Analysis of emetic toxin production by Bacillus species using cellular cytotoxicity, molecular, and chromatographic assays

Phenotypic homogeneity of emetic Bacillus cereus isolates in China

Emetic Bacillus cereus strains produce a potent cereulide cytotoxin, which can cause acute and fatal cases of food poisoning. We isolated 18 emetic B. cereus strains from a food poisoning event, and from clinical and non-random food surveillance in China and phenotypic characteristics of haemolysis, starch hydrolysis, salicin fermentation, gelatin liquefaction, cytotoxicity, and susceptibility to antibiotics were assessed. All isolates were positive for haemolysis and gelatin liquefaction, and negative for starch hydrolysis and salicin fermentation. Their haemolytic potentials were intermediate to Bacillus anthracis and B. cereus ATCC 14579 (a non-emetic strain). All isolates were cytotoxic to CHO, Hep-2, and Vero cells, and were sensitive to ampicillin. The homogeneous phenotypes of emetic isolates from China are similar to the corresponding traits of European and Japanese isolates that have been characterized, suggesting highly similar phenotypes of emetic B. cereus worldwide.

Bacillus cereus food intoxication and toxicoinfection

Bacillus cereus is one of the leading etiological agents of toxin-induced foodborne diseases. Its omnipresence in different environments, spore formation, and its ability to adapt to varying conditions and produce harmful toxins make this pathogen a health hazard that should not be underestimated. Food poisoning by B. cereus can manifest itself as an emetic or diarrheal syndrome. The former is caused by the release of the potent peptide toxin cereulide, whereas the latter is the result of proteinaceous enterotoxins (e.g., hemolysin BL, nonhemolytic enterotoxin, and cytotoxin K). The final harmful effect is not only toxin and strain dependent, but is also affected by the stress responses, accessory virulence factors, and phenotypic properties under extrinsic, intrinsic, and explicit food conditions and host-related environment. Infamous portrait of B. cereus as a foodborne pathogen, as well as a causative agent of nongastrointestinal infections and even nosocomial complications, has inspired vast volumes of multidisciplinary research in food and clinical domains. As a result, extensive original data became available asking for a new, both broad and deep, multifaceted look into the current state-of-the art regarding the role of B. cereus in food safety. In this review, we first provide an overview of the latest knowledge on B. cereus toxins and accessory virulence factors. Second, we describe the novel taxonomy and some of the most pertinent phenotypic characteristics of B. cereus related to food safety. We link these aspects to toxin production, overall pathogenesis, and interactions with its human host. Then we reflect on the prevalence of different toxinotypes in foods opening the scene for epidemiological aspects of B. cereus foodborne diseases and methods available to prevent food poisoning including overview of the different available methods to detect B. cereus and its toxins.

Propidium monoazide conventional PCR and DNA sequencing: detection of negative culture bacterial pathogens causing subclinical mastitis

AIMS

This study was conducted to early detect the negative culture bacterial pathogens causing subclinical mastitis for the fast diagnosis of the disease and the reduction of some milk-transmitted pathogenic bacteria to human consumers.

METHODS AND RESULTS

A total of 171 positive California mastitis test (CMT) milk samples collected from asymptomatic dairy cows in Sharkia Governorate, Egypt were examined by conventional bacteriological methods. The obtained results revealed that Streptococcus species (77·2%), followed by Staphylococcus species (48·6%) and Escherichia coli (25·7%) were the most predominant bacterial pathogens isolated from positive culture milk samples, whereas Enterobacter and Pseudomonas species were the lowest ones (1·2%, for each). Herein, 13 (7.6%) negative culture milk samples were subjected to propidium monoazide (PMA) conventional PCR assay, followed by DNA sequencing of purified PCR amplicons. Sequence analysis identified seven different types of negative culture bacterial pathogens comprising as following; 4 Enterococcus hirae, 2 Bacillus cereus, 2 Staphylococcus aureus, 1 Bacillus mycoides, 1 Bacillus subtilis, 1 Enterococcus faecium and 1 Escherichia coli.

CONCLUSIONS

All the detected negative culture bacterial pathogens by PMA-PCR assay, followed by DNA sequencing were incriminated in causing subclinical mastitis disease and had serious implications on human public health through consumption of milk contaminated with those recovered bacterial pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

The used methods could be useful in the routine detection of negative culture bacterial pathogens present in milk and consequently, it will help in the rapid diagnosis of subclinical mastitis disease and the reduction of many milk-transmitted diseases to human.

