Mai Van Muoi, director of the Quang Nam Province Department of Health, said Thursday that of the 12 samples sent to Nha Trang Pasteur Institute, seven were found to have the two bacteria, both leading causes of food poisoning.
But the department has yet to conclude if the bacteria were the main cause of the food poisoning suffered by the 150 diners, including 33 foreign tourists, last week. All have been discharged from hospital.
Bacillus cereus was found in the samples of pork bologna while salmonella was found in char siu made from pork.
Both were found in shumai and fresh vegetables.
The bacteria cause high fever, headache, fatigue, loss of appetite, and violent diarrhea.
If not treated promptly, they could lead to dangerous complications and even death due to dehydration.
Salmonella can survive in water for two to three weeks and in excrement for two to three months, but is destroyed within five minutes at 100 degrees Celsius or with common disinfectants.
Bacillus cereus is widespread in the environment and therefore could easily contaminate food. It has the ability to resist to high heat.
The main transmission routes of these bacteria are undercooked foods and improper processing of raw foods.
Poor sanitation that involves unsafe water and substandard drainage systems also enables transmission.
On September 11, when the food poisoning episode occurred, the shop had sold over 1,900 sandwiches.
The owner, Truong Thi Phuong, 60, told VnExpress that she personally supervises the entire process of buying raw materials and processing and selling them every day.
She buys the breads from a bakery near her house and vegetables and ingredients made from pork like pate, shumai and char siu from Hoi An Market.
Her staff make the egg sauce.
Her husband has made the food and she has supervised it for 34 years, and the staff only wash vegetables and handle customers.
A team of health inspectors that visited the eatery on September 13 said its cooking area did not meet hygiene requirements, and it stored raw materials and food together.
Ms. Phuong has been selling banh mi, the typical Vietnamese baguette sandwich, for 34 years and is popular among foreign tourists.