Growth and toxin profiles of Bacillus cereus isolated from different food sources

Comparison of enterotoxin production and phenotypic characteristics between emetic and enterotoxic Bacillus cereus

Bacillus cereus was divided into emetic toxin (cereulide)- and enterotoxin-producing strains, but emetic toxin-producing B. cereus is difficult to detect immunochemically. Screening methods for emetic toxin-producing B. cereus are needed. The objectives of this study were to identify and detect emetic toxin-producing B. cereus among 160 B. cereus strains, and to compare enterotoxin production and phenotypic characteristics between the emetic toxin-producing and enterotoxin-producing strains. Forty emetic toxin-producing B. cereus strains were determined with high-pressure liquid chromatography-mass spectrometry analysis. Among the emetic toxin-producing strains (n = 40), 31 (77.5%) and 3 (7.5%) strains produced nonhemolytic enterotoxin (NHE) and hemolysin BL (HBL) enterotoxins, respectively. In addition, 107 (89.2%) and 100 (83.3%) strains produced NHE and HBL enterotoxins among the enterotoxin-producing strains (n = 120). The number of strains positive for starch hydrolysis, salicin fermentation, and hemolysis among the emetic toxin-producing strains were 3 (7.5%), 3 (7.5%), and 26 (65.0%), respectively, and among enterotoxin-producing strains, these numbers were 101 (84.2%), 100 (83.3%), and 111 (92.5%), respectively. In particular, the three emetic toxin-producing B. cereus strains (JNHE 6, JNHE 36, and KNIH 28) produced the HBL and NHE enterotoxins and were capable of starch hydrolysis and salicin fermentation. The absence of HBL enterotoxin and certain phenotypic properties, such as starch hydrolysis and salicin fermentation, indicates that these properties were not critical characteristics of the emetic toxin-producing B. cereus tested in this study.

Biodiversity of psychrotrophic bacteria of the Bacillus cereus group collected on farm and in egg product industry

The aim of the present study was (i) to type, by genotypic and phenotypic methods, a collection of psychrotrophic bacteria belonging to the Bacillus cereus group collected in a farm and in 6 egg breaking industries during a period covering a warm and a cold season, and (ii) to characterize the egg product spoilage (growth in liquid whole egg) and the sanitary risk potential (cytotoxic activity on Caco-2 cells and adhesion on stainless steel) of each isolate of the collection. The investigation of specific psychrotrophic and mesophilic signatures together with the study of ability to grow at 6 °C and/or at 43 °C on optimal agar medium allowed highlighting twelve profiles, the major one corresponding to the species Bacillus weihenstephanensis (46.2% of the collection). The diversity of the profiles depended on the season and on the origin of the isolates. In terms of food spoilage, all the isolates were able to grow at the same level in liquid whole egg and in optimal medium, even at low temperature. Under the same conditions, the cytotoxic activity depended on the isolate, the medium and the temperature. At 10 °C, no isolate was cytotoxic at 10 °C in liquid whole egg and only one, belonging to the Bacillus weihenstephansensis species, in the optimal medium. All the isolates were able to adhere on stainless steel at various levels, from 2.6±0.2 log cfu/cm(2) to 4.9±0.1 log cfu/cm(2). A large majority (80.8%) was strongly adhering and could lead to the formation of biofilms in industrial equipments.

Multiplex PCR assay for the detection of enterotoxic Bacillus cereus group strains and its application in food matrices

Bacillus cereus, Bacillus thuringiensis and Bacillus anthracis are the major concerns for the food safety in terms of frequency and/or seriousness of the disease. Being members of the same group and sharing DNA homology to a larger extent, they do create problems when their specific detection/identification is attempted from different food and environmental sources. Numerous individual polymerase chain reaction (PCR) and few multiplex PCR (mPCR) methods have been employed to detect these organisms by targeting toxin genes but with lack of internal amplification control (IAC). Therefore, we attempted a mPCR with IAC for the detection of enterotoxic B. cereus group strains by selecting hbl A, nhe A and cyt K genes from B. cereus, indicative of the diarrheal potential and cry I A and pag genes, the plasmid borne phenotypic markers specific to B. thuringiensis and B. anthracis strains, respectively. Multiplex PCR assay validation was performed by simultaneous comparison with the results of single-target PCR assays and correlated to the classical conventional and biochemical identification of the organisms. The mPCR was able to detect as low as 10(1)-10(2) organisms per ml following overnight enrichment of spiked food samples (vegetable biriyani and milk) in buffered peptone water (BPW). The presence of these organisms could also be detected by mPCR in naturally contaminated samples of rice based dishes and milk. The high throughput and cost-effective mPCR method described could provide a powerful tool for simultaneous, rapid and reliable detection of enterotoxic B. cereus group organisms.

