Bacillus cereus in a whey process

Identification and Pathogenic Potential of Bacillus cereus Strains Isolated from a Dairy Processing Plant Producing PDO Taleggio Cheese

Low levels of contamination by Bacillus cereus at the cheese farm is essential for reducing any opportunity for growth prior consumption. In this study, B. cereus distribution in a plant producing Protected Designation of Origin Taleggio cheese was investigated and the virulence potential of the isolates was evaluated. Seventy-four samples were collected from Food and Non Food Contact Surfaces (FCS, NFCS), saline curd, and Taleggio. The eleven isolates were identified, typified, and clustered. Strains were tested for the production of hemolysins, hemolysin BL (HBL), phosphatidylcholine-specific phospholipase C (PC-PLC), proteases, and biofilm, and for the presence of chromosomal toxin-encoding genes (sph, plcA, cytK, entFM, bcet, entS, nheA, nheB, nheC). B. cereus was detected on NFCS, FCS, and curd, but not in Taleggio. The isolates were grouped into six clusters, and all produced PC-PLC, hemolysins, and proteases, and most of them HBL (66.7%). All the clusters harbored the nheA, sph, plcA, entFM, and cytK genes, and some also nheB (83.3%), nheC (66.7%), bcet (50.0%), and entS (66.7%). All strains showed biofilm-forming ability. Our data reveal possible contamination of production plants and cheese curd by potentially virulent B. cereus, but bacterial absence in Taleggio highlights the efficacy of a proper management of the production phases in assuring consumer's protection.

Genes under positive selection in the core genome of pathogenic Bacillus cereus group members

In this comparative genomics study our aim was to unravel genes under positive selection in the core genome of the Bacillus cereus group. Indeed, the members of this group share close genetic relationships but display a rather large phenotypic and ecological diversity, providing a unique opportunity for studying how genomic changes reflect ecological adaptation during the divergence of a bacterial group. For this purpose, we screened ten completely sequenced genomes of four pathogenic Bacillus species, finding that 254 out of 3093 genes have codon sites with d_N/d_S (ω) values above one. These results remained unchanged after having disentangled the confounding effects of recombination and selection signature in a Bayesian framework. The presumably adaptive nucleotide polymorphisms are distributed over a wide range of biological functions, such as antibiotic resistance, DNA repair, nutrient uptake, metabolism, cell wall assembly and spore structure. Our results indicate that adaptation to animal hosts, whether as pathogens, saprophytes or symbionts, is the major driving force in the evolution of the Bacillus cereus group. Future work should seek to understand the evolutionary dynamics of both core and accessory genes in an integrative framework to ultimately unravel the key networks involved in host adaptation.

Role of fatty acids in Bacillus environmental adaptation

The large bacterial genus Bacillus is widely distributed in the environment and is able to colonize highly diverse niches. Some Bacillus species harbor pathogenic characteristics. The fatty acid (FA) composition is among the essential criteria used to define Bacillus species. Some elements of the FA pattern composition are common to Bacillus species, whereas others are specific and can be categorized in relation to the ecological niches of the species. Bacillus species are able to modify their FA patterns to adapt to a wide range of environmental changes, including changes in the growth medium, temperature, food processing conditions, and pH. Like many other Gram-positive bacteria, Bacillus strains display a well-defined FA synthesis II system that is equilibrated with a FA degradation pathway and regulated to efficiently respond to the needs of the cell. Like endogenous FAs, exogenous FAs may positively or negatively affect the survival of Bacillus vegetative cells and the spore germination ability in a given environment. Some of these exogenous FAs may provide a powerful strategy for preserving food against contamination by the Bacillus pathogenic strains responsible for foodborne illness.

