Production of diarrheal enterotoxins and other potential virulence factors by veterinary isolates of bacillus species associated with nongastrointestinal infections

Toxigenic diversity of Bacillus cereus isolated from fresh produce and effects of various factors on the growth and the cytotoxicity of B. cereus

This study analyzed the virulence, growth characteristics, and cytotoxicity of Bacillus cereus strains isolated from fresh produce, including romaine lettuce, sesame leaf, tomato, and cucumber grown by different methods. Polymerase chain reaction (PCR) was used to assess the toxigenic potential, and the cytotoxicity of B. cereus was estimated using cell-free supernatant in HEp-2 cells. The study found that hblD was the predominant diarrheal enterotoxin in the 59 isolated B. cereus strains, followed by nheB and hblC. The optimal temperatures for growth ranged from 42 to 44 °C, with the highest growth rates and shortest lag times. Cytotoxicity varied greatly depending on abiotic factors, including NaCl, pH, and medium, and was not always correlated with cell population. The study highlights the importance of establishing control measures to prevent B. cereus intoxication in fresh vegetables.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01330-0.

A buffalo rumen-derived probiotic (SN-6) could effectively increase simmental growth performance by regulating fecal microbiota and metabolism

Microorganisms play a key role in ruminal digestion, some of which can be used as probiotics to promote growth in ruminants. However, which potential bacteria are responsible for ruminant growth and how they potentiate the basic mechanism is unclear. In this study, three bacterial strains, Bacillus pumilus (SN-3), Bacillus paralicheniformis (SN-6), and Bacillus altitudinis (SN-20) with multiple digestive enzymes were isolated from the rumen of healthy buffaloes. Among these strains, SN-6 secreted cellulase, laccase, and amylase, and significantly inhibited Staphylococcus aureus ATCC25923 and Escherichia coli K99 in vitro. In addition, SN-6 exhibited strong tolerance to artificial gastric juice, intestinal juice, and high temperature. Antibiotic resistance test, virulence gene test, and mouse toxicity test confirmed the safety of SN-6. Further, SN-6 significantly increased the body weight (p < 0.01), affects the intestinal microbiota structure, and alters the metabolomic patterns of Simmental. There was a remarkable difference in the β diversity of fecal microflora between SN-6 and control groups (p < 0.05). Furthermore, SN-6 significantly increased the abundance of Clostridium_sensu_stricto_1, Bifidobacterium, Blautia, and Cellulolyticum, decreased the relative abundance of Monoglobus and norank_f_Ruminococcacea. Moreover, SN-6 feeding significantly enriched intestinal metabolites (i.e., 3-indoleacrylic acid, kynurenic acid) to maintain intestinal homeostasis. Finally, the microbial and metabolic functional analysis indicated that SN-6 could enhance amino acid metabolism (mainly tryptophan metabolism) and lipid metabolism pathways. Overall, these findings indicated that SN-6 could be used as a probiotic in ruminants.

National Safety Survey of Animal-use Commercial Probiotics and Their Spillover Effects From Farm to Humans: An Emerging Threat to Public Health

BACKGROUND

Human-use probiotics have recently been associated with clinical infections and antibiotic resistance transfer, raising public concern over their safety. However, despite their extensive application in aquaculture and animal husbandry, the safety of animal-use probiotics remains poorly described.

METHODS

We evaluated the safety of 92 animal-use probiotics from China. The pattern of spread of pathogens from probiotics and the consequent public health implications were also examined by conducting in-field genomic surveillance at 2 farms.

RESULTS

A total of 123 probiotic Bacillus species isolates were obtained from 92 brands of probiotics, of which 45 isolates were resistant to antibiotics. Notably, 33.7% of probiotic products were contaminated with life-threatening pathogens such as Klebsiella pneumoniae. Genomic surveillance at a chicken farm identified an anthrax toxin-positive Bacillus cereus strain in a probiotic product used as a feed supplement, which was transferred into the groundwater and to a nearby fish farm. Following up retrospective analysis of the surveillance data during 2015-2018 in 3 provinces retrieved 2 B. cereus strains from human with intestinal anthrax symptoms and confirmed the transmission of B. cereus from farm to human. Surveillance of anthrax toxin revealed that cya was detected in 8 of 31 farms.

CONCLUSIONS

This study provides the first national safety survey of animal-use probiotics in China and confirms the spillover effects of probiotics from the farms to human. These results suggest that the large-scale application of pathogen-containing probiotics leads to the transfer of pathogens, with worrisome implications for public health. Good Manufacturing Practice should be implemented during the production of all probiotics.Animal-use probiotic products are frequently contaminated with viable pathogenic bacteria. This study revealed that virulent probiotic organisms and contaminating pathogens were colonized with farm animals and shed into the environment, which facilitated the transfer of pathogens to humans.