InhA1, NprA, and HlyII as candidates for markers to differentiate pathogenic from nonpathogenic Bacillus cereus strains

Bacillus cereus is found in food, soil, and plants, and the ability to cause food-borne diseases and opportunistic infection presumably varies among strains. Therefore, measuring harmful toxin production, in addition to the detection of the bacterium itself, may be key for food and hospital safety purposes. All previous studies have focused on the main known virulence factors, cereulide, Hbl, Nhe, and CytK. We examined whether other virulence factors may be specific to pathogenic strains. InhA1, NprA, and HlyII have been described as possibly contributing to B. cereus pathogenicity. We report the prevalence and expression profiles of these three new virulence factor genes among 57 B. cereus strains isolated from various sources, including isolates associated with gastrointestinal and nongastrointestinal diseases. Using PCR, quantitative reverse transcriptase PCR, and virulence in vivo assays, we unraveled these factors as potential markers to differentiate pathogenic from nonpathogenic strains. We show that the hlyII gene is carried only by strains with a pathogenic potential and that the expression levels of inhA1 and nprA are higher in the pathogenic than in the nonpathogenic group of strains studied. These data deliver useful information about the pathogenicity of various B. cereus strains.

Simultaneous detection of pathogenic B. cereus, S. aureus and L. monocytogenes by multiplex PCR

Three important foodborne pathogens, Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus are of major concern for food safety in terms of frequency and seriousness of the disease. The occurrence these three important pathogens and their coexistence in food matrices are predominant. Moreover, symptoms associated with B. cereus and S. aureus food poisoning not only closely resembles each other but can also be overlapping with other foodborne infections. In this context, detection of these three pathogens simultaneously in food samples by a single multiplex PCR (mPCR) would have advantages in terms of rapidity and cost saving, when compared with single organism specific PCRs. mPCR has been standardized by targeting three major diarrheal enterotoxin genes hbl A, cyt K and nhe A of B. cereus, virulence associated nuc and Ent B genes of S. aureus and virulence associated hly and iap genes of L. monocytogenes along with internal amplification control (IAC). The results showed that mPCR accurately identified all the three organisms individually or in combination without non-specificity. The mPCR was able to detect as low as 10 to 100 organisms per ml of growth following overnight enrichment of spiked food samples (vegetable biriyani and milk) and their presence in naturally contaminated samples also. The high throughput and cost effective multiplex PCR method developed in this study could provide a powerful tool for simultaneous, rapid and reliable detection of B. cereus, S. aureus and L. monocytogenes in food samples.

Prevalence, genetic diversity, and antibiotic susceptibility of Bacillus cereus strains isolated from rice and cereals collected in Korea

Incidence and properties of Bacillus cereus strains naturally present in cereals were evaluated by phenotypic characterization, antibiotic susceptibility testing, and pulsed-field gel electrophoresis. Of 293 cereal samples tested, 73 (25%) contained B. cereus strains. Incidence of B. cereus isolates varied with respect to sample; they were found in 15 (37%) of 83 brown rice samples, 23 (37%) of 63 glutinous rice samples, 16 (21%) of 76 barley samples, and 19 (27%) of 71 Job's tears samples. All B. cereus isolates from cereals were positive for diarrheal toxin genes. The isolates were susceptible to most of the antibiotics tested, but they were highly resistant to ampicillin, cefepime, oxacillin, and penicillin. Of the genes assayed by the PCR technique, a high frequency of nheA (99%) and hblDC (84%) was found in the genomic DNA of cereal-associated isolates, whereas cytK was less common (55%). From the strains carrying the hblDC genes, 93% produced enterotoxin HBL. B. cereus isolates did not have significant genetic homology. The genetic diversity and toxic potential differ among the strains isolated from cereals. These results provide important information on toxin gene profiles of cereal-associated B. cereus for population studies.

