Cereus Contamination Research Articles

Isolation and selection of Bacillus cereus specific phages from hospital wastewater

Abstract. Rovik A, ‘Aziz S, Pramono H. 2020. Isolation and selection of Bacillus cereus specific phages from hospital wastewater. Biodiversitas 21: 2871-2877. Bacillus cereus (B. cereus) is a pathogenic bacterium that frequently contaminates food by producing entero and emetic toxins. B. cereus has shown resistance to various antibiotics, especially β-lactam antibiotics. An alternative to control B. cereus contamination is the use of bacteriophages. This study aimed to isolate and screen B. cereus specific phages from hospital wastewater in Banyumas District. The research was conducted descriptively through isolation, purification, titer determination, host ranges, and adsorption rate determination. A total of 29 isolates of B. cereus-phages were isolated from hospital wastewater in Banyumas with various titers, ranged from 0.14-3.76 x 107 PFU.mL-1. Isolated phages could be grouped into two, narrow host range (14 phages) and broad activity spectra (15 phages) that infect both Gram-positive and negative bacteria i.e. B. subtilis, B. fragilis, B. licheniformis, Citrobacter freundii, Klebsiella pneumoniae, Salmonella thypi, and Escherichia coli. The infections had a latency period of 60-120 minutes. The decrease of culture absorbance value ranged from 0.06 to 0.41, while the control tended to increase by 0.39. The largest decreases were showed by phage isolates RSBMS-2 and RSBMT-1 with 0.41 and 0.37, respectively.

Bacillus cereus contamination of pasteurized human milk donations: frequency, origin, seasonal distribution, molecular typing of strains and proposed corrective/preventive actions

Objectives An increase in pasteurized human milk contamination with Bacillus cereus was witnessed in milk donated to the Amiens-Picardie Human Milk Bank over the 2017–2018 period. To better understand the origin of such an increase, this study aimed to describe the frequency of Bacillus cereus contamination in anonymous and personalized human milk donations of Amiens Human Milk Bank in 2018, compare the genetic profiles of Bacillus cereus strains found in pasteurized human milk and set up corrective/preventive actions to reduce Bacillus cereus contamination. Study design A retrospective cohort study of human milk donated from January to December 2018 was set. Data on the microbiological quality of donated human milk and genetic profiles of Bacillus cereus strains isolated from pasteurized donated human milk and the environment were collected. Results The overall noncompliance rate related to the microbiological quality in the 1585 batches of analyzed human milk donations was of 27.3%. Post-Holder pasteurization, rejection rates were significantly higher for anonymous donations as compared to personalized ones. Bacillus cereus was the main cause of noncompliance. Bacillus cereus contaminations could not be attributed to a single strain spreading through Amiens human milk bank and Amiens hospital environment as the genetic profiles of the collected strains were different. Corrective actions led to a decrease in the noncompliance rate due to Bacillus cereus (37.7–9.7%) post-Holder pasteurization. Conclusion Bacillus cereus was the primary cause of rejection for pasteurized human milk donations over the investigated period. These contaminations did not originate from the spread of a single strain. A first round of corrective actions enabled a fair decrease in Bacillus cereus contaminations.

Microbial indices of industrial and traditional medicinal herbs in Ahvaz, Iran

Introduction. Medicinal herbs are susceptible to microbial contamination which can have profound effects on the consumer’s health. Our study aimed to evaluate microbial contamination of common medicinal herbs in Ahvaz.
 Study objects and methods. We collected 80 samples of traditional and industrial medicinal plants from the supply market, namely valeriana, fennel, licorice, and shirazi thyme. The reference method was used to determine microbial indices such as the total count of microorganisms, yeast and mold, Bacillus cereus, coliforms, and Escherichia coli.
 Results and discussion. We found that the total microbial count, yeast and mold, B. cereus, and coliform contamination accounted for 45, 77, 55, and 55% of the total samples, respectively, exceeding the allowed limits. There was a significant difference between the industrial and traditional samples in fungal and coliform contamination, with the traditional samples being more highly contaminated. However, no significant difference was observed between them in total count and B. cereus contamination. E. coli contamination was detected in 31.2% of the samples, mostly in traditional. Total microbial count and yeast and mold contamination were highest among valeriana plants. Fennel showed the highest B. cereus and coliform contamination. The lowest contamination was observed in licorice.
 Conclusion. The results showed that a considerable percentage of the medicinal herbs under study were contaminated at levels exceeding the standard limits. Plants could be contaminated during harvesting, processing or storage. Finally, different species of plants have different antimicrobial activities that affect their microbial contamination.