Safety and Stability Assessment of Potential Probiotic Strains from Fermented Mango Brine Pickle

Fermented foods are known to be rich source of valuable nutrients and probiotics. Previously, our study reported the isolation and characterization of eight potential probiotic strains from traditional mango brine pickle, which has been conventionally consumed for ages in raw form in Southern India. The present study reports on the safety assessment of these strains for the selection of prospective probiotic candidates. Hydrogen peroxide production, histidine decarboxylase activity (production of histamine), DNase activity, and presence of the virulence factor genes (assessed by PCR) were carried out to evaluate its safety. Bacillus licheniformis KT921419 and B. methylotrophicus KT921422 was found to show no adverse safety characteristics. These two strains were further assessed for their ability to survive in the native substrate (mango brine pickle) as single and mixed inoculums. Above strains maintained significant viability in mango brine pickle for a period of 6 months during storage at the room temperature. Results clearly proved the safety and stability of two of the potential probiotic strains, which can be further utilized in food applications under harsh conditions of high salt, low pH, and room temperature making these strains unique.

Goat Colostrum—Source of Toxigenic Bacillus Cereus

The aim of this study was to evaluate the toxigenic potential of Bacillus cereus strains isolated from frozen goat colostrum. Of the 50 phenotypically suspected B. cereus isolates, 39 (78.0 %) were confirmed as B. cereus by the polymerase chain reaction (PCR) method based on the gyrB gene detection. In these isolates, genes encoding the production of haemolysin BL (Hbl), a complex of non-haemolytic enterotoxins (Nhe) and emetic toxin were detected by the PCR method. In 36 (92.3 %) confirmed B. cereus isolates, genes encoding at least one type of toxins of interest were detected. In all toxigenic isolates, we found the presence of genes for Nhe production, and in 16 (41.0 %) of the isolates, genes encoding both Nhe and haemolysin BL were shown. Eight (20.5 %) of the emetic strains of B. cereus were identified. The emetic toxin production gene was always detected simultaneously with genes encoding non-haemolytic enterotoxin production. The ability to produce BL haemolysin and non-haemolytic enterotoxins were confirmed by the immunochromatographic method. In summary, goat colostrum can be a significant source of toxigenic strains of B. cereus.

Isolation and characterization of the Bacillus cereus BC7 strain, which is capable of zearalenone removal and intestinal flora modulation in mice

Zearalenone (ZEN) causes serious diseases in both animals and humans and thereby leads to substantial economic losses. The elimination of ZEN contamination from food and feed is an important concern worldwide. This study aimed to screen a bacterium that can efficiently detoxify ZEN both in vitro and in vivo. A bacterium (designated BC7) with high ZEN-removing capability was isolated from mouldy contaminated feeds and characterized as Bacillus cereus based on biochemical and 16S rRNA sequencing analyses. BC7 could remove 100% and 89.31% of 10 mg/L ZEN in Luria-Bertani (LB) medium and simulated gastric fluid (GSF), respectively, within 24 h at 37 °C. The effects of BC7 on ZEN detoxification and on the intestinal flora were further evaluated using four groups of mice that were intragastrically administered normal saline, BC7 culture (CFU = 3.45 × 10⁸/mL), ZEN (10 mg/kg BW) or BC7 culture (CFU = 3.45 × 10⁸/mL) + ZEN (10 mg/kg BW) for 2 weeks. ZEN showed distinct reproductive and hepatic toxicity, as characterized by increased weights of the uterus and liver, altered levels of oestradiol (E2) and luteinizing hormone (LH), increased secretion of the liver injury biomarkers alanine transaminase (ALT) and aspartate transaminase (AST), and abnormal histological phenotypes for the uterus, ovary and liver. However, BC7 could significantly reduce all the above-mentioned adverse effects caused by ZEN with no harmful effect on the reproductive system and liver in mice. Moreover, the addition of BC7 could efficiently renormalize the ZEN-induced perturbation of the gut microbiota and significantly increase the abundance of Lactobacillus to maintain the health of the intestinal flora in mice. In conclusion, Bacillus cereus BC7 could be used as a potential feed additive to efficiently remove ZEN in vitro or in vivo and to normalize the disordered gut microbiota in mice.

