Prevalence of Clostridium botulinum in Finnish trout farms: pulsed-field gel electrophoresis typing reveals extensive genetic diversity among type E isolates

Botulism in fish: a review

Published information about fish botulism is scant. We review here the current literature on fish botulism. Freshwater fish are susceptible to botulism. Only anecdotal evidence exists about possible botulism cases in saltwater fish. With only a few exceptions, the etiology of all cases of fish botulism reported is Clostridium botulinum type E, although fish are sensitive to, and may carry, various C. botulinum types. Clinical signs of botulism in fish include loss of equilibrium and motion, abducted opercula, open mouths, dark pigmentation, and head up/tail down orientation in which attempts to swim result in breaching the surface of the water. Dark pigmentation is thought to be associated with acetylcholine imbalance in botulinum neurotoxin (BoNT)-affected fish. Rarely, but similar to the situation in other animal species, fish can recover from botulism. Fish botulism can cause secondary outbreaks of the disease in birds, as botulism-affected fish stand out from normal fish, and are selectively preyed upon by fish-eating birds, which thus become intoxicated by the BoNT present in sick fish. The source of BoNT in fish has not been definitively confirmed. Fish may ingest C. botulinum spores that then germinate in their digestive tract, but the possibility that fish ingest preformed BoNT from the environment (e.g., dead fish, shellfish, insects) cannot be ruled out. The presumptive diagnosis of botulism in fish is established based on clinical signs, and as in other species, confirmation should be based on detection of BoNT in intestinal content, liver, and/or serum of affected fish.

Food safety in fisheries: Application of One Health approach

Fisheries comprise the fastest growing sector meeting the global protein requirements. Being an affordable enterprise, it is considered a safe source of food and the muscles of healthy fishes are almost sterile. However, a multitude of hazards (biological, chemical, and environmental) can be introduced into aquaculture throughout the production and supply chain. Also, it can originate from unsuitable farming practices, environmental pollution, and socio-cultural habits prevailing in various regions. Hence, with an increasing global population and demands for aquacultural products, assessment and regulation of food safety concerns are becoming significantly evident. Ensuring safe, secure, affordable, and quality food for all in a global context is pragmatically difficult. In this context, it is quite imperative to understand the ecology and dynamics of these hazards throughout the entire production chain in a One Health approach. Here, we discuss the issues and challenges faced in the fisheries sector as a whole and the need for a One Health approach to overcome such hurdles.

Pan-Genomic Analysis of Clostridium botulinum Group II (Non-Proteolytic C. botulinum) Associated with Foodborne Botulism and Isolated from the Environment

The neurotoxin formed by Clostridium botulinum Group II is a major cause of foodborne botulism, a deadly intoxication. This study aims to understand the genetic diversity and spread of C. botulinum Group II strains and their neurotoxin genes. A comparative genomic study has been conducted with 208 highly diverse C. botulinum Group II strains (180 newly sequenced strains isolated from 16 countries over 80 years, 28 sequences from Genbank). Strains possessed a single type B, E, or F neurotoxin gene or were closely related strains with no neurotoxin gene. Botulinum neurotoxin subtype variants (including novel variants) with a unique amino acid sequence were identified. Core genome single-nucleotide polymorphism (SNP) analysis identified two major lineages-one with type E strains, and the second dominated by subtype B4 strains with subtype F6 strains. This study revealed novel details of population structure/diversity and established relationships between whole-genome lineage, botulinum neurotoxin subtype variant, association with foodborne botulism, epidemiology, and geographical source. Additionally, the genome sequences represent a valuable resource for the research community (e.g., understanding evolution of C. botulinum and its neurotoxin genes, dissecting key aspects of C. botulinum Group II biology). This may contribute to improved risk assessments and the prevention of foodborne botulism.

The use of the so-called 'tubs' for transporting and storing fresh fishery products

