POLYMERASE CHAIN REACTION FOR THE CONFIRMATION OF ISOLATED LISTERIA SPP. FROM FOOD CONTACT SURFACES IN THE OPEN MARKETS IN KHONKAEN, THAILANDP. PASUWAN, R. R. BEUMER, H. DEN BESTEN AND B. LEENANON
Swab samples (280) were taken from different kinds of food contact surfaces including stainless steel, tile, polyethylene and wooden cutting board from five open markets in KhonKaen, Thailand. Listeria spp. was found from food contact surfaces in three open markets. Most positive samples were isolated from surfaces of stainless steel, wooden cutting board, ceramic tile and polyethylene. All suspected colonies were identified using biological tests such as Gram stain, mobility, catalase, and CAMP Tests. The weak hemolytic colonies of the CAMP reaction on 5% sheep blood agar defined that 13 out of 70 colonies were identified as L. monocytogenes. Listeria identification tests were performed by 10 Listeria API strips. All weak hemolytic strains were confirmed by PCR. PCR products amplified with 16sRNA primers were sent for sequencing. Results showed that all isolated strains amplified with the general Listeria primer were confirmed as Listeria spp. However, the PCR products bands which were amplified specifically for L. monocytogenes were missing on 1.5% Agarose gel. The PCR results implied that all isolated strains were not L. monocytogenes. Blasting results from EMBL-EBI and Ezbiocloud databases reported that all isolated strains with weak hemolytic results were L. innocua.
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