How to select a probiotic? A review and update of methods and criteria

International competition within the dairy market and increasing public awareness about the importance of functional food consumption are providing new challenges for innovation in the probiotic sector. In this context, countless references are currently dedicated to the selection and characterization of new species and more specific strains of probiotic bacteria. In general, these studies adopt basic selection criteria established by the World Health Organization (WHO), including host-associated stress resistance, epithelium adhesion ability, and antimicrobial activity. These aspects are applied to ensure that the candidate probiotic could withstand the stressful conditions of the human digestive system and exert functional proprieties. However, it cannot be assumed that these novel microbial strains are capable of offering several biological benefits attributed to probiotics. Additionally, safety-associated selection criteria, such as plasmid-associated antibiotic resistance spreading and enterotoxin production, are often neglected. This article reviews the recent developments in the processes, strategies, and methods, such as anticarcinogenic, antidepression, antianxiety, antiobesity, antidiabetic, immunostimulatory, and cholesterol-lowering assessments, to select probiotic strains with the ultimate objective of assisting future probiotic microbe evaluation studies.

Microbial survey of ready-to-eat salad ingredients sold at retail reveals the occurrence and the persistence of Listeria monocytogenes Sequence Types 2 and 87 in pre-packed smoked salmon

BACKGROUND

As the preparation of salads involves extensive handling and the use of uncooked ingredients, they are particularly vulnerable to microbial contamination. This study aimed to determine the microbial safety and quality of pre-packed salads and salad bar ingredients sold in Singapore, so as to identify public health risks that could arise from consuming salads and to determine areas for improvement in the management of food safety.

RESULTS

The most frequently encountered organism in pre-packed salad samples was B. cereus, particularly in pasta salads (33.3%, 10/30). The most commonly detected organism in salad bar ingredients was L. monocytogenes, in particular seafood ingredients (44.1%, 15/34), largely due to contaminated smoked salmon. Further investigation showed that 21.6% (37/171) of the pre-packed smoked salmon sold in supermarkets contained L. monocytogenes. Significantly higher prevalence of L. monocytogenes and higher Standard Plate Count were detected in smoked salmon at salad bars compared to pre-packed smoked salmon in supermarkets, which suggested multiplication of the organism as the products move down the supply chain. Further molecular analysis revealed that L. monocytogenes Sequence Type (ST) 2 and ST87 were present in a particular brand of pre-packed salmon products over a 4-year period, implying a potential persistent contamination problem at the manufacturing level.

CONCLUSIONS

Our findings highlighted a need to improve manufacturing and retail hygiene processes as well as to educate vulnerable populations to avoid consuming food prone to L. monocytogenes contamination.

Probiotic Activity of a Bacterial Strain Isolated from Ancient Permafrost Against Salmonella Infection in Mice

Bacillus cereus strain F, collected from relict permafrost located in Siberia, was analyzed for probiotic activity in the mouse Salmonella enterica model. Viable bacterial cells were found in frozen soils taken at Mammoth Mountain in Yakutia from a depth below the level of seasonal thawing. Geological data indicated the absence of a thawing within millions of years of deposited soils, which helped to ensure the ancient origin of our sample. According to DNA analysis, bacterial cells collected from the relict permafrost appeared to be B. cereus strain F. The morphology of these bacteria was analyzed using atomic force microscopy. B. cereus strain F was assessed as a nonpathogenic bacterium by evaluation of its pathogenicity. A S. enterica model is described in mice after per oral inoculation and serves as a model for the human carrier state. Using this model, probiotic activity by the bacterial strain isolated from the ancient permafrost has been shown against Salmonella infection in mice.

Characteristics of enterotoxin distribution, hemolysis, lecithinase, and starch hydrolysis of Bacillus cereus isolated from infant formulas and ready-to-eat foods

Bacillus cereus is a ubiquitous environmental microbe implicated as a main cause of food poisoning with various symptoms, depending on the strain type and the isolation source. In this study, the potential virulence factors and biochemical properties of B. cereus isolated from infant formulas and ready-to-eat (RTE) foods were analyzed and compared. A total of 347 B. cereus strains were isolated and identified from 687 infant food formulas and RTE food samples. All the isolates had one or more enterotoxin genes, and one-half of the strains had all 3 enterotoxin genes (hbl, nhe, and cytK) that are involved in food poisoning in humans. Here, all the 3 genes were detected in 50% of the B. cereus isolates from RTE foods and only 14% of the isolates were identified from infant formulas. The latter harbored low cytK and bceT, and very low hbl genes. Most B. cereus isolates possessed the hemolysis gene, but not the ces gene. The infant formula isolates showed stronger hemolysis activity than the other isolates. In addition, 26% of the total isolates showed low lecithinase activities and 10% showed high lecithinase activities. A greater number of isolates from the infant formula showed high lecithinase activity than those from the RTE foods. Approximately 83% of the isolates were positive and 17% were negative for starch hydrolysis. Over 90% of the RTE food isolates and only 35% of the infant formula isolates were positive for starch hydrolysis. However, all the strains possessed nhe, but their harboring patterns of hbl and cytK were significantly different. Most starch-hydrolyzing strains possessed hbl, but only 23% nonstarch-hydrolyzing isolates possessed this gene. Moreover, very low nonstarch hydrolyzing strains harbored cytK. Most nonstarch-hydrolyzing isolates showed high lecithinase and strong hemolysis activities, and very low hbl and cytK harboring. In summary, most infant formula isolates showed stronger hemolysis and higher lecithinase activities with lower frequency of harboring hbl and cytK and lower starch hydrolysis compared with RTE food isolates.