On-land transport/storage of fresh fishery products (FFP) for up to 3 days in 'tubs' of three-layered poly-ethylene filled with freshwater and ice was compared to the currently authorised practice (fish boxes of high-density poly-ethylene filled with ice). The impact on the survival and growth of biological hazards in fish and the histamine production in fish species associated with a high amount of histidine was assessed. In different modelling scenarios, the FFP are stored on-board in freshwater or seawater/ice (in tubs) and once on-land they are 'handled' (i.e. sorted or gutted and/or filleted) and transferred to either tubs or boxes. The temperature of the FFP was assumed to be the most influential factor affecting relevant hazards. Under reasonably foreseeable 'abusive' scenarios and using a conservative modelling approach, the growth of the relevant hazards (i.e. Listeria monocytogenes, Aeromonas spp. and non-proteolytic Clostridium botulinum), is expected to be < 0.2 log10 units higher in tubs than in boxes after 3 days when the initial temperature of the fish is 0°C ('keeping' process). Starting at 7°C ('cooling-keeping' process), the expected difference in the growth potential is higher (< 1 log10 for A. hydrophila and < 0.5 log10 for the other two hazards) due to the poorer cooling capacity of water and ice (tub) compared with ice (box). The survival of relevant hazards is not or is negligibly impacted. Histamine formation due to growth of Morganella psychrotolerans under the 'keeping' or 'cooling-keeping' process can be up to 0.4 ppm and 1.5 ppm higher, respectively, in tubs as compared to boxes after 3 days, without reaching the legal limit of 100 ppm. The water uptake associated with the storage of the FFP in tubs (which may be up to 6%) does not make a relevant contribution to the differences in microbial growth potential compared to boxes.

Public Health Risk Associated with Botulism as Foodborne Zoonoses

Botulism is a rare but severe neurological disease in man and animals that is caused by botulinum neurotoxins (BoNTs) produced by Clostridium botulinum and atypical strains from other Clostridium and non-Clostridium species. BoNTs are divided into more than seven toxinotypes based on neutralization with specific corresponding antisera, and each toxinotype is subdivided into subtypes according to amino acid sequence variations. Animal species show variable sensitivity to the different BoNT toxinotypes. Thereby, naturally acquired animal botulism is mainly due to BoNT/C, D and the mosaic variants CD and DC, BoNT/CD being more prevalent in birds and BoNT/DC in cattle, whereas human botulism is more frequently in the types A, B and E, and to a lower extent, F. Botulism is not a contagious disease, since there is no direct transmission from diseased animals or man to a healthy subject. Botulism occurs via the environment, notably from food contaminated with C. botulinum spores and preserved in conditions favorable for C. botulinum growth and toxin production. The high prevalence of botulism types C, D and variants DC and CD in farmed and wild birds, and to a lower extent in cattle, raises the risk of transmission to human beings. However, human botulism is much rarer than animal botulism, and botulism types C and D are exceptional in humans. Only 15 cases or suspected cases of botulism type C and one outbreak of botulism type D have been reported in humans to date. In contrast, animal healthy carriers of C. botulinum group II, such as C. botulinum type E in fish of the northern hemisphere, and C. botulinum B4 in pigs, represent a more prevalent risk of botulism transmission to human subjects. Less common botulism types in animals but at risk of transmission to humans, can sporadically be observed, such as botulism type E in farmed chickens in France (1998-2002), botulism type B in cattle in The Netherlands (1977-1979), botulism types A and B in horses, or botulism type A in dairy cows (Egypt, 1976). In most cases, human and animal botulisms have distinct origins, and cross transmissions between animals and human beings are rather rare, accidental events. But, due to the severity of this disease, human and animal botulism requires a careful surveillance.

Inactivation of non-proteolytic Clostridium botulinum type E in low-acid foods and phosphate buffer by heat and pressure

The effect of high pressure thermal (HPT) treatments on the inactivation of spores of non-proteolytic type E Clostridium botulinum TMW 2.990 was investigated at high pressures (300 to 600 MPa) and elevated temperatures (80 to 100 °C) in four low-acid foods (steamed sole, green peas with ham, vegetable soup, braised veal) and imidazole phosphate buffer (IPB). In addition, corresponding conventional thermal treatments at ambient pressure were performed to expose possible synergisms of pressure and temperature on spore inactivation. In general, spore count reduction was more efficient by combining pressure and temperatures < 100 °C and the overall process duration could be shortened due to accelerated heating rates (adiabatic effect). Processing at 90 °C and 600 MPa resulted in inactivation below the detection limit after 5 min in all foods except steamed sole. Traditional thermal processing of spores at 90 °C for 10 min, on the other hand, did not result in an estimated 6-log reduction. Additional HPT treatments in steamed sole and IPB did not reveal pronounced food matrix dependent protective effects. Here, varying pressure levels did not appear to be the driving force for spore count reduction in steamed sole at any temperature. By applying a Weibull distribution on destruction kinetics of isobaric/isothermal holding times, 6D-values were calculated. Compression and decompression phase (1 s pressure holding time) had a considerable impact on spore count reduction (max. -2.9 log units) in both, foods and buffer. Hence, compression and decompression phases should directly be included into the total lethal effect of HPT treatments to avoid prolonged holding times and overprocessing.