Survival of Bacillus cereus vegetative cells during Spanish-style fermentation of conservolea green olives

The aim of this research was to investigate the survival of artificially inoculated Bacillus cereus during Spanish-style green olive fermentation. Olives were initially treated with lye and subjected to different fermentation procedures including (i) heat shock (85 degrees C for 10 min) and inoculation with Lactobacillus plantarum ACA-DC 287, (ii) heat shock and inoculation with L. plantarum ACA-DC 146, (iii) heat shock and inoculation with Lactobacillus pentosus isolated during previous studies, and (iv) fermentation by indigenous flora (control process). Microbial growth and survival, pH, titratable acidity, and organic acid evolution were monitored. Inactivation of B. cereus was observed during all processes. The pathogen population declined during all fermentations, but a tailing effect was observed in the brines when the population reached 2 log CFU/ml, at which point the pathogen does not pose a risk to human health. The rate of inactivation was higher in heat-shocked inoculated olives (mean of -2.21 log CFU/day) compared with control olives (-1.26 log/day), indicating an advantage of heat shock and inoculation over spontaneous fermentation. The production of organic acids (primarily lactic acid) during fermentation seemed to be the main factor that determined the behavior of the pathogen under stress conditions prevailing in the brine. Principal components analysis was useful for distinguishing among the different fermentation processes on the basis of the relevant organic acid profile.

The genetically remote pathogenic strain NVH391-98 of the Bacillus cereus group is representative of a cluster of thermophilic strains

Bacteria of the Bacillus cereus group are known to cause food poisoning. A rare phylogenetically remote strain, NVH391-98, was recently characterized to encode a particularly efficient cytotoxin K presumably responsible for food poisoning. This pathogenic strain and its close relatives can be phenotypically distinguished from other strains of the B. cereus group by the inability to grow at temperatures below 17 degrees C and by the ability to grow at temperatures from 48 to 53 degrees C. A temperate phage, phBC391A2, residing in the genome of NVH391-98 allows us to distinguish the three known members of this thermophilic strain cluster.

Isolation and characterization of a psychrotolerant toxin producer, Bacillus weihenstephanensis, in liquid egg products

A psychrotolerant bacteria of the Bacillus cereus group was found responsible for the spoilage of whole liquid egg products. By sequencing a 16S rRNA region and performing a PCR amplification of specific 16S rRNA and cspA signatures, a Bacillus weihenstephanensis was identified. Characterization of this strain shows its ability to grow in defined medium as well as in whole liquid egg at refrigerated temperatures. The strain isolated possesses genes encoding for hemolysin BL, nonhemolytic enterotoxin, and B. cereus enterotoxins and produces enterotoxins with cytotoxic activity in whole liquid egg, even at refrigerated temperatures. The isolate exhibits a clear ability to stick and form biofilms on stainless steel, the most common material used in egg breaking factories, as well as on model hydrophilic (glass) and hydrophobic (polytetrafluoroethylene) materials. These findings show the necessity to monitor for Bacillus contamination in egg products that are often used in the composition of particularly susceptible finished products such as cream, dessert, dairy, meat, and seafood.

Genetic distribution of 295 Bacillus cereus group members based on adk-screening in combination with MLST (Multilocus Sequence Typing) used for validating a primer targeting a chromosomal locus in B. anthracis

The genetic distribution of 295 Bacillus cereus group members has been investigated by using a modified Multilocus Sequence Typing method (MLST). By comparing the nucleic acid sequence of the adk gene fragment, isolates of B. cereus group members most related to B. anthracis may be easily identified. The genetic distribution, with focus on the B. anthracis close neighbours, was used to evaluate a new primer set for specific identification of B. anthracis. This primer set, BA5510-1/2, targeted the putative B. anthracis specific gene BA5510. Real-time PCR using BA5510-1/2 amplified the target fragment from all B. anthracis strains tested and only two (of 289) non-B. anthracis strains analysed. This is one of the most thoroughly validated chromosomal B. anthracis markers for real-time PCR identification, in which the screened collection contained several very closely related B. anthracis strains.

Germination of Bacillus cereus spores adhered to stainless steel

Adhered spores of Bacillus cereus represent a significant part of the surface-derived contamination in processing equipment used in the dairy industry. As germinated spores lose their resistance capacities instantaneously, efficient germination prior to a cleaning in place treatment could aid to the disinfecting effect of such a treatment. Therefore, spores of B. cereus ATCC 14579 and that of the environmental isolate B. cereus CMCC 3328 were assessed for their germination behaviour when adhered to a stainless steel surface. A mixture of l-alanine and inosine initiated germination of adhered spores efficiently, resulting in 3.2 decimal logarithms of germination. Notably, implementation of a germination-inducing step prior to a representative cleaning in place procedure reduced the number of survivors with over 3 decimal log units, while an alkali treatment alone, as part of the cleaning in place procedure, did not show any effect on B. cereus spore viability. These results show that implementation of a germination step enhances the disinfection effect of currently used cleaning in place procedures.