The genetic diversity of cereulide biosynthesis gene cluster indicates a composite transposon Tnces in emetic Bacillus weihenstephanensis

Background

Cereulide is a cyclic dodecadepsipeptide ionophore, produced via non-ribosomal peptide synthetases (NRPS), which in rare cases can lead to human death. Early studies had shown that emetic toxin formation belongs to a homogeneous group of Bacillus cereus sensu stricto and the genetic determinants of cereulide (a 24-kb gene cluster of cesHPTABCD) are located on a 270-kb plasmid related to the Bacillus anthracis virulence plasmid pXO1.

Results

The whole genome sequences from seven emetic isolates, including two B. cereus sensu stricto and five Bacillus weihenstephanensis strains, were compared, and their inside and adjacent DNA sequences of the cereulide biosynthesis gene clusters were analyzed. The sequence diversity was observed, which classified the seven emetic isolates into three clades. Different genomic locations of the cereulide biosynthesis gene clusters, plasmid-borne and chromosome-borne, were also found. Potential mobile genetic elements (MGEs) were identified in the flanking sequences of the ces gene cluster in all three types. The most striking observation was the identification of a putative composite transposon, Tnces, consisting of two copies of ISces element (belonging to IS6 family) in opposite orientations flanking the ces gene cluster in emetic B. weihenstephanensis. The mobility of this element was tested by replacing the ces gene cluster by a Km^R gene marker and performing mating-out transposition assays in Escherichia coli. The results showed that Tnces::km transposes efficiently (1.04 × 10^-3 T/R) and produces 8-bp direct repeat (DR) at the insertion sites.

Conclusions

Cereulide biosynthesis gene clusters display sequence diversity, different genomic locations and association with MGEs, in which the transposition capacity of a resistant derivative of the composite transposon Tnces in E. coli was demonstrated. Further study is needed to look for appropriate genetic tools to analysis the transposition of Tnces in Bacillus spp. and the dynamics of other MGEs flanking the ces gene clusters.

Public health implications of contamination of Franc CFA (XAF) circulating in Buea (Cameroon) with drug resistant pathogens

Background

Studies in different parts of the world have implicated money as a vehicle for transmission of pathogens. Such information which is necessary to facilitate infection control strategies is lacking in many sub-Saharan countries including Cameroon. This study analyzed the Franc de la Communauté Financiere d’Afrique (Franc CFA), the currency used in Cameroon and other countries in the Central African sub-region, as a potential vehicle for transmission of pathogenic bacteria and fungi, particularly drug-resistant strains, to generate findings which could create awareness on currency contamination and serve as a guide when formulating health policies on currency.

Methods

Two hundred and thirteen currency samples representing various denominations of notes and coins randomly collected from diverse sources in Buea, Cameroon were analyzed for bacteria and fungi. The sensitivity of bacterial isolates to antibiotics was tested using the disc diffusion method. The relationship between contamination and physical state, source or denomination of currency was assessed using the χ² test. All statistics were discussed at 0.05 significance level.

Results

Two hundred (93.9%) samples were contaminated with notes (96.6%) showing higher contamination than coins (88.2%). Uncirculated (mint) samples showed no contamination. There was a significant difference (P˂0.05) in contamination with respect to currency denomination, physical state and source. All samples from butchers and patients/personnel in hospitals were contaminated. Lower denominations showed significantly higher (P = 0.008) levels of contamination than higher denominations. Dirty currency was more contaminated than clean currency. Nine bacterial species were isolated. Coagulase-negative Staphylococcus (CoNS) (54.9%) and Staphylococcus aureus (20.1%) predominated. Among the fungi detected, Aspergillus sp (17.3%) and Penicillium sp (15.9%) showed higher frequency of occurrence. Bacteria were susceptible (100%) to ceftriaxone, gentamicin, norfloxacin and ofloxacin. Susceptibility to amoxicillin, penicillin, ampicillin, vancomycin and cotrimoxazole was low. Staphylococci were resistant (100%) to vancomycin, penicillin G, and amoxicillin. CoNS in addition showed resistance (100%) to cotrimoxazole.

Conclusions

The CFA franc circulating in Buea could serve as a vehicle for transmission of drug resistant pathogenic or potential organisms and contamination could be due to currency usage and handling as mint notes were not contaminated. Hygiene practices during or after handling currency is greatly encouraged to prevent infection.