Neurotoxin synthesis is positively regulated by the sporulation transcription factor Spo0A in Clostridium botulinum type E

Clostridium botulinum produces the most potent natural toxin, the botulinum neurotoxin (BoNT), probably to create anaerobiosis and nutrients by killing the host, and forms endospores that facilitate survival in harsh conditions and transmission. Peak BoNT production coincides with initiation of sporulation in C. botulinum cultures, which suggests common regulation. Here, we show that Spo0A, the master regulator of sporulation, positively regulates BoNT production. Insertional inactivation of spo0A in C. botulinum type E strain Beluga resulted in significantly reduced BoNT production and in abolished or highly reduced sporulation in relation to wild-type controls. Complementation with spo0A restored BoNT production and sporulation. Recombinant DNA-binding domain of Spo0A directly bound to a putative Spo0A-binding box (CTTCGAA) within the BoNT/E operon promoter, demonstrating direct regulation. Spo0A is the first neurotoxin regulator reported in C. botulinum type E. Unlike other C. botulinum strains that are terrestrial and employ the alternative sigma factor BotR in directing BoNT expression, C. botulinum type E strains are adapted to aquatic ecosystems, possess distinct epidemiology and lack BotR. Our results provide fundamental new knowledge on the genetic control of BoNT production and demonstrate common regulation of BoNT production and sporulation, providing a key intervention point for control.

Pulsotype Diversity of Clostridium botulinum Strains Containing Serotypes A and/or B Genes

Clostridium botulinum strains are prevalent in the environment and produce a potent neurotoxin that causes botulism, a rare but serious paralytic disease. In 2010, a national PulseNet database was established to curate C. botulinum pulsotypes and facilitate epidemiological investigations, particularly for serotypes A and B strains frequently associated with botulism cases in the United States. Between 2010 and 2014 we performed pulsed-field gel electrophoresis (PFGE) using a PulseNet protocol, uploaded the resulting PFGE patterns into a national database, and analyzed data according to PulseNet criteria (UPGMA clustering, Dice coefficient, 1.5% position tolerance, and 1.5% optimization). A retrospective data analysis was undertaken on 349 entries comprised of type A and B strains isolated from foodborne and infant cases to determine epidemiological relevance, resolution of the method, and the diversity of the database. Most studies to date on the pulsotype diversity of C. botulinum have encompassed very small sets of isolates; this study, with over 300 isolates, is more comprehensive than any published to date. Epidemiologically linked isolates had indistinguishable patterns, except in four instances and there were no obvious geographic trends noted. Simpson's Index of Diversity (D) has historically been used to demonstrate species diversity and abundance within a group, and is considered a standard descriptor for PFGE databases. Simpson's Index was calculated for each restriction endonuclease (SmaI, XhoI), the pattern combination SmaI-XhoI, as well as for each toxin serotype. The D values indicate that both enzymes provided better resolution for serotype B isolates than serotype A. XhoI as the secondary enzyme provided little additional discrimination for C. botulinum. SmaI patterns can be used to exclude unrelated isolates during a foodborne outbreak, but pulsotypes should always be considered concurrently with available epidemiological data.

Tracking sources of Clostridium botulinum type E contamination in seal meat

Botulism in Nunavik, Quebec is associated with the consumption of aged marine mammal meat and fat. The objective was to identify meat handling practices presenting a risk of contamination of seal meat with C. botulinum. Potential sources of contamination were assessed through interviews with igunaq producers from five communities of Nunavik. These sources were verified by detection and isolation of C. botulinum from igunaq prepared in the field from seal carcasses. Interviews indicated practices presenting a risk for contamination included: placing meat or fat on coastal rocks, using seawater for rinsing, and ageing meat in inverted seal skin pouches. Although the presence of C. botulinum type E spores was detected in only two of 32 (6.3%) meat or fat samples collected during the butchering process, two of four igunaq preparations from these samples contained type E botulinum toxin. Analysis of C. botulinum type E isolates recovered from these preparations indicated that shoreline soil may be a source of contamination. Seal meat and fat may be contaminated with C. botulinum type E during the butchering process. Measures can be adopted to reduce the risks of contamination in the field and possibly decrease the incidence of type E botulism in Nunavik.