Presence and significance of Bacillus cereus in dehydrated potato products

Dehydrated potato contains Bacillus cereus at a prevalences of 10 to 40% and at numbers usually less than 10(3) CFU g(-1). B. cereus in dehydrated potato is likely to be present as spores that are able to survive drying of the raw vegetable and may represent a significant inoculum in the reconstituted (rehydrated) product where conditions favor germination of, and outgrowth from, spores. Holding rehydrated mashed potato alone, or as part of another product (e.g., potato-topped pie), at temperatures above 10 degrees C and below 60 degrees C may allow growth of vegetative B. cereus. Levels exceeding 10(4) CFU g(-1) are considered hazardous to human health and may be reached within a few hours if stored inappropriately between these temperatures. Foods incorporating mashed potato prepared from dehydrated potato flakes have been implicated in B. cereus foodborne illness. This review is a summary of the information available concerning the prevalence and numbers of B. cereus in dehydrated potato flakes and the rate at which growth might occur in the rehydrated product.

Prevalence of potentially pathogenic Bacillus cereus in food commodities in The Netherlands

Randomly selected food commodities, categorized in product groups, were investigated for the presence and number of Bacillus cereus bacteria. If positive, and when possible, five separate colonies were isolated and investigated for the presence of four virulence factors: presence of genes encoding three enterotoxins (hemolysin BL [HBL], nonhemolytic enterotoxin [NHE], and cytotoxin K) and the ability to produce cereulide. In addition, the presence of psychrotrophic and mesophilic signatures was determined. The genes for NHE are found in more than 97% of the isolates, those for HBL in approximately 66% of the isolates, and the gene for cytotoxin K in nearly 50% of the isolates. Significant associations between product groups and (combinations of) virulence factors were the relatively low percentage of isolates from the "flavorings" group containing genes encoding NHE and the higher-than-average occurrence of both the genes encoding HBL and NHE in the "pastry" group. Cereulide was produced by 8.2% of the isolates but only in combination with the presence of genes for one or more other virulence factors. Most isolates (89.9%) were mesophilic; minorities of the isolates were psychrotrophic (4.4%) or of intermediate signature (5.7%). In the product group "milk and milk products," the incidence of strains with psychrotrophic or intermediate signatures is significantly higher than in the other product groups. In the product groups "flavorings," "milk and milk products," "vegetable(s) and vegetable products," "pastry," and "ready-to-eat foods," a relatively high number of samples contain high numbers of B. cereus bacteria. Within the product group "ready-to-eat foods," the products containing rice and pasta show a relatively high incidence of high numbers of B. cereus bacteria.

Production of antimicrobial metabolites by strains of Lactobacillus or Lactococcus co-cultured with Bacillus cereus in milk

During co-culture of Lactobacillus (five strains) or Lactococcus (two strains) with Bacillus cereus, organic acids and other potentially antimicrobial metabolites are produced. Lactic acid was produced at very different rates by the lactic acid bacteria (LAB) and the final concentrations varied much, however, the crucial point of rapid pH reduction during the initial hours of fermentation coincides with lactic acid production. Moderate amounts of acetic acid were produced during fermentation and the final concentrations were much smaller compared to lactic acid. According to these experiments, production of diacetyl, carbon dioxide and ethanol was considered too small to contribute to inhibition of B. cereus. The inhibitory substance produced by the LAB strains was not sensitive to proteinase K, trypsin or pepsin, so it was not likely that the LAB strains produced bacteriocins antagonistic against B. cereus. The strains that produced lactic acid fastest inhibited B. cereus best. Increased concentrations of lactic and acetic acid and carbon dioxide were also observed after co-culture with B. cereus compared to growth of the LAB strains alone, which indicates that B. cereus stimulates the biosynthetic capacities of the LAB strains.

Isolation, characterization, and identification of bacterial contaminants in semifinal gelatin extracts