Lab-Made Electronic Nose for Fast Detection of Listeria monocytogenes and Bacillus cereus.

The aim of this study is to determine the performance of a lab-made electronic nose (e-nose) composed of an array of metal oxide semiconductor (MOS) gas sensors in the detection and differentiation of Listeria monocytogenes (L. monocytogenes) and Bacillus cereus (B. cereus) incubated in trypticsoy broth (TSB) media. Conventionally, the detection of L. monocytogenes and B. cereus is often performed by enzyme link immunosorbent assay (ELISA) and polymerase chain reaction (PCR). These techniques require trained operators and expert, expensive reagents and specific containment. In this study, three types of samples, namely, TSB media, L. monocytogenes (serotype 4b American Type Culture Collection (ATCC) 13792), and B. cereus (ATCC) 10876, were used for this experiment. Prior to measurement using the e-nose, each bacterium was inoculated in TSB at 1 × 103–104 CFU/mL, followed by incubation for 48 h. To evaluate the performance of the e-nose, the measured data were then analyzed with chemometric models, namely linear and quadratic discriminant analysis (LDA and QDA), and support vector machine (SVM). As a result, the e-nose coupled with SVM showeda high accuracy of 98% in discriminating between TSB media and L. monocytogenes, and between TSB media and B. cereus. It could be concluded that the lab-made e-nose is able to detect rapidly the presence of bacteria L. monocytogenes and B. cereus on TSB media. For the future, it could be used to identify the presence of L. monocytogenes or B. cereus contamination in the routine and fast assessment of food products in animal quarantine.

A Study on Prevalence and Characterization of Bacillus cereus in Ready-to-Eat Foods in China.

Bacillus cereus is widely distributed in different food products and can cause a variety of symptoms associated with food poisoning. Since ready-to-eat (RTE) foods are not commonly sterilized by heat treatment before consumption, B. cereus contamination may cause severe food safety problems. In this study, we investigated the prevalence of B. cereus in RTE food samples from different regions of China and evaluated the levels of bacterial contamination, antibiotic resistance, virulence gene distribution, and genetic polymorphisms of these isolates. Of the tested retail RTE foods, 35% were positive for B. cereus, with 39 and 83% of the isolated strains harboring the enterotoxin-encoding hblACD and nheABC gene clusters, respectively. The entFM gene was detected in all B. cereus strains. The cytK gene was present in 68% of isolates, but only 7% harbored the emetic toxin-encoding gene cesB. Antimicrobial susceptibility testing revealed that the majority of the isolates were resistant not only to most β-lactam antibiotics, but also to rifamycin. Multilocus sequence typing (MLST) revealed that the 368 isolates belonged to 192 different sequence types (STs) including 93 new STs, the most prevalent of which was ST26. Collectively, our study indicates the prevalence, bacterial contamination levels, and biological characteristics of B. cereus isolated from RTE foods in China and demonstrates the potential hazards of B. cereus in RTE foods.

Risk Comparison of the Diarrheal and Emetic Type of Bacillus cereus in Tofu.

We investigated the ability of biofilm formation, survival, and behavior of diarrheal and emetic Bacillus cereus vegetative cells and spores in tofu. Both diarrheal and emetic B. cereus did not proliferate at a temperature below 9 °C in tofu. However, the emetic B. cereus grew faster than diarrheal B. cereus at 11 °C and had better survival ability at low temperatures. Both diarrheal and emetic B. cereus were able to form a biofilm on stainless steel. These biofilm cells were transferred to tofu in live state. The transferred biofilm cells could not grow at a temperature below 9 °C but grew over 11 °C, like planktonic cells. B. cereus contamination in tofu at a high concentration (>6 logs CFU/g) was not entirely killed by heating at 80, 85, or 90 °C for 2 h. Spores and emetic B. cereus had higher resistance to heat than vegetative cells and diarrheal B. cereus, respectively.

Prevalence of the Strains of Bacillus cereus Group in Artisanal Mexican Cheese.