Neutralization of Botulinum Neurotoxin Type E by a Humanized Antibody

Botulinum neurotoxins (BoNTs) cause botulism and are the deadliest naturally-occurring substances known to humans. BoNTs have been classified as one of the category A agents by the Centers for Disease Control and Prevention, indicating their potential use as bioweapons. To counter bio-threat and naturally-occurring botulism cases, well-tolerated antibodies by humans that neutralize BoNTs are relevant. In our previous work, we showed the neutralizing potential of macaque (Macaca fascicularis)-derived scFv-Fc (scFv-Fc ELC18) by in vitro endopeptidase immunoassay and ex vivo mouse phrenic nerve-hemidiaphragm assay by targeting the light chain of the botulinum neurotoxin type E (BoNT/E). In the present study, we germline-humanized scFv-Fc ELC18 into a full IgG hu8ELC18 to increase its immunotolerance by humans. We demonstrated the protection and prophylaxis capacity of hu8ELC18 against BoNT/E in a mouse model. A concentration of 2.5 ng/mouse of hu8ELC18 protected against 5 mouse lethal dose (MLD) in a mouse protection assay and complete neutralization of 1 LD50 of pure BoNT/E toxin was achieved with 8 ng of hu8ELC18 in mouse paralysis assay. Furthermore, hu8ELC18 protected mice from 5 MLD if injected up to 14 days prior to intraperitoneal BoNT/E administration. This newly-developed humanized IgG is expected to have high tolerance in humans.

High pressure thermal inactivation of Clostridium botulinum type E endospores - kinetic modeling and mechanistic insights

Cold-tolerant, neurotoxigenic, endospore forming Clostridium (C.) botulinum type E belongs to the non-proteolytic physiological C. botulinum group II, is primarily associated with aquatic environments, and presents a safety risk for seafood. High pressure thermal (HPT) processing exploiting the synergistic effect of pressure and temperature can be used to inactivate bacterial endospores. We investigated the inactivation of C. botulinum type E spores by (near) isothermal HPT treatments at 300–1200 MPa at 30–75°C for 1 s to 10 min. The occurrence of heat and lysozyme susceptible spore fractions after such treatments was determined. The experimental data were modeled to obtain kinetic parameters and represented graphically by isoeffect lines. In contrast to findings for spores of other species and within the range of treatment parameters applied, zones of spore stabilization (lower inactivation than heat treatments alone), large heat susceptible (HPT-induced germinated) or lysozyme-dependently germinable (damaged coat layer) spore fractions were not detected. Inactivation followed first order kinetics. Dipicolinic acid release kinetics allowed for insights into possible inactivation mechanisms suggesting a (poorly effective) physiologic-like (similar to nutrient-induced) germination at ≤450 MPa/≤45°C and non-physiological germination at >500 MPa/>60–70°C. Results of this study support the existence of some commonalities in the HPT inactivation mechanism of C. botulinum type E spores and Bacillus spores although both organisms have significantly different HPT resistance properties. The information presented here contributes to closing the gap in knowledge regarding the HPT inactivation of spore formers relevant to food safety and may help industrial implementation of HPT processing. The markedly lower HPT resistance of C. botulinum type E spores compared with the resistance of spores from other C. botulinum types could allow for the implementation of milder processes without endangering food safety.

An atypical outbreak of food-borne botulism due to Clostridium botulinum types B and E from ham

An outbreak of human botulism was due to consumption of ham containing botulinum neurotoxins B and E. A Clostridium botulinum type E strain isolated from ham was assigned to a new subtype (E12) based on bont/E gene sequencing and belongs to a new multilocus sequence subtype, as analyzed by whole-genome sequencing.

Bacterial zoonoses of fishes: a review and appraisal of evidence for linkages between fish and human infections

Human contact with and consumption of fishes presents hazards from a range of bacterial zoonotic infections. Whereas many bacterial pathogens have been presented as fish-borne zoonoses on the basis of epidemiological and phenotypic evidence, genetic identity between fish and human isolates is not frequently examined or does not provide support for transmission between these hosts. In order to accurately assess the zoonotic risk from exposure to fishes in the context of aquaculture, wild fisheries and ornamental aquaria, it is important to critically examine evidence of linkages between bacteria infecting fishes and humans. This article reviews bacteria typically presented as fish-borne zoonoses, and examines the current strength of evidence for this classification. Of bacteria generally described as fish-borne zoonoses, only Mycobacterium spp., Streptococcus iniae, Clostridium botulinum, and Vibrio vulnificus appear to be well-supported as zoonoses in the strict sense. Erysipelothrix rhusiopathiae, while transmissible from fishes to humans, does not cause disease in fishes and is therefore excluded from the list. Some epidemiological and/or molecular linkages have been made between other bacteria infecting both fishes and humans, but more work is needed to elucidate routes of transmission and the identity of these pathogens in their respective hosts at the genomic level.