Bacterial contamination of gelatin is of great concern. Indeed, this animal colloid has many industrial applications, mainly in food and pharmaceutical products. In a previous study (E. De Clerck and P. De Vos, Syst. Appl. Microbiol. 25:611-618), contamination of a gelatin production process with a variety of gram-positive and gram-negative bacteria was demonstrated. In this study, bacterial contamination of semifinal gelatin extracts from several production plants was examined. Since these extracts are subjected to harsh conditions during production and a final ultrahigh-temperature treatment, the bacterial load at this stage is expected to be greatly reduced. In total, 1,129 isolates were obtained from a total of 73 gelatin batches originating from six different production plants. Each of these batches was suspected of having bacterial contamination based on quality control testing at the production plant from which it originated. For characterization and identification of the 1,129 bacterial isolates, repetitive-element PCR was used to obtain manageable groups. Representative strains were identified by means of 16S rRNA gene sequencing, species-specific gyrB PCR, and gyrA and rpoB sequencing and were tested for gelatinase activity. The majority of isolates belonged to members of Bacillus or related endospore-forming genera. Representative strains were identified as Bacillus cereus, Bacillus coagulans, Bacillus fumarioli, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus pumilus, Bacillus sonorensis, Bacillus subtilis, Bacillus gelatini, Bacillus thermoamylovorans, Anoxybacillus contaminans, Anoxybacillus flavithermus, Brevibacillus agri, Brevibacillus borstelensis, and Geobacillus stearothermophilus. The majority of these species include strains exhibiting gelatinase activity. Moreover, some of these species have known pathogenic properties. These findings are of great concern with regard to the safety and quality of gelatin and its applications.

Detection of Bacillus cereus on selected retail chicken products

Samples from five chicken meat products, obtained at retail stores, were evaluated for the presence of Bacillus cereus. The products tested were as follows: breaded, fully cooked, frozen nuggets (NUGGETS); breaded, fully cooked, frozen tenders (TENDERS); fully cooked, frozen, white-meat fajita-style strips (STRIPS); raw, refrigerated, boneless, skinless, marinated breast fillets (FILLETS); and raw, refrigerated, cut-up, tray-pack bone-in parts (PARTS), either split breasts or thighs. Four packages of each item were obtained on three different days (n = 60). Frozen and refrigerated products were held overnight in their respective environments as appropriate; then packages were opened aseptically, and a total of 25 g of tissue was excised from multiple pieces within a package. The 25-g samples were enriched in 225 ml of Trypticase soy-polymixin broth for 18 to 24 h at 30 degrees C and then plated on mannitol-egg yolk-polymixin agar and incubated for 18 to 24 h at 30 degrees C. Colonies characteristic of B. cereus were chosen and replated for isolation on mannitol-egg yolk-polymixin agar. Suspect colonies were confirmed as Bacillus spp. by Gram stain, hemolysis on blood agar, and a biochemical test strip. Isolates were further confirmed as B. cereus using Bacteriological Analytical Manual procedures, including tests for motility, rhizoid growth, hemolysis, and protein toxin crystal production. B. cereus was detected in 27 of 60 total samples. By product, the prevalence levels were as follows: NUGGETS, 11 of 12 positive; TENDERS, 8 of 12 positive; STRIPS, 6 of 12 positive; FILLETS, 0 of 12 positive; and PARTS, 2 of 12 positive. Isolates were tested by PCR for presence of the toxin-encoding genes bceT, nheABC, hblACD, and cytK. Results indicate that B. cereus organisms were present on four of the five retail poultry products tested in this study, with the highest rates reported for the three fully cooked items, especially the two breaded products. All strains isolated contained the gene(s) for at least one of the toxins, although none of the strains contained the cytK gene.

Identification of pathogenic microbial cells and spores by electrochemical detection on a biochip

BACKGROUND: Bacillus cereus constitutes a significant cause of acute food poisoning in humans. Despite the recent development of different detection methods, new effective control measures and better diagnostic tools are required for quick and reliable detection of pathogenic micro-organisms. Thus, the objective of this study was to determine a simple method for rapid identification of enterotoxic Bacillus strains. Here, a special attention is given to an electrochemical biosensor since it meets the requirements of minimal size, lower costs and decreased power consumption. RESULTS: A bead-based sandwich hybridization system was employed in conjugation with electric chips for detection of vegetative cells and spores of Bacillus strains based on their toxin-encoding genes. The system consists of a silicon chip based potentiometric cell, and utilizes paramagnetic beads as solid carriers of the DNA probes. The specific signals from 20 amol of bacterial cell or spore DNA were achieved in less than 4 h. The method was also successful when applied directly to unpurified spore and cell extract samples. The assay for the haemolytic enterotoxin genes resulted in reproducible signals from B. cereus and B. thuringiensis while haemolysin-negative B. subtilis strain did not yield any signal. CONCLUSIONS: The sensitivity, convenience and specificity of the system have shown its potential. In this respect an electrochemical detection on a chip enabling a fast characterization and monitoring of pathogens in food is of interest. This system can offer a contribution in the rapid identification of bacteria based on the presence of specific genes without preceding nucleic acid amplification.