Bacillus cereus is a microorganism associated with food poisoning. It has been found in products, such as milk and dairy products. The aim of this study was to isolate and identify B. cereus group strains in artisan cheeses sold in southwestern Mexico, as well as its toxigenic profile, its psychrophilic ability, and its biofilm production. B. cereus isolation was performed on Mannitol Yolk Polymyxin (MYP) agar and this was molecularly confirmed by the amplification of the gyrB gene. Polymerase chain reaction was used to determine the toxigenic profile, amplifying conserved regions of hblABD and nheABC operons, which code for the subunits of Hbl and Nhe toxins, respectively, as well as ges and cytK genes, which code for toxin cereulide and cytotoxin K (Cytk). Frequency of B. cereus contamination in artisan cheeses was 29.48% (23/78), and the bacterium was isolated in similar quantities in all types of products. All strains were amylase positive, and 60.86% (14/23) were able to produce biofilm; 91.30% (21/23) of the strains were psychrophilic. In most of the strains, at least one gene related to enterotoxins was identified (21/23). B. cereus strains in this study have a high toxigenic potential, which increases the risk of food poisoning due to the consumption of artisan cheeses made in Mexico.

Contamination of Bacillus cereus in Elementary School Snack Food

Many food snacks have the advantage but still have health risks as evidenced by the many cases of food poisoning, one of the causes of food poisoning is Bacillus cereus. This study aims to determine the amount and percentage of Bacillus cereus pollution on snacks sold in elementary schools. This research is expected to provide information to the public about the presence or absence of bacteria Bacillus cereus contamination. This research uses purposive sampling technique. The sample used in this study was hawker food sold in Elementary School as many as 20 samples consisting of 10 samples that have not fried and ten samples that have cooked. The results of the questionnaire study showed 83% of sellers did not put snacks in closed containers and found Bacillus cereus in meals. Conclusion 9 (45%) of food samples contaminated with Bacillus cereus bacteria

OCCURRENCE AND TOXIN GENE PROFILE OF BACILLUS CEREUS IN DAIRY PRODUCTS

Bacillus cereus, a bacteria frequently associated with food spoilage, is responsible for 2 different foodborne illness in humans: a diarrheal disease, associated with cytotoxin K, hemolysin BL and a non-hemolytic enterotoxin, and an emetic syndrome, associated with the cereulide toxin. The aim of this study is to investigate the occurrence of B. cereus in 515 hard and soft cheeses collected in southern Italy. The strains were molecularly characterized for the presence of hblA, hblC, hblD, nheA, nheB, nheC, cytK, and entFM genes, related to the production of enterotoxins (trimeric hemolysin BL, trimeric non-hemolytic enterotoxin, cytotoxin K and enterotoxin FM). One hundred thirty eight samples (26.8%) were found contaminated by B. cereus. One hundred of the contaminated samples (72.5%) showed a level of B. cereus contamination ≤103 CFU/g, whereas 9 (6.5%) samples showed a contamination >105 CFU/g. Seven different molecular profiles were found among the 138 strains of B. cereus isolated. The most common profile was nheABC-entFM, found in 42 strains, followed by the hblACD-nheABC-cytK-entFM, found in 33 strains, the nheABC-cytK-entFM, found in 24 strains, the hblACD-nheABC-entFM, found in 11 strains, the hblACD-nheAC-entFM, found in 15 strains, and the nheC-entFM, found in 12 strains. Eleven strains did not harbored any of these genes. In 7.2% (37/515) of samples, characterized by a bacterial contamination >103 CFU/g, we found B. cereus strains harboring genes encoding for at least one complete enterotoxin.

Contaminated feed-borne Bacillus cereus aggravates respiratory distress post avian influenza virus H9N2 infection by inducing pneumonia

Avian influenza virus subtype H9N2 is identified in chickens with respiratory disease while Bacillus cereus (B. cereus) has been frequently isolated from chicken feed in China. However, the roles of co-infection with these two pathogens remain unclear. In the present study, SPF chicks were intragastrically administered with 108 CFU/mL of B. cereus for 7 days and then inoculated intranasally with 100 EID50 of H9N2 three days later. Alternatively, chickens were initially inoculated with H9N2 and then with B. cereus for one week. Post administration, typical respiratory distress persisted for 5 days in both co-infection groups. Gizzard erosions developed in the groups B. cereus/H9N2 and B. cereus group on 7th day while in group H9N2/B. cereus on 14th day. More importantly, both air-sac lesions and lung damage increased significantly in the co-infection group. Significant inflammatory changes were observed in the B. cereus group from day 7 to day 21. Moreover, higher loads of H9N2 virus were found in the co-infected groups than in the H9N2 group. Newcastle Disease Virus (NDV) specific antibodies were decreased significantly in the H9N2/B. cereus group compared to the B. cereus and the B. cereus/H9N2 groups. Nonspecific IgA titers were reduced significantly in the B. cereus group and the H9N2/B. cereus group compared to the control group. In addition to this, lower lymphocyte proliferation was found in the con-infection groups and the H9N2 group. Hence, feed-borne B. cereus contamination potentially exacerbates gizzard ulceration and aggravates H9N2-induced respiratory distress by inhibiting antibody-mediated immunity and pathogen clearance. Thus controlling the B. cereus contamination in poultry feed is immediately needed.