Biotoxin detection using cell-based sensors

Cell-based biosensors (CBBs) utilize the principles of cell-based assays (CBAs) by employing living cells for detection of different analytes from environment, food, clinical, or other sources. For toxin detection, CBBs are emerging as unique alternatives to other analytical methods. The main advantage of using CBBs for probing biotoxins and toxic agents is that CBBs respond to the toxic exposures in the manner related to actual physiologic responses of the vulnerable subjects. The results obtained from CBBs are based on the toxin-cell interactions, and therefore, reveal functional information (such as mode of action, toxic potency, bioavailability, target tissue or organ, etc.) about the toxin. CBBs incorporate both prokaryotic (bacteria) and eukaryotic (yeast, invertebrate and vertebrate) cells. To create CBB devices, living cells are directly integrated onto the biosensor platform. The sensors report the cellular responses upon exposures to toxins and the resulting cellular signals are transduced by secondary transducers generating optical or electrical signals outputs followed by appropriate read-outs. Examples of the layout and operation of cellular biosensors for detection of selected biotoxins are summarized.

Safety assessment of Bacillus licheniformis Me1 isolated from milk for probiotic application

In this study, an in vivo toxicological safety assessment of Bacillus licheniformis Me1, a native isolate from milk, was performed. An acute toxicity study in male albino Wistar rats demonstrated no treatment-related illness or mortality. A 90-day subchronic oral toxicity study using 2 doses (1.1 × 10(10) and 1.1 × 10(11) colony-forming unit [CFU]/kg body weight [BW], respectively) failed to show dose-dependent illness or mortality. Moreover, neither significant differences in serum biochemical and hematological analyses nor histopathological changes in organs or tissues were found when compared to the control groups. The no-observed-adverse-effect level (NOAEL) was found to be greater than 1.1 × 10(11) CFU/kg BW. The in vivo micronucleus assay in mice did not reveal any signs of genotoxic effect at any of the doses tested. Furthermore, dermal and acute eye irritation tests conducted in rabbits showed no edema or erythema and ocular lesions. These results suggest that B licheniformis Me1 can be considered safe for food industry applications.

Phenotypic & genetic characterization of Bacillus cereus isolated from the acute diarrhoeal patients

BACKGROUND & OBJECTIVES

Bacillus cereus is one of the pathogens responsible for human diarrhoea, mainly due to consumption of contaminated food. The present study was undertaken to determine the occurrence of B. cereus among diarrhoeal patients and its phenotypic and genetic characteristics that determine the virulence and clonal features.

METHODS

Stool specimens were collected for two years from acute diarrhoeal patients attending the two referral hospitals in Kolkata. Presence of virulence genes in B. cereus was determined by PCR. Clonality was assessed by pulsed-field gel analysis (PFGE) by restriction digestion with SmaI and NotI enzymes. Enterotoxins were detected by haemolysin assay and using BCET-RPLA kit. Invasion assay was done on Hep-2 cell line. Antimicrobial susceptibility was tested by disc diffusion method.

RESULTS

B. cereus was identified in 54 (3.5%) of the 1536 diarrhoeal cases studied. Majority of the isolates were susceptible to many antibiotics but showed resistant to amoxyclav and cephalosporins. Six genes covering the two different enterotoxic complexes determining the pathogenicity of B. cereus have been characterized by PCR. The nhe genes were detected in a higher proportion than hbl. Except in two, clonal diversity was noticed among 21 B. cereus isolates. Haemolytic enterotoxin was detected in 76 per cent of the isolates. Majority of the isolates (67%) produced in vitro enterotoxin (BCET) confirming its involvement in the infection.

INTERPRETATION & CONCLUSIONS

Though the presence of B. cereus was not high in patients with diarrhoea, several virulence factors confirm their association with diarrhoea. Distinct clonality was identified in majority of the isolates indicating their origin from different sources.

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.

Preclinical testing in the development of probiotics: a regulatory perspective with Bacillus strains as an example

Preclinical testing of the microbial strains is the first important step in the development of probiotics. Requirements for the set of tests can vary depending on the bacterial species and the expected mechanism of action in the organism. Common approaches to preclinical testing of probiotic strains include strain identification (i.e., determination of phenotypic and genotypic properties), safety evaluation (i.e., characterization of history of use [safety contact], assessment of resistance to antibiotics, and evaluation of pathogenic properties in vitro and in animal models), and efficacy testing (i.e., functional characterization). Future progress in probiotics requires more studies to determine the mechanisms of their action, as well as an understanding of the basis and mechanisms of pathogenicity for different probiotic strains. Special attention should be given to recombinant probiotics, particularly in the formulation of criteria for selection of the host strain, for assessment of environmental safety, and for tracing the fate of recombinant DNA in vitro and in vivo.