Sources of Bacillus cereus contamination in a pasteurized zucchini purée processing line, differentiated by two PCR-based methods

In previous work, raw materials used for processing pasteurized zucchini purée (zucchini, milk proteins and starch) and cultivation soil of zucchinis were found to be potential sources of stored product contamination with Bacillus cereus. 134 B. cereus strains originating from these sources and from the stored product were typed using coliphage M13 sequence-based polymerase chain reaction (M13-PCR) and DNA amplification fingerprinting. Combined patterns from the two methods were compared using Dice's coefficient and the unweighted pair group method with average cluster analysis. 16 combined profile groups and six unclustered strains were formed at 75% similarity level. Representative strains of each group were subsequently examined for growth at low temperature (4 degrees C, 7 degrees C and 10 degrees C). Based on strain relatedness, five major groups and two minor groups among the nine groups containing zucchini strains were common to both zucchini and soil origins, indicating that the soil was the main initial source of contamination for zucchinis. Strains from zucchinis and soil were heterogeneous compared with strains from dehydrated ingredients (milk proteins and starch), and were mainly composed of psychrotrophic strains. Convergent results from molecular typing and growth at low temperature showed that psychrotrophic contaminants of the stored product originated from zucchinis, whereas non-psychrotrophic contaminants originated from milk proteins. The number of genetic groups decreased during the purée processing, suggesting selection of strains during zucchini washing operations, heat treatment and storage.

Phenotypic and genotypic diversity of Bacillus cereus isolates recovered from honey

Of 433 honey samples collected in Argentina, 114 (27%) yielded Bacillus cereus isolates (27%) and 60 (14%) yielded other species of Bacillus. The Argentinian B. cereus isolates were compared with isolates recovered from honey from other countries (n=16) and with strain ATCC 11718. The 133 B. cereus isolates and the ATCC strain were characterized using rep-PCR fingerprinting with primers BOX, REP and ERIC, restriction fragment length polymorphism analysis of a 16S rRNA gene fragment (16S rRNA PCR/RFLP), and morphological and biochemical tests. There was a high degree of diversity, both phenotypic and genotypic among the isolates of B. cereus. Our results demonstrate the usefulness of rep-PCR genomic fingerprinting for characterizing populations of B. cereus. According to our knowledge, this is the first report of phenotypic and genotypic characterization of B. cereus isolates from honey.

Polyhydroxyalkanoates in Gram-positive bacteria: insights from the genera Bacillus and Streptomyces

Gram-positive bacteria, notably Bacillus and Streptomyces, have been used extensively in industry. However, these microorganisms have not yet been exploited for the production of the biodegradable polymers, polyhydroxyalkanoates (PHAs). Although PHAs have many potential applications, the cost of production means that medical applications are currently the main area of use. Gram-negative bacteria, currently the only commercial source of PHAs, have lipopolysaccharides (LPS) which co-purify with the PHAs and cause immunogenic reactions. On the other hand, Gram- positive bacteria lack LPS, a positive feature which justifies intensive investigation into their production of PHAs. This review summarizes currently available knowledge on PHA production by Gram- positive bacteria especially Bacillus and Streptomyces. We hope that this will form the basis of further research into developing either or both as a source of PHAs for medical applications.

Survival and growth characteristics of Escherichia coli O157:H7 in pasteurized and unpasteurized Cheddar cheese whey

The objective of this study was to determine the survival and growth characteristics of Escherichia coli O157:H7 in whey. A five-strain mixture of E. coli O157:H7 was inoculated into 100 ml of fresh, pasteurized or unpasteurized Cheddar cheese whey (pH 5.5) at 10(5) or 10(2) CFU/ml, and stored at 4, 10 or 15 degrees C. The population of E. coli O157:H7 (on Sorbitol MacConkey agar supplemented with 0.1% 4-methylumbelliferyl-beta-D-glucuronide) and lactic acid bacteria (on All Purpose Tween agar) were determined on days 0, 1, 4, 7, 14, 21 and 28. At all storage temperatures, survival of E. coli O157:H7 was significantly higher (P<0.01) in the pasteurized whey compared to that in the unpasteurized samples. At 10 and 15 degrees C, E. coli O157:H7 in pasteurized whey significantly (P<0.05) increased during the first week of storage, followed by a decrease thereafter. However at the same temperatures, E. coli O157:H7 exhibited a steady decline in the unpasteurized samples from day 0. At 4 degrees C, E. coli O157:H7 did not grow in pasteurized and unpasteurized whey; however, the pathogen persisted longer in pasteurized samples. At all the three storage temperatures, E. coli O157:H7 survived up to day 21 in the pasteurized and unpasteurized whey. The initial load of lactic acid bacteria in the unpasteurized whey samples was approximately 7.0 log10 CFU/ml and, by day 28, greater than 3.0 log10 CFU/ml of lactic acid bacteria survived in unpasteurized whey at all temperatures, with the highest counts recovered at 4 degrees C. Results indicate the potential risk of persistence of E. coli O157:H7 in whey in the event of contamination with this pathogen.