Removal of B. cereus cereulide toxin from monoclonal antibody bioprocess feed via two-step Protein A affinity and multimodal chromatography

A rapid and sensitive liquid chromatography-mass spectrometry assay was developed and used to quantify emetic cereulide peptide exotoxin, which can be related to possible Bacillus cereus contamination in monoclonal antibody (mAb) bioprocess feeds. The assay limit of detection was 0.05 ng/mL (~1 fmol injected) and limit of quantification 0.16 ng/mL (~3 fmol injected) over a standard curve with >3 orders of magnitude linear dynamic range. The assay allowed quantification of toxin removal in an established two-step mAb purification process consisting of Protein A affinity chromatography followed by multi-modal anion exchange chromatography. Toxin content was ascertained in process stream sample fractions as well as on the Protein A affinity column. An optimized analytical method allowed separation of cereulide toxin from other mAb cell culture components within 6 min. Spiking experiments showed that samples should be collected in high (80% v/v) content acetonitrile to reduce nonspecific losses of the cereulide. The majority of mAb purification process-associated cereulide was detected in the Protein A flow through fraction, whereas only residual amounts were found in wash, strip, and elution fractions. Column cleaning-in-place (CIP) procedures were evaluated to prevent carryover between affinity capture cycles. No carryover was detected between cycles, however trace amounts of cereulide were extracted from the Protein A resin. Increasing the CIP NaOH concentration from 0.1 M to 0.5 M, and contact time from 15 min to 1 h, improved removal of residual cereulide from the resin. Applicability of CIP clearance of cereulide during Protein A chromatography was confirmed with three different mAb feeds. Post Protein A polishing, via target flow through on a multi-modal anion exchange chromatography column, resulted in a product pool with no detectable cereulide. Approximately 5 logs of reduction in cereulide concentration was obtained over the two-step chromatography process. Cereulide contamination is well known and of concern in food processing, however this research may be the first LC-MS quantification of cereulide contamination, and its clearance, in biopharmaceutical mAb processing. The analytical method may also be used to rapidly screen for cereulide contamination in upstream cell culture process streams, prior to downstream product purification. This will allow appropriate measures to be taken to reduce toxin exposure to downstream bioprocess raw materials, consumables and equipment.

Microbial quality of reduced-sodium napa cabbage kimchi and its processing.

This study evaluated the microbial safety of reduced‐sodium napa cabbage kimchi products by comparing with conventional kimchi samples. Five commercial kimchi samples were collected from different manufacturers in Korea. Total aerobic plate counts and coliforms counts between regular and reduced‐sodium kimchi were not significantly (p > 0.05) different and major foodborne pathogens, including Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, and Yersinia enterocolitica were not detected in any sample. Bacillus cereus contamination among all kimchi samples was less than the regulation level (3.0 log CFU/g). However, high levels of coliforms were observed in both types of samples. To investigate microbial hazards of kimchi processing, we analyzed specific kimchi production processes and found five control points which can reduce coliform levels in kimchi samples. The results of this study could be helpful for the kimchi industry to produce safe reduced‐sodium kimchi products.

Supplementation of Modified Mannitol-Yolk-Polymyxin B Agar with Cefuroxime for Quantitative Detection of Bacillus cereus in Food.