The safety of two Bacillus probiotic strains for human use

Probiotics based on Bacillus strains have been increasingly proposed for prophylactic and therapeutic use against several gastro-intestinal diseases. We studied safety for two Bacillus strains included in a popular East European probiotic. Bacillus subtilis strain that was sensitive to all antibiotics listed by the European Food Safety Authority. Bacillus licheniformis strain was resistant to chloramphenicol and clindamycin. Both were non-hemolytic and did not produce Hbl or Nhe enterotoxins. No bceT and cytK toxin genes were found. Study of acute toxicity in BALB/c mice demonstrated no treatment-related deaths. The oral LD(50) for both strains was more than 2 x 10(11) CFU. Chronic toxicity studies were performed on mice, rabbits, and pigs and showed no signs of toxicity or histological changes in either organs or tissues. We demonstrated that while certain risks may exist for the B. licheniformis strain considering antibiotic resistance, B. subtilis strain may be considered as non-pathogenic and safe for human consumption.

Efficacy of enterocin AS-48 against bacilli in ready-to-eat vegetable soups and purees

The broad-spectrum bacteriocin enterocin AS-48 was tested for biopreservation of ready-to-eat vegetable foods (soups and purees) against aerobic mesophilic endospore-forming bacteria. By adding AS-48 (10 microg/ml), Bacillus cereus LWL1 was completely inhibited in all six vegetable products tested (natural vegetable cream, asparagus cream, traditional soup, homemade-style traditional soup, vegetable soup, and vichyssoise) for up to 30 days at 6, 15, and 22 degrees C. A collection of strains isolated from spoiled purees showed slightly higher resistance to AS-48 in the order Paenibacillus sp. > Bacillus macroides > B. cereus, although they were also completely inhibited in natural vegetable cream by AS-48 at 10 microg/ml. However, cocktails of five or eight strains composed of B. cereus (three strains), B. macroides (two strains), and Paenibacillus sp., Paenibacillus polymyxa, and Paenibacillus amylolyticus showed higher bacteriocin resistance with AS-48 of up to 50 microg/ml required for complete inactivation in natural vegetable cream stored at 22 degrees C. Repetitive extragenic palindromic sequence-based PCR (REP-PCR) analysis showed that paenibacilli (along with some B. cereus) was the predominant survivor in the cocktails after bacteriocin treatment. To increase the effectiveness of enterocin AS-48, the bacteriocin was tested (at 20 microg/ml) against the eight-strain cocktail in natural vegetable cream in combination with other antimicrobials. The combination of AS-48 and nisin had a slight but significant additive effect. Bactericidal activity was greatly enhanced by phenolic compounds (carvacrol, eugenol, geraniol, and hydrocinnamic acid), achieving a rapid and complete inactivation of bacilli in the tested puree at 22 degrees C.

Virulence of Bacillus cereus: A multivariate analysis

Biological activity and presence of DNA sequences related to virulence genes were studied in 21 strains of the Bacillus cereus group. The activity of spent culture supernatants and the effect of infection by vegetative bacterial cells were assessed on cultured human enterocytes (Caco-2 cells). The effect of extracellular factors on the detachment, necrosis and mitochondrial dehydrogenase activity of cultured human enterocytes was studied. Hemolytic activity on rabbit red blood cells was also evaluated and the effect of direct procaryotic-eucaryotic interactions was assessed in infection assays with vegetative bacterial cells. Concerning virulence genes, presence of the DNA sequences corresponding to the genes entS, entFM, nhe (A, B and C), sph, hbl (A, B, C and D), piplC and bceT was assessed by PCR. Ribopatterns were determined by an automated riboprinting analysis after digestion of the DNA with EcoRI. Principal component analysis and biplots were used to address the relationship between variables. Results showed a wide range of biological activities: decrease in mitochondrial dehydrogenase activity, necrosis, cell detachment and hemolytic activity. These effects were strain-dependent. Concerning the occurrence of the DNA sequences tested, different patterns were found. In addition, ribotyping showed that strains under study grouped into two main clusters. One of these clusters includes all the strains that were positive for all the DNA sequences tested. Positive and negative correlations between variables under study were evidenced. Interestingly, high detaching strains were positively correlated with the presence of the sequences entS, nheC and sph. Within gene complexes, high correlation was found between sequences of the hbl complex. In contrast, sequences of the nhe complex were not correlated. Some strains clustered together in the biplots. These strains were positive for all the DNA sequences tested and they were able to detach enterocytes upon infection. Our results highlight the multifactorial character of the virulence of the B. cereus group and show the correlation between ribopatterns, occurrence of toxin genes and biological activity of the strains under study.

