Microbiological evaluation of Thai fermented fish (pla-ra) production contact surfaces

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Anggita Ratri Pusporini
Patimakorn Pasuwan


Pla-ra is a lactic acid fermented fish product in Thailand, typically consumed as a side dish. Multiple outbreaks have been linked to the consumption of fermented foods, including pla-ra. During the fermentation process, pla-ra is in direct contact with a food container for an extended period which is also potentially contaminated with a high number of microorganisms. This research determined the prevalence of pathogenic bacteria on the surface of pla-ra production containers. From three different pla-ra manufacturers in Khon Kaen province, Thailand, 110 swab samples were collected from 25 pla-ra clay and polyethylene (PE) production containers. The samples, cultivated in selective media, were contaminated with Bacillus cereus (7.64 ± 0.13 log10 colony forming unit (CFU)/cm2), Clostridium perfringens (6.53 ± 0.21 log10 CFU/cm2), Escherichia coli (8.23 ± 0.15 log10 CFU/cm2), Salmonella spp. (5.73 ± 0.22 log10 CFU/cm2) and Staphylococcus aureus (7.81 ± 0.16 log10 CFU/cm2). The 16s rRNA sequencing analysis confirmed the presence of Klebsiella aerogenes, Clostridium perfringens, Escherichia coli, Listeria innocua, and Staphylococcus aureus. The population of each bacteria found on the surfaces was, respectively, 7.64 ± 0.18, 7.79 ± 0.14, 8.40 ± 0.24, 7.82 ± 0.14, and 8.18 ± 0.17 log10 CFU/cm2 in clay containers and 7.39 ± 0.24, 7.39 ± 0.26, 8.12 ± 0.08, 8.32 ± 0.15, and 8.46 ± 0.26 log10 CFU/cm2 in PE containers. The specific environmental conditions and the handling of raw materials, including contact time during fermentation and sanitation, affect the possibility of cross-contamination. These results highlight the importance of pasteurization of pla-ra to ensure its safety.


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