The presence of unwanted competing flora has been the most common confounding factor in the enumeration of Bacillus cereus (B. cereus) using selective media such as mannitol-yolk-polymyxin B agar (MYPA). The objective of this study was to improve MYPA selectivity for B. cereus by supplementation with a second-generation cephalosporin, cefuroxime. The performance of cefuroxime-supplemented MYPA (cefu-MYPA) was evaluated by comparison with original MYPA in 60 food products with established microbiological standards for B. cereus contamination. Cefu-MYPA demonstrated superior recoverability and selectivity for B. cereus compared with original MYPA in most tested foods. B. cereus numbers on MYPA and cefu-MYPA were 363.5 and 462.0 CFU/g, respectively. Competing flora on cefu-MYPA was detected in significantly less samples (70%) compared to original MYPA (93%). In addition, the detection and isolation of suspected colonies were significantly improved in cefu-MYPA because of the reduction or elimination of competing flora in all tested foods except fruit juice, indicating superior selectivity of the modified medium. Our findings suggest that cefuroxime supplementation of MYPA would markedly improve the detection rate of B. cereus, particularly in foods with high levels of indigenous flora.

Short communication: Source tracking Bacillus cereus in an extended-shelf-life milk processing plant using partial sequencing of rpoB and multilocus sequence typing

We used rpoB partial sequencing and multilocus sequence typing (MLST) to characterize 7 Bacillus cereus strains obtained at the following points: ESL milk during shelf life, pasteurized milk, raw milk, and filler nozzles after cleaning in place. The objective of the study was to determine relatedness among B. cereus isolates from several sampling points along an ESL processing plant with the aim of source tracking. The study revealed that isolates from filler nozzles shared 100% similarity with isolates from ESL milk and raw milk using rpoB sequencing. It also revealed that isolates from pasteurized milk shared 100% similarities with isolates from filler nozzles and ESL milk using MLST. We suggest 3 routes of B. cereus contamination in ESL milk. We showed that B. cereus contamination of ESL milk might be through raw milk and biofilms from filler nozzles. In addition, rpoB partial sequencing and MLST can be used as tools for source tracking in ESL milk processing.

Prevalence of Bacillus cereus in powdered infant and powdered follow-up formula in China

Outbreaks and sporadic cases of foodborne disease caused by Bacillus cereus have been reported in China, including cases involving infants and children. However, the prevalence of B. cereus contamination in foods is not clearly known. In China, no legal microbiological criteria for B. cereus in powdered infant formula (PIF) and powdered follow-up formula (PFUF) currently exists. The purpose of the study was to investigate the prevalence of Bacillus cereus in PIF and PFUF sold in China and to provide data that could be used for risk assessment and management to ensure the safety of these kinds of products. As part of the national surveillance program, 6656 samples of PIF and PFUF were collected quarterly from urban and rural markets in 31 provincial-level administrative units in China in 2014. The results show that 7.53% of the samples were contaminated with B. cereus ≥10 CFU/g and 1.11% of the samples were contaminated above 100 CFU/g. There were no statistical differences of B. cereus contamination levels between PIF and PFUF or between samples taken from retail, wholesale and online outlets. The prevalence of B. cereus-positive samples differed between sampling regions and production regions. The occurrence of B. cereus >10 CFU/g of samples produced in summer and autumn, which were 8.80% and 9.18%, respectively, were higher than those in spring and winter, which were 6.67% and 6.32%, respectively. The study indicated a need to conduct further research on B. cereus contamination in powdered formula products in China before microbiological criteria are developed.

시중 유통 중인 젓갈의 미생물학적 안전성 평가

This study investigated the prevalence of total aerobic bacteria, coliform and food poisoning (Bacillus cereus) bacteria in commercial Jeotgal for the evaluation of microbiological safety. The mean mass of total aerobic bacteria was 4.8±1.4 log CFU/g in Jeotgal. Coliform was detected in 17 (48.6%) of 35 seasoned Jeotgal; 14 (42.4%) of 33 low salted Jeotgal compared with three (16.7%) of 18 general salted Jeotgal; and in three (37.5%) of eight HACCP certificated Jeotgal compared with 14 (32.6%) of 43 non-HACCP certificated Jeotgal. Bacillus cereus was detected in two (12.5%) of 16 non-seasoned Jeotgal compared with 20 (57.1%) of 35 seasoned Jeotgal; in 19 (57.6%) of 33 low salted Jeotgal compared with three (16.7%) of 18 general salted Jeotgal, and in four (50.0%) of eight HACCP certificated Jeotgal compared with 18 (41.9%) of 43 non-HACCP certificated Jeotgal. Overall, our results showed that coliform and B. cereus contamination was highest in the seasoned and low salted Jeotgal. It is necessary to improve the microbiological safety low salted and seasoned Jeotgal. The HACCP system in Jeotgal is reconfirmed for the enhancement of microbiological safety.