Food poisoning associated with pumilacidin-producing Bacillus pumilus in rice

Food poisoning caused by other Bacillus species than B. cereus has been described, but the toxins involved have rarely been isolated. Endospores will survive heat treatment and will germinate and multiply in cooked foods producing toxins under appropriate conditions. We describe a small food poisoning outbreak where three people became ill after a dinner in a Chinese restaurant. Acute symptoms including dizziness, headache, chills and back pain developed during the meal, and a few hours later they got stomach cramps and diarrhoea which lasted for several days. Cooked, reheated rice was the prime suspect of the food poisoning, and from the rice large numbers of Bacillus pumilus were isolated. The isolated B. pumilus strain was found to produce a complex of lipopeptides known as pumilacidins with the highest amounts produced at 15 degrees C. This is the first report on isolation of a pumilacidin-producing B. pumilus strain from food implicated in food poisoning and characterization of the organism and the toxin complex involved.

Virulence factor profiles and antimicrobial susceptibilities of ocular bacillus isolates

Bacillus causes one of the most rapidly blinding intraocular infections: endophthalmitis. In this study, Bacillus spp. were isolated from ocular infection cases, taxonomically characterized by riboprint analysis, and screened for the presence of putative virulence factors. The ability of these isolates to kill retinal and corneal cells was examined, as were antibiotic susceptibility profiles. The majority of isolates belonged to the B. cereus taxonomic group of microorganisms and were identified as B. cereus (53%) or B. thuringiensis (26%). Toxins were identified in most B. thuringiensis and B. cereus isolates. Most B. cereus and B. thuringiensis killed corneal and retinal cells within 6 h. All isolates were susceptible to most antibiotics tested, with quinolones and vancomycin being the most potent. These findings represent the first report of B. thuringiensis as an important ocular pathogen, demonstrates the potential ocular toxicity of B. cereus and B. thuringiensis isolates, and identifies antibiotics whose efficacy against Bacillus were superior to those used clinically.

Bio-deposition of a calcium carbonate layer on degraded limestone by Bacillus species

To obtain a restoring and protective calcite layer on degraded limestone, five different strains of the Bacillus sphaericus group and one strain of Bacillus lentus were tested for their ureolytic driven calcium carbonate precipitation. Although all the Bacillus strains were capable of depositing calcium carbonate, differences occurred in the amount of precipitated calcium carbonate on agar plate colonies. Seven parameters involved in the process were examined: calcite deposition on limestone cubes, pH increase, urea degrading capacity, extracellular polymeric substances (EPS)-production, biofilm formation, zeta-potential and deposition of dense crystal layers. The strain selection for optimal deposition of a dense CaCO(3) layer on limestone, was based on decrease in water absorption rate by treated limestone. Not all of the bacterial strains were effective in the restoration of deteriorated Euville limestone. The best calcite precipitating strains were characterised by high ureolytic efficiency, homogeneous calcite deposition on limestone cubes and a very negative zeta-potential.

Rapid Ped-2E9 cell-based cytotoxicity analysis and genotyping of Bacillus species

Bacillus species causing food-borne disease produce multiple toxins eliciting gastroenteritis. Toxin assays with mammalian cell cultures are reliable but may take 24 to 72 h to complete and also lack sensitivity. Here, a sensitive and rapid assay was developed using a murine hybridoma Ped-2E9 cell model. Bacillus culture supernatants containing toxins were added to a Ped-2E9 cell line and analyzed for cytotoxicity with an alkaline phosphatase release assay. Most Bacillus cereus strains produced positive cytotoxicity results within 1 h, and data were comparable to those obtained with the standard Chinese hamster ovary (CHO)-based cytotoxicity assay, which took about 72 h to complete. Moreover, the Ped-2E9 cell assay had 25- to 58-fold-higher sensitivity than the CHO assay. Enterotoxin-producing Bacillus thuringiensis also gave positive results with Ped-2E9 cells, while several other Bacillus species were negative. Eight isolates from food suspected of Bacillus contamination were also tested, and only one strain, which was later confirmed as B. cereus, gave a positive result. In comparison with two commercial diarrheal toxin assay kits (BDE-VIA and BCET-RPLA), the Ped-2E9 assay performed more reliably. Toxin fractions of >30 kDa showed the highest degree of cytotoxicity effects, and heat treatment significantly reduced the toxin activity, indicating the involvement of a heat-labile high-molecular-weight component in Ped-2E9 cytotoxicity. PCR results, in most cases, were in agreement with the cytotoxic potential of each strain. Ribotyping was used to identify cultures and indicated differences for several previously reported isolates. This Ped-2E9 cell assay could be used as a rapid (approximately 1-h) alternative to current methods for sensitive detection of enterotoxins from Bacillus species.