Scientific Opinion on the update of the list of QPS-recommended biological agents intentionally added to food or feed as notified to EFSA

EFSA is requested to assess the safety of a broad range of biological agents in the context of notification for market authorisation as sources of food and feed additives, food enzymes and plant protection products. The qualified presumption of safety (QPS) assessment was developed to provide a harmonised generic pre-assessment to support safety risk assessments performed by EFSA's scientific Panels. The safety of unambiguously defined biological agents (at the highest taxonomic unit appropriate for the purpose for which an application is intended), and the completeness of the body of knowledge are assessed. Identified safety concerns for a taxonomic unit are, where possible and reasonable in number, reflected as 'qualifications' in connection with a recommendation for a QPS status. The list of QPS recommended biological agents was reviewed and updated in the current opinion and therefore becomes the valid list. The 2016 update reviews previously assessed microorganisms including bacteria, yeasts and viruses used for plant protection purposes following an Extensive Literature Search strategy. The taxonomic units related to the new notifications received since the 2013 QPS opinion, were periodically evaluated for a QPS status and the results published as Statements of the BIOHAZ Panel. Carnobacterium divergens, Lactobacillus diolivorans, Microbacterium imperiale, Pasteuria nishizawae, Pediococcus parvulus, Bacillus flexus, Bacillus smithii, Xanthomonas campestris and Candida cylindracea were recommended for the QPS list. All taxonomic units previously recommended for the 2013 QPS list had their status reconfirmed as well their qualifications with the exception of Pasteuria nishizawae for which the qualification was removed. The exclusion of filamentous fungi and enterococci from the QPS evaluations was reconsidered but monitoring will be maintained and the status will be re-evaluated in the next QPS Opinion update. Evaluation of bacteriophages should remain as a case-by-case procedure and should not be considered for QPS status.

The Prevalence and Control of Bacillus and Related Spore-Forming Bacteria in the Dairy Industry

Milk produced in udder cells is sterile but due to its high nutrient content, it can be a good growth substrate for contaminating bacteria. The quality of milk is monitored via somatic cell counts and total bacterial counts, with prescribed regulatory limits to ensure quality and safety. Bacterial contaminants can cause disease, or spoilage of milk and its secondary products. Aerobic spore-forming bacteria, such as those from the genera Sporosarcina, Paenisporosarcina, Brevibacillus, Paenibacillus, Geobacillus and Bacillus, are a particular concern in this regard as they are able to survive industrial pasteurization and form biofilms within pipes and stainless steel equipment. These single or multiple-species biofilms become a reservoir of spoilage microorganisms and a cycle of contamination can be initiated. Indeed, previous studies have highlighted that these microorganisms are highly prevalent in dead ends, corners, cracks, crevices, gaskets, valves and the joints of stainless steel equipment used in the dairy manufacturing plants. Hence, adequate monitoring and control measures are essential to prevent spoilage and ensure consumer safety. Common controlling approaches include specific cleaning-in-place processes, chemical and biological biocides and other novel methods. In this review, we highlight the problems caused by these microorganisms, and discuss issues relating to their prevalence, monitoring thereof and control with respect to the dairy industry.

A RAPD based study revealing a previously unreported wide range of mesophilic and thermophilic spore formers associated with milk powders in China

Aerobic spore forming bacteria are potential milk powder contaminants and are viewed as indicators of poor quality. A total of 738 bacteria, including both mesophilic and thermophilic, isolated from twenty-five powdered milk samples representative of three types of milk powders in China were analyzed based on the random amplified polymorphic DNA (RAPD) protocol to provide insight into species diversity. Bacillus licheniformis was found to be the most prevalent bacterium with greatest diversity (~43% of the total isolates) followed by Geobacillus stearothermophilus (~21% of the total isolates). Anoxybacillus flavithermus represented only 8.5% of the total profiles. Interestingly, actinomycetes represented a major group of the isolates with the predominance of Laceyella sacchari followed by Thermoactinomyces vulgaris, altogether comprising of 7.3% of the total isolates. Out of the nineteen separate bacterial species (except five unidentified groups) recovered and identified from milk powders, twelve proved to belong to novel or previously unreported species in milk powders. Assessment and characterization of the harmful effects caused by this particular micro-flora on the quality and safety of milk powders will be worth doing in the future.