Enumeration and molecular detection of Bacillus cereus in local indigenous and imported rice grains

Food poisoning caused by Bacillus cereus is frequently associated with consumption of contaminated fried rice. The foodborne bacteria produce endospore which is resistant towards heat. They are able to grow in the temperature of 10–48 °C, and temperatures ranging from 28 to 35 °C are the optimum. To date, the available treatments for the disinfection are used which are high temperature for canning and lowering pH [6]. B. cereus pathogenesis depends on amount of dose consumed and site of the bacteria producing toxin in either food or intestine [16]. The bacterial infection is manifested with diarrhoea and emesis.

Local rice in Sarawak contributes 214.97 tonne valued at RM 369,551 representing 3.7% of the total export value of agricultural product [8]. Rice cultivation in Sarawak had always been on a subsistence cash crop basis with low yields because of tough hilly terrains, drought, poor drainage and irrigation and lack of modern machinery usage. Rice is cultivated manually using traditional methods, and in some places, machinery is used to increase the yield. In spite of these setbacks, the local farmers had produced some of the world finest and very best home-grown aromatic rice. Notable traditional rice produced in Sarawak are the Bario rice, Biris rice, Bajong rice, Beras Hitam or black rice and Beras Merah or red rice. There are other aromatic rice varieties, namely Kanowit rice, Wangi rice, Rotan rice, Bali rice, Mamut rice, Selasih rice, Kateh Merah, Lemak rice and the black glutinous rice. As the society became more affluent and health conscious, focus now has shifted to the local pesticide-free produce and high nutritional value [15]. In tandem with food security and fulfilment of the requirement of rice by Malaysians, imported rice is also retailed in markets. The most demanded imported rice in Malaysia are Thai White Rice and Vietnamese White Rice [4].

The gyrB gene encodes subunit B protein of DNA gyrase (topoisomerase type II), which is essential for DNA replication [3]. The gene is used in phylogenetic and taxonomic analysis since it is ubiquitous even in different bacterial species. Furthermore, the gene has better efficiency than its counterpart, 16S rRNA because of faster evolutionary rate which contributes to lesser percentage of gene similarities, even among closely related species [19] and therefore suitable for bacterial species identification. A study conducted by Bavykin et al. [3] showed that the percentage of gene similarity of 16S rRNA in closely related species can be up to 100%, which makes it hard to distinguish between the species. By comparison, Wang et al. [19] stated that the percentages of gene similarity of gyrB between the species are up to 99.2%. Up to the present time, Malaysia has not had any official statistics on B. cereus outbreak, but there are a few reports regarding incidences of B. cereus in food such as ready-to-eat cereals [5], raw and cooked chicken meats [1] and ready-to-eat cooked rice [17] and cooked rice [12]. There has been no study of B. cereus in imported rice in Malaysia. This shows screening of B. cereus from food is crucial and positive findings may help further initial preventative measures of outbreak from occurring.