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MPN-PCR detection and antimicrobial resistance of Listeria monocytogenes isolated from raw and ready-to-eat foods in Malaysia

Marian, M.N., Sharifah Aminah, S.M., Zuraini, M.I., Son, R., Maimunah, M., Lee, H.Y., Wong, W.C., Elexson, N.
Food control 2012 v.28 no.2 pp. 309-314
Listeria monocytogenes, ampicillin, antibiotic resistance, food contamination, food pathogens, genes, listeriosis, markets, microbial load, minced meat, monitoring, polymerase chain reaction, raw foods, ribosomal RNA, sausages, selective media, streptomycin, virulence, Malaysia
Listeria monocytogenes is a major food-borne pathogen with an opportunistic character that is able to cause severe human listeriosis worldwide. The surveillance and detection system concerning food safety in the country needs to be improved. Therefore, it was a primary aim of this study to provide a general baseline on the L. monocytogenes contamination in foods from local markets. A total of 140 raw and ready-to-eat food samples were analyzed by plating on selective PALCAM media and the suspected colonies were confirmed by MPN-PCR technique. Positive isolates were evaluated for their susceptibility to 8 commonly used antibiotic agents by using disc diffusion assay. The isolated strains yield PCR products of 938 bp 16S rRNA gene and 701 bp hylA virulence gene specific for L. monocytogenes. The microbial load of L. monocytogenes was found to range from <3 to 1100 MPN/g with most of the samples (94.3%) had microbial load of <100 MPN/g. L. monocytogenes was detected in 8.57% of foods samples which 33.3%, 25%, and 13.3% were detected in burgers, minced meat and sausages respectively. The isolates showed high resistance against ampicillin and penicillin G (100%), whereas high susceptibility was showed toward streptomycin (100%). The molecular approaches used in this study provide highly sensitive and specific results which were very easy and fast to perform. These findings also suggested that the L. monocytogenes contamination in local foods is relatively low. However, it highlighted the emergence of antibiotics multi-resistant Listeria spp. in the environment.