Recontamination as a source of pathogens in processed foods

Food products that have been submitted to an adequate heat-treatment during processing are free of vegetative pathogens and, depending on the treatments, of sporeformers and are generally regarded as safe. Processed products such as pâté, ice cream, infant formulae and others have nevertheless been responsible for food-borne illnesses. Thorough epidemiological investigations of several of these outbreaks have demonstrated that the presence of vegetative pathogens such as Salmonella spp. or Listeria monocytogenes in the consumed products was frequently due to post-process recontamination. The majority of studies on pathogens in foods are devoted to investigations on their presence in raw materials or on their growth and behaviour in the finished products. Reference to recontamination is, however, only made in relatively few publications and very little is published on the sources and routes of these pathogens into products after the final lethal processing step. The investigation of an outbreak, including epidemiological studies and typing of strains, is very useful to trace the origin and source of the hazard. Published data demonstrate that the presence of pathogens in the vicinity of unprotected product in processing lines represents a significant risk of recontamination. Microbiological Risk Assessment studies can be conducted as part of governmental activities determining appropriate protection levels for populations. Although recontamination has been identified as a relevant cause of food incidences, it is often not considered in such studies. This paper advocates that an effort should be made to develop our knowledge and information on recontamination further and start using it systematically in the exposure assessment part of Microbiological Risk Assessment studies.

Shelf Life and Safety Concerns of Bakery Products—A Review

Bakery products are an important part of a balanced diet and, today, a wide variety of such products can be found on supermarket shelves. This includes unsweetened goods (bread, rolls, buns, crumpets, muffins and bagels), sweet goods (pancakes, doughnuts, waffles and cookies) and filled goods (fruit and meat pies, sausage rolls, pastries, sandwiches, cream cakes, pizza and quiche). However, bakery products, like many processed foods, are subject to physical, chemical and microbiological spoilage. While physical and chemical spoilage limits the shelf life of low and intermediate moisture bakery products, microbiological spoilage by bacteria, yeast and molds is the concern in high moisture products i.e., products with a water activity (a(w)) > 0.85. Furthermore, several bakery products also have been implicated infoodborne illnesses involving Salmonella spp., Listeria monoctyogenes and Bacillus cereus, while Clostridium botulinum is a concern in high moisture bakery products packaged under modified atmospheres. This extensive review is divided into two parts. Part I focuses on the spoilage concerns of low, intermediate and high moisture bakery products while Part II focuses on the safety concerns of high moisture bakery products only. In both parts, traditional and novel methods of food preservation that can be used by the bakery industry to extend the shelf life and enhance the safety of products are discussed in detail.

Identification of bacteria in pasteurized zucchini purées stored at different temperatures and comparison with those found in other pasteurized vegetable purées

One hundred nineteen isolates from a commercial zucchini purée stored at 4, 10, and 20 to 25 degrees C were fingerprinted using repetitive sequence-based PCR (REP-PCR) and classified into 35 REP types. One representative isolate of each REP type was subsequently identified by API50CHB/20E profile and partial rrs gene sequence analysis. Nine REP types were misidentified by the API system. Strains were misidentified as being in the Bacillus circulans (group 2) API taxon or in taxa with a low number of positive API characters such as Brevibacillus brevis. A phylogenetic analysis pointed to one new species of Bacillus and three new species of Paenibacillus among the misidentified REP types. Bacterial components in zucchini purée were compared phenotypically with those obtained in previous work on broccoli, carrot, leek, potato, and split pea purées, based on simple matching coefficient and unweighted pair group method with averages cluster analysis. Out of 254 strains, 69 strains previously identified as B. circulans (group 2) or B. circulans/B. macerans/B. polymyxa were assigned to a new Paenibacillus taxon phylogenetically related to P. azotofixans. Storage conditions at 4 degrees C favored the development of "B. macroides/B. maroccanus" and Paenibacillus spp. in zucchini purées and Paenibacillus spp. in other purées. Storage conditions at 20 to 25 degrees C favored the development of B. subtilis group (B. licheniformis and B. subtilis) and B. cereus group strains. At 10 degrees C, Paenibacillus spp. were always present at high frequencies, whereas the occurrence of B. macroides/B. maroccanus (in zucchini purées), B. cereus, and B. pumilus varied with the experiment.

