Combined induction of penicillinase in Bacillus cereus by means of various inducers. 3. Penicillinase induction in B. cereus by a single inducer after preincubation with another inducer.
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Emetic toxin-producing Bacillus cereus group species are an important problem, because the staple food for Korean is grains such as rice. In this study, we determined the prevalence (24 of 129 isolates) of emetic B. cereus in 36,745 stool samples from sporadic food-poisoning cases in Korea between 2007 and 2008. The toxin gene profile, toxin production, and biofilm-forming ability of the emetic B. cereus isolates were investigated. Repetitive element sequence polymorphism polymerase chain reaction fingerprints (rep-PCR) were also used to assess the intraspecific biodiversity of these isolates. Emetic B. cereus was present in 0.07% of the sporadic food-poisoning cases. The 24 emetic isolates identified all carried the nheABC and entFM genes and produced NHE enterotoxin. However, they did not have hemolysin BL toxin or related genes. A relationship between biofilm formation and toxin production was not observed in this study. The rep-PCR fingerprints of the B. cereus isolates were not influenced by the presence of toxin genes, or biofilm-forming ability. The rep-PCR assay discriminated emetic B. cereus isolates from nonemetic isolates, even if this assay did not perfectly discriminate these isolates. Further study on emetic isolates possessing a high degree of diversity may be necessary to evaluate the performance of the subtyping assay to discriminate emetic and nonemetic B. cereus isolates and could provide a more accurate indication of the risk from B. cereus strains.
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The ability of certain strains of Bacillus cereus consistently to elaborate a filterable non-dialysable toxin capable of causing severe disruption and necrosis of the intestinal mucosa and submucosa is confirmed. This property is not universal to all B. cereus strains and different degrees of production of this toxin are exhibited by the different strains which produce it. The necrotic effect is produced by whole-cell cultures of the toxin producing strains in broth and in boiled rice. Some characteristics of this necrotic toxin are described and its relationship with the diarrhoeal and other known B. cereus toxins is discussed.
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Enteropathogenic Bacillus cereus causes foodborne infections due to the production of pore-forming enterotoxins in the intestine. Before that, spores have to be ingested, survive the stomach passage, and germinate.
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Β. cereus is a spore-forming bacterium, frequently found in the environment. Most of the strains can grow at a temperature range of 10° - 42° C. B. cereus grows under aerobic conditions, but anaerobic growth is, also, feasible. D1 2 1 values of the spores of B. cereus strains are usually in the range of 0.03 to 2.35 min. The pathogen produces at least five different enterotoxins (HBL, Nhe, CytK, BceT and FM) and one emetic toxin. The enterotoxins HBL, Nhe and CytK are the etiological agents of the B. cereus diarrhoeal disease. The enterotoxins are heat sensitive and can be inactivated by heating at 56° C for 5 min. They are, also, sensitive to low pH and proteolytic activity of enzymes and, subsequently, are inactivated in the acid environment of the stomach.B. cereus emetic toxin has been kept stable even in a heat treatment at 121° C for 2 h in in vitro tests. The emetic toxin is highly resistant to low pH (as low as 2) and to proteolysis. Thus, the emetic toxin cannot be inactivated in the acidic environment of the stomach and the enzyme proteolytic activity in the intestinal tract. B. cereus causes either a diarrhoeal or an emetic type of foodborne disease. The diarrhoeal disease is caused by the B. cereus enterotoxins, which are formed in the intestinal tract after the spores' germination and the subsequent growth of the vegetative cells. The symptoms are watery diarrhoea, abdominal cramps and pain. The emetic disease is caused by the ingestion of the preformed toxins in the foods. The symptoms are nausea and vomiting, occasionally followed by abdominal pain or diarrhoea. Foodborne outbreaks caused by B. cereus have been associated with various foods. The emetic disease has often been associated with the consumption of rice, pasta and other starchy foods, while the diarrheal disease is often linked to the consumption of dairy products, vegetables and meat. The most common food sources for B. cereus infections in humans are milk and dairy products. Among the reported foodborne outbreak cases in North America, Europe and Japan attributed to B. cereus represent a percentage of 1% to 22%. Most B. cereus foodborne cases were associated with the consumption of cooked foods that were cooled slowly and stored under improper refrigeration conditions. Foodborne diseases caused byB. cereus constitute a major problem in restaurants and catering services. Application of control measures, such as Good Manufacturing Practices (GMP) and Hazard Analysis Critical Control Points system (HACCP), in food processing lines can prevent contamination of the foods with pathogens like B. cereus.
