Isolation and enumeration of Bacillus cereus in raw milk distributed in Tabriz, Iran and detection of ces gene among the isolates

Document Type : Research Paper


1 M.Sc Student of Microbiology, Cellular and Molecular Biology Department, Institute of Rabe-Rashidieh, Tabriz, Iran.

2 Associate Professor of Department of Food Hygiene, Tabriz Branch, Islamic Azad University, Tabriz, Iran


Bacillus cereus is a gram-positive and spore-forming bacterium which is widely distributed in nature. It also has been known as a major food borne pathogen that often plays a role in the contamination of ready-to-eat and dairy products. It causes two different types of food poisoning in human: the diarrheal type and the emetic type. The aim of this study was to isolate and enumerate B. cereus in raw milk distributed in the stores of Tabriz city, Iran and to detect ces gene among the isolates. For this purpose, 120 samples of raw milk were randomly selected from the stores during February to June 2017. They were transferred to the Laboratory of food hygiene under sterile conditions in order to isolate, identify and enumerate B. cereus according to the national standard method of Iran and PCR. According to the results of microbial culture, out of 120 samples of raw milk, 13 (10.83%) samples were contaminated with B. cereus and the mean rate of contamination was 2.8 log10/ml. PCR results showed that of 13 positive samples, 12 (92.3%) samples contained ces gene which is responsible for vomiting. The results of this study showed that raw milk has the potential for human intoxication by B. cereus; and the use of procedures to reduce the bacterial contamination during the processing of dairy product is required.


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