pathogenic L. monocytogenes in samples without culture method. Also, due to the widespread use of dairy by individuals, it seems necessary to reduce bacterial contamination monitoring the production process, transport and distribute this material.

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