Molecular-based detection of pathogenic Listeria spp. in Philippines raw carabao's milk and white cheese
2017
Belen, R.H. | Elegado, F.B. | Perez, M.T.M. | Calapardo, M.R. | Mendoza, B.C.
This study was conducted to detect the presence of pathogenic Listeria species in locally produced white cheese (quesong puti) and raw carabao's milk samples from Laguna, Nueva Ecija, Bulacan, Rizal, Lucena City, and Makati City, Philippines using phenotypic and molecular analyses. Out of 208 initial isolates obtained from 31 dairy products samples, 118 isolates were preliminarily considered presumptive Listeria species based on established culture-based detection methods. Further phenotypic tests and growth efficiency assessment using highly selective Polymyxin Acriflavine Lithium chloride Ceftazidime Aesculin Mannitol (PALCAM) agar narrowed them down to only five putative isolates. However, the Polymerase Chain Reaction (PCR) analysis using the primer pairs Lis and LL1/LL4 for the listeriolysin O gene and iap for the invasion-associated protein gene yielded negative results for the potentially pathogenic Listeria spp., except for the ARKPC49 isolate. The isolate, which was identified as Providencia sp. Through 16s ribosomal DNA (rDNA) sequence analysis, was found to have variant PCR amplicons. Cluster analysis also confirmed its unrelatedness to Listeria spp. Four other isolates (e.g., LKPC48, LC3C37, LC2C29 and LC2C42) which exhibited gray-green colonies with a black halo on PALCAM Agar were identified as Corynebacterium vitarumen. Thus, the results confirmed the absence of pathogenic Listeria spp. and highlighted the need for molecular methods to supplement cultural methods in detecting pathogenic Listeria spp. from dairy products.
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