Establishment of a novel multiplex PCR assay and detection of toxigenic strains of the species in the Bacillus cereus group

Five different enterotoxins and one emetic toxin of Bacillus cereus have been characterized. To amplify all of the enterotoxin and emetic-specific sequences of the species in the B. cereus group, a multiplex PCR with 12 primer pairs was established. In developing the assay method, a common terminal sequence at the 3' ends of all primers was chosen and a hot start Taq polymerase was used to overcome primer dimer formation. The assay was successfully applied to analyze the toxigenic potential of 162 food-poisoning and food-related strains. Results showed that there were 10 toxigenic patterns for all the test strains. All of the B. cereus strains carried at least one toxin gene. More than 70% of Bacillus mycoides strains carried no known toxin genes. The toxin profiles and toxin genes of B. mycoides strains were significantly different from B. cereus strains (P < 0.05), although the two species were closely related. The results suggest that many B. mycoides strains might be less prone to cause food poisoning. They also indicate the importance of detecting the toxin genes together with the detection of the species in the B. cereus group.

Toxin-producing ability among Bacillus spp. outside the Bacillus cereus group

A total of 333 Bacillus spp. isolated from foods, water, and food plants were examined for the production of possible enterotoxins and emetic toxins using a cytotoxicity assay on Vero cells, the boar spermatozoa motility assay, and a liquid chromatography-mass spectrometry method. Eight strains produced detectable toxins; six strains were cytotoxic, three strains produced putative emetic toxins (different in size from cereulide), and one strain produced both cytotoxin(s) and putative emetic toxin(s). The toxin-producing strains could be assigned to four different species, B. subtilis, B. mojavensis, B. pumilus, or B. fusiformis, by using a polyphasic approach including biochemical, chemotaxonomic, and DNA-based analyses. Four of the strains produced cytotoxins that were concentrated by ammonium sulfate followed by dialysis, and two strains produced cytotoxins that were not concentrated by such a treatment. Two cultures maintained full cytotoxic activity, two cultures reduced their activity, and two cultures lost their activity after boiling. The two most cytotoxic strains (both B. mojavensis) were tested for toxin production at different temperatures. One of these strains produced cytotoxin at growth temperatures ranging from 25 to 42 degrees C, and no reduction in activity was observed even after 24 h of growth at 42 degrees C. The strains that produced putative emetic toxins were tested for the influence of time and temperature on the toxin production. It was shown that they produced putative emetic toxin faster or just as fast at 30 as at 22 degrees C. None of the cytotoxic strains produced B. cereus-like enterotoxins as tested by PCR or by immunological methods.

Identification and partial characterization of the nonribosomal peptide synthetase gene responsible for cereulide production in emetic Bacillus cereus

Cereulide, a depsipeptide structurally related to valinomycin, is responsible for the emetic type of gastrointestinal disease caused by Bacillus cereus. Due to its chemical structure, (D-O-Leu-D-Ala-L-O-Val-L-Val)(3), cereulide might be synthesized nonribosomally. Therefore, degenerate PCR primers targeted to conserved sequence motifs of known nonribosomal peptide synthetase (NRPS) genes were used to amplify gene fragments from a cereulide-producing B. cereus strain. Sequence analysis of one of the amplicons revealed a DNA fragment whose putative gene product showed significant homology to valine activation NRPS modules. The sequences of the flanking regions of this DNA fragment revealed a complete module that is predicted to activate valine, as well as a putative carboxyl-terminal thioesterase domain of the NRPS gene. Disruption of the peptide synthetase gene by insertion of a kanamycin cassette through homologous recombination produced cereulide-deficient mutants. The valine-activating module was highly conserved when sequences from nine emetic B. cereus strains isolated from diverse geographical locations were compared. Primers were designed based on the NRPS sequence, and the resulting PCR assay, targeting the ces gene, was tested by using a panel of 143 B. cereus group strains and 40 strains of other bacterial species showing PCR bands specific for only the cereulide-producing B. cereus strains.

Bacillus cereus, the causative agent of an emetic type of food-borne illness

Bacillus cereus is the causative agent of two distinct forms of gastroenteritic disease connected to food-poisoning. It produces one emesis-causing toxin and three enterotoxins that elicit diarrhea. Due to changing lifestyles and eating habits, B. cereus is responsible for an increasing number of food-borne diseases in the industrial world. In the past, most studies concentrated on the diarrhoeal type of food-borne disease, while less attention has been given to the emetic type of the disease. The toxins involved in the diarrhoeal syndrome are well-known and detection methods are commercially available, whereas diagnostic methods for the emetic type of disease have been limited. Only recently, progress has been made in developing identification methods for emetic B. cereus and its corresponding toxin. We will summarize the data available for the emetic type of the disease and discuss some new insights in emetic strain characteristics, diagnosis, and toxin synthesis.