Monitoring of Sulfur Dioxide, Carotenoid Contents and Bacillus cereus Contamination of Dried Sweet Potato in Circulating Dried Agricultural Products

Monitoring of Sulfur Dioxide, Carotenoid Contents and Bacillus cereus Contamination of Dried Sweet Potato in Circulating Dried Agricultural Products

Contamination and characterization of multiple pathogens in powdered formula at retail collected between 2014 and 2015 in China

A total of 119 powdered formula samples collected from supermarkets, E-shops and online maternal counters in 16 provinces in China between 2014 and 2015 were analyzed for Cronobacter, Bacillus cereus, Clostridium sporogenes, Salmonella and Staphylococcus aureus. Antimicrobial susceptibility of Cronobacter was also tested by a broth microdilution method. Virulence genes related to emetic and diarrheal toxins production harbored by B. cereus were detected by multiplex PCR. The results showed that the prevalence of Cronobacter, B. cereus, C. sporogenes contamination were 3.4%, 36.1% and 9.2%, respectively. The contamination level of Cronobacter ranged from 0.36 MPN/100 g to 15 MPN/100 g. All Cronobacter isolates cultured from powdered formula tested were susceptible to all antimicrobials agents tested except one isolate which showed intermediate resistance to ciprofloxacin. The prevalence of B. cereus contamination in goat-based powdered formula was higher than that of milk-based powdered formula. A large number of B. cereus isolates (93.0%) carried nhe- and entFM-encoding genes (65.1%). Subtyping results demonstrated that the frequency of nheA, nheB, nheC were 86.1%, 88.4%, 39.5%, while 27.9%, 25.6%, 20.9% were positive for hblA, hblC, hblD, respectively. The cytK gene was detected in 25.6% of B. cereus isolates. There were 5 isolates identified as carrying both hblA/C/D and nheA/B/C and being potentially toxic. These data pointed to the need to improve the hygienic and manufacturing practices during powdered formula production in order to reduce the outbreak burden of foodborne disease risk in China.

Unique biomarkers as a potential predictive tool for differentiation of Bacillus cereus group based on real-time PCR

The aim of the study was to develop unique biomarkers for qPCR detection of Bacillus cereus group. Clinical and soil isolates were identified by specifically designed biomarkers – Lipoprotein (OPL-114-lipo), Methyltransferase (MT-17) and S-layer homology domain protein (151-1BC). In order to design biomarkers, we used 120 bacterial strains grouped into B. cereus and non-Bacillus group. The B. cereus group was confirmed by 108 strains of B. cereus and B. thuringiensis (30 reference and 78 wild), along with 3 strains of B. mycoides, B. pseudomycoides, and B. weihenstephanensis; while the non-Bacillus group was composed of 9 Gram-positive and Gram-negative strains. Direct analysis of samples revealed specificity towards identification and characterization of B. cereus group. The newly developed markers OPL-114-lipo and MT-17 showed specificity of 95% and 81%, respectively in identification of B. cereus. They are efficient tools to identify contaminated sources and the degree of bacterial contamination. Environmental and food samples do not require band isolation, re-amplification, sequencing or sequence identification. Thus, reducing the time and cost of analysis. Hence, it will be an alternative approach to traditional culture methods. Commercial food processing industries will be able to employ these biomarkers specific for B. cereus group as a detection tool to reduce economic loss due to B. cereus contamination.

Prevalence and risk factors for Bacillus cereus in raw milk in Inner Mongolia, Northern China

The prevalence of Bacillus cereus in raw milk from dairy herds in Inner Mongolia and associated risk factors were determined. In total, 160 raw milk samples collected from 2014 to 2015 and examined by culture methods to isolate B. cereus. Fifty‐five samples (34.38%) were positive. The prevalence of B. cereus in raw milk was significantly (P < 0.01) lower in winter (15%) than in summer (50%). The highest prevalence of B. cereus in raw milk was seen in samples collected from small‐ to medium‐sized dairy herds in summer. The results of this study indicated that B. cereus could be a common pathogen in Inner Mongolia because of its high prevalence. It is essential for dairy farmers and producers to strengthen hygienic practices in summer to control B. cereus contamination in raw milk. These results will be useful in establishing proper management procedures to reduce the prevalence of B. cereus in raw milk.