Food Sensing: Detection of Bacillus cereus Spores in Dairy Products

Abstract

Milk is a source of essential nutrients for infants and adults, and its production has increased worldwide over the past years. Despite developments in the dairy industry, premature spoilage of milk due to the contamination by Bacillus cereus continues to be a problem and causes considerable economic losses. B. cereus is ubiquitously present in nature and can contaminate milk through a variety of means from the farm to the processing plant, during transport or distribution. There is a need to detect and quantify spores directly in food samples, because B. cereus might be present in food only in the sporulated form. Traditional microbiological detection methods used in dairy industries to detect spores show limits of time (they are time consuming), efficiency and sensitivity. The low level of B. cereus spores in milk implies that highly sensitive detection methods should be applied for dairy products screening for spore contamination. This review describes the advantages and disadvantages of classical microbiological methods used to detect B. cereus spores in milk and milk products, related to novel methods based on molecular biology, biosensors and nanotechnology.

Characterization of Bacillus cereus in Dairy Products in China

“…contamination constantly arose in various milk products all over the world [ 61 , 62 , 65 , 66 , 67 , 68 ]. The prevalence of B. cereus in dairy products is difficult to estimate, and food poisoning incidents caused by B. cereus still remain a thorny problem worldwide due to the high tolerance of B. cereus to various environments and strong propagation capacity of B. cereus spores [ 2 , 5 , 13 , 47 , 69 ]. The B. cereus isolates correspondingly are suspected of threatening the safety of raw milk and dairy products in China [ 5 , 13 , 70 ].…”

“…Researches showed that 1g of soil contains 50–380,000 CFUs (colony-forming units) B. cereus spores, and 1 m 3 of air has at least 100 CFUs of B. cereus spores. Thus, the abundant B. cereus group spores in the environment are a major cause of the high prevalence rate of B. cereus [ 5 , 72 ]. B. cereus and its spores subsequently have a great opportunity to circularly contaminate dairy farms, human market, food supply places, and dairy products and colonize the intestinal tract of invertebrates and cause illness in humans afterwards ( Figure 3 a).…”

“…B. cereus or presumptive colonies of Bacillus are counted on the varieties of Bacillus agar by spiral-plating or spread-plating techniques, most probable number (MPN) method and so on [ 97 ]. Both B. cereus cells and spores in the examined products can be counted according to the colony-forming units (CFUs) [ 5 , 98 , 99 ]. In addition, B. cereus isolates have the capacity for casein, starch and tributyrin hydrolysis as well as lactose fermentation, which inspired the invention of chromogenic medium for B. cereus [ 100 , 101 ].…”

“…However, the detection techniques of B. cereus and its virulence factors are strongly limited [ 5 , 110 , 114 ], and B. cereus diagnostic method is still a field to be developed [ 135 ]. The widely used nucleic acid-based detection technology cannot accurately determine the bacterial activity and toxin expression [ 110 , 114 ].…”

“…Foodborne outbreaks involving B. cereus in China usually occurred through dairy products [ 12 , 13 , 14 , 15 ]. Major symptoms of food-poisoning caused by B. cereus are divided into either diarrhea or emesis [ 5 , 16 ]. Diarrhea is mainly induced by three enterotoxins that belong to the family of pore-forming toxins (PFTs) [ 17 ], including non-hemolytic enterotoxin (Nhe) [ 18 , 19 ], hemolysin BL (Hbl) [ 20 ] and cytolysin K (CytK) [ 21 ], while the emetic syndrome is tightly connected to a lethal toxin known as “cereulide”, which is synthesized by a non-ribosomal peptide synthetase (NRPS) encoded by a ces gene [ 22 , 23 ].…”