Prevalence and behaviour of Bacillus cereus in a REPFED of Italian origin

This paper reports on the prevalence and behaviour of Bacillus cereus in gnocchi, a REPFED of Italian origin. A survey of gnocchi under varying storage conditions, revealed that, although B. cereus was found in 33% of the samples, the contamination level was lower than 10(2) CFU/g for the unstored and the refrigerated (8 degrees C) samples. Counts increased with increasing storage temperatures and prolonged storage times in samples prepared without sorbic acid. The effect of different formulations (sorbic, citric and lactic acid) and storage conditions (8, 12 and 20 degrees C) have been evaluated in a challenge testing with spores of B. cereus. Results indicate that the use of sorbic acid in association with citric or lactic acid to pH 5.0 is effective in inhibiting growth of B. cereus and the anticipated shelf life of the product is safe even if temperature abuse occurs. If sorbic acid is omitted, lactic acid can inhibit B. cereus growth during storage at 8 degrees C. On the contrary, when temperature abuse occurs (12 and 20 degrees C), lactic or citric acid are not able to prevent growth of B. cereus.

Properties of Bacillus cereus and other bacilli contaminating biomaterial-based industrial processes

This paper is an overview on bacilli in industrial processes, with focus on food grade paper and paperboard production. Paperboards mainly contain sporeforming bacteria belonging to the genera Bacillus, Paenibacillus and Brevibacillus, usually found in quantities from < 50 to 250 cfu g(-1) homogenized paperboard. Of those frequently found, Bacillus cereus group, B. licheniformis, B. subtilis and Brevibacillus brevis are important for food hygiene because of their hydrolytic activities on food components and the ability of some strains to produce food poisoning toxins or to grow at refrigerated temperatures. We found that the phenotypic properties (lecithinase activity, nitrate reduction) used in standard methods (e.g., ISO, FDA, IDF) to recognize B. cereus, were unreliable for industrial isolates. Whole cell fatty acid composition of a group of the industrial isolates deviated so much from those in a widely used commercial database that the strains were not or only poorly recognized as B. cereus. Industrial isolates, including toxigenic ones, often missed one or more of these characters, even in cases where 100% 16S rDNA identity was found with B. cereus or with B. thuringiensis. 11-Methyldodecanoic acid and trans-9-hexadecenoic acid were found without exception in over 200 industrial B. cereus group isolates and in over 30 culture collection strains. The detection of these fatty acids is a secure method for the identification of B. cereus. Negative reaction for starch hydrolysis and for BCET-RPLA test and a specific ribotype were found in all B. cereus strains producing the emetic toxin.

Evaluation of methods for recognising strains of the Bacillus cereus group with food poisoning potential among industrial and environmental contaminants

Toxin production, biochemical properties and ribotypes of Bacillus cereus group (B. cereus, B. thuringiensis, B. mycoides) strains originating from industrial and environmental sources (n = 64), from food poisoning incidents (n = 22) and from reference sources (n = 7) were analysed. Forty ribotypes were found among the 93 strains. Eleven strains from food poisoning incidents produced emetic (mitochondrio) toxin, as determined by the boar spermatozoa toxicity test. These strains possessed closely similar ribotypes which were rare among strains of other origins. Sperm toxin producing (cereulide positive) strains did not hydrolyse starch and did not produce haemolysin BL, as determined by the reverse passive latex agglutination test. Sixteen different ribotypes were found among B. cereus strains from board machines (n = 16) and from packaging board (n = 16), indicating many different sources of B. cereus contamination in board mills. Strains originating from packaging board had predominantly different ribotypes from those of dairy and dairy product originating strains. Nine (53%) out of 17 strains from a single dairy process shared the same ribotype whereas strains from milk and milk products from different dairies had different ribotypes indicating that B. cereus group populations were dairy specific. Twenty-two percent of strains isolated from the paperboard industry on non-selective medium were lecithinase negative, including enterotoxin producing strains. This stresses the importance of other detection methods not based on a positive lecithinase reaction.