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Bacillus cereus sensu stricto (B. cereus) belongs to the B. cereus group, and is a well-known foodborne pathogen causing human disease including emesis which is caused by an emetic toxin, cereulide, with 105-108 cells per gram required to cause disease. The presence of this highly heat, pH and protease-resistant toxin presents a serious challenge to the food industry, as the bacteria itself may be eliminated during processing but the cereulide toxin will survive most food processing techniques. This study shows that cereulide toxin is associated with cells and biofilm structures rather than suspended in the surrounding liquid phase or environment. This is the first report investigating the cereulide toxin production in the presence of biofilms of B. cereus, showing that the cereulide toxin produced is associated with biofilm complex and also attaches to the substrate such as glass and stainless-steel on which the biofilm grows. The RT-qPCR showed that the expression of cesA and cesB were comparable between planktonic cells and biofilms. This study contributes a better understanding of food safety issues in the industry caused by cereulide toxin produced by B. cereus, and provides valuable information for developing control methods for cereulide toxin in the food industry.
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Timing of Enzyme Synthesis During Outgrowth of Spores of Bacillus cereus I. Ordered Enzyme Synthesis
During outgrowth of spores of Bacillus cereus T, the pattern of enzymes synthesized varied with respect to time. The periods of synthesis of α-glucosidase, l -alanine dehydrogenase, and histidase were ordered; each began at a specific time and synthesis continued for only a brief period. An examination of the timing of induced α-glucosidase and induced histidase was made to determine whether specific regions of the genome were continually available for transcription and regulation during this period. Several observations indicated that inducers could function during outgrowth, but for only a limited time interval. The period of induced enzyme synthesis occurred over the same interval as that observed for uninduced and catabolically repressed cultures. When inducer was added partway through the period of gene expression, the level of enzyme induction was diminished. Addition of inducer at a time after the period of gene expression had no significant effect. Since messenger ribonucleic acid formed during outgrowth had a half-life of only a few minutes, it was concluded that ordered enzyme synthesis was a result of ordered transcription of the corresponding portion of the genome. An examination of the timing of induced α-glucosidase and histidase synthesized in the presence of actinomycin D supported this conclusion.
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ABSTRACT Bacillus cereus is ubiquitous in nature, and while most isolates appear to be harmless, some are associated with food-borne illnesses, periodontal diseases, and other more serious infections. In one such infection, B. cereus G9241 was identified as the causative agent of a severe pneumonia in a Louisiana welder in 1994. This isolate was found to harbor most of the B. anthracis virulence plasmid pXO1 (13). Here we report the characterization of two clinical and one environmental B. cereus isolate collected during an investigation of two fatal pneumonia cases in Texas metal workers. Molecular subtyping revealed that the two cases were not caused by the same strain. However, one of the three isolates was indistinguishable from B. cereus G9241. PCR analysis demonstrated that both clinical isolates contained B. anthracis pXO1 toxin genes. One clinical isolate and the environmental isolate collected from that victim's worksite contained the cap A , B , and C genes required for capsule biosynthesis in B. anthracis . Both clinical isolates expressed a capsule; however, neither was composed of poly- d -glutamic acid. Although most B. cereus isolates are not opportunistic pathogens and only a limited number cause food-borne illnesses, these results demonstrate that some B. cereus strains can cause severe and even fatal infections in patients who appear to be otherwise healthy.
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Biofilm formation by 102 Bacillus cereus and B. thuringiensis strains was determined. Strains isolated from soil or involved in digestive tract infections were efficient biofilm formers, whereas strains isolated from other diseases were poor biofilm formers. Cell surface hydrophobicity, the presence of an S layer, and adhesion to epithelial cells were also examined.
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Bacillus cereus is a Gram-positive, pathogenic bacterium capable of causing an ocular infection known as endophthalmitis. The virulence of B. cereus during endophthalmitis is largely attributed to the presence of toxins such as Hbl and Nhe. Although broad-spectrum antibiotics such as vancomycin are able to control B. cereus in the eye during infection, these antibiotics can be toxic to sensitive retinal cells, and they do not control the damaging inflammatory response mounted by the host. Carvacrol is an extract from oregano oil with both antimicrobial and anti-inflammatory qualities that may serve as a possible alternative treatment for B. cereus endophthalmitis. However, at subinhibitory levels, carvacrol increases the virulence of B. cereus. We hypothesize that B. cereus exposed to subinhibitory carvacrol concentrations will cause more damage to the eye than the bacteria alone without progressing into a systemic infection in an in vivo mouse model. Systemic pro-inflammatory cytokines (TNF-α and IL-6) and anti-B. cereus IgG levels were measured by enzyme-linked immunosorbent assays. We found that mice infected with B. cereus and the subinhibitory concentration (SIC) of carvacrol had higher systemic levels of TNF-α, IL-6, and anti-B. cereus IgG. Ocular damage caused by infection with B. cereus was quantified by histological analysis. We found that eyes infected with B. cereus stressed with the SIC of carvacrol had more damage than eyes infected with the bacteria alone. However, ocular damage was not significantly different in mice treated with B. cereus stressed with the SIC of carvacrol and mice treated with the SIC of carvacrol alone. We determined that endophthalmitis caused by B. cereus stressed with the SIC of carvacrol results in an increased systemic immune response and increased ocular damage, but we are unable to confirm if these increases are due to bacterial virulence or irritation caused by carvacrol. Future studies will investigate the effects of carvacrol on retinal pigment epithelial (RPE) cells found in the blood-retinal barrier.
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