Study of entering of Listeria monocytogenes into Viable But Non Culturable form during heat treatment process of foods

Reza I, Masoud; Forozandeh Moghadam, Mahdi; Mojtaba Mobarez, Ashraf; Hosseini, Hedayat; Zolfaghari, Mahdi

Study of entering of Listeria monocytogenes into Viable But Non Culturable form during heat treatment process of foods

Authors

Masoud Reza i

Mahdi Forozandeh Moghadam

Ashraf Mojtaba Mobarez

Hedayat Hosseini

Mahdi Zolfaghari

Abstract

Listeria monocytogenes is one of the most dangerous bacteria in food products which caused about 20 to 30% fatalities. One of the major foods which caused listeriosis is ready to eat (RTE). So, appropriate heating processing methods are need for elimination of L. monocytogenes. These bacteria has ability entering into viable but nonculturable (VBNC) form in unfavorable conditions. So this investigation was aimed to considering behavior of this pathogen at higher temperatures from recommended for elimination of these bacteria. For this purpose, bacteria in 5×10⁶ counts in mid log phase were inoculated into two medium BHI Broth and fish Broth (FB) and they exposed to 85 ºC for 10 minutes. Direct plate count on listeria choromogenic agar, BacLight^® Live/Dead and gene expression of 16S rRNA, the housekeeping gene, were done before and after heat shock. The results show that these bacteria lose their culturability during high heat shock. The results of fluorescent dyes showed the viability of these bacteria after heat shock (p< 0.01). The results of gene expression considering confirmed the results of fluorescence dyes and showed that 16S rRNA gene was expressed in nonculturable bacteria. According to these results, there is a big question on the D value on quality control for these bacteria in food processing processes, especially for RTE foods.

Keywords

VBNC

Listeria monocytogenes

Gene expression

Food safety

High temperature