Effect of sporulation medium and its divalent cation content on the heat and high pressure resistance of Clostridium botulinum type E spores

Clostridium (C.) botulinum type E belongs to the non-proteolytic physiological C. botulinum group II and produces the highly potent Botulinum neurotoxin E (BoNT/E) even at refrigerated temperatures. As C. botulinum type E spores are highly prevalent in aquatic environments, seafood and fishery products are commonly associated with this organism. Hydrostatic high pressure (HHP) treatments, or treatments combining HHP with elevated temperatures (HHPT), can be used to improve traditional preservation methods and increase food safety, quality and durability. In this study, we assessed the effect of different sporulation media and cation concentration on the heat resistance, HHP resistance, and HHPT resistance of spores from three C. botulinum type E strains. SFE (sediment fish extract) sporulation media yielded the most resistant spores, whereas, in M140 media, the least resistant spores were produced. Furthermore our results indicate that the divalent cation content (Ca(2+), Mg(2+) and Mn(2+)) plays a role in the differential development of C. botulinum type E spore resistance to heat, HHP and HHPT in different media. Calcium cations confer heat and HPPT resistance to spores, while high amounts of magnesium cations appear to have a negative effect. Manganese cations in low concentrations are important for the development resistance to HPP and HPPT treatments, but not heat alone. This study provides valuable information on the nature of non-proteolytic C. botulinum type E spores grown in different media. The data provided here can be useful to the food industry and to researchers when considering spore properties in food safety risk assessment and the experimental design of future inactivation studies.

Genomic and physiological variability within Group II (non-proteolytic) Clostridium botulinum

Background

Clostridium botulinum is a group of four physiologically and phylogenetically distinct bacteria that produce botulinum neurotoxin. While studies have characterised variability between strains of Group I (proteolytic) C. botulinum, the genetic and physiological variability and relationships between strains within Group II (non-proteolytic) C. botulinum are not well understood. In this study the genome of Group II strain C. botulinum Eklund 17B (NRP) was sequenced and used to construct a whole genome DNA microarray. This was used in a comparative genomic indexing study to compare the relatedness of 43 strains of Group II C. botulinum (14 type B, 24 type E and 5 type F). These results were compared with characteristics determined from physiological tests.

Results

Whole genome indexing showed that strains of Group II C. botulinum isolated from a wide variety of environments over more than 75 years clustered together indicating the genetic background of Group II C. botulinum is stable. Further analysis showed that strains forming type B or type F toxin are closely related with only toxin cluster genes targets being unique to either type. Strains producing type E toxin formed a separate subset. Carbohydrate fermentation tests supported the observation that type B and F strains form a separate subset to type E strains. All the type F strains and most of type B strains produced acid from amylopectin, amylose and glycogen whereas type E strains did not. However, these two subsets did not differ strongly in minimum growth temperature or maximum NaCl concentration for growth. No relationship was found between tellurite resistance and toxin type despite all the tested type B and type F strains carrying tehB, while the sequence was absent or diverged in all type E strains.

Conclusions

Although Group II C. botulinum form a tight genetic group, genomic and physiological analysis indicates there are two distinct subsets within this group. All type B strains and type F strains are in one subset and all type E strains in the other.

Plasmid-borne type E neurotoxin gene clusters in Clostridium botulinum strains

A collection of 36 Clostridium botulinum type E strains was examined by pulsed-field gel electrophoresis (PFGE) and Southern hybridization with probes targeted to botE and orfX1 in the neurotoxin gene cluster. Three strains were found to contain neurotoxin subtype E1 gene clusters in large plasmids of about 146 kb in size.

Multi-locus variable number tandem repeat analysis for Clostridium botulinum type B isolates in Japan: comparison with other isolates and genotyping methods

Clostridium botulinum produces botulinum neurotoxin (BoNT) and causes botulism in humans and animals. Recently, 15-loci multi-locus variable number tandem repeat analysis (MLVA) for C. botulinum was developed for high-resolution and inter-lab comparative genotyping. This study examines the relation between MLVA and other genotyping methods such as pulsed-field gel electrophoresis (PFGE), multi-locus sequence typing (MLST), BoNT/B subtyping and bont/b gene location to evaluate MLVA as a method applicable to the genetic markers for C. botulinum type B. Japanese isolates were genotyped using MLVA and were compared with strains from other sources reported previously. Results show that the discriminatory power of MLVA was comparable to that of PFGE and higher than that of MLST. The topology of the minimum spanning tree (MST) constructed using MLVA data was very consistent with the phylogenetic classifications of PFGE and MLST. The MST topology also represented genetic diversity between the strains possessing bont/b gene on chromosomes and plasmids. Some Japanese isolates including those associated with infant botulism were inferred to be related to isolates of Europe origin from MLVA genotyping results. The MLVA scheme used for this study is apparently useful not only for high-resolution molecular typing, but also for phylogenetic characterization of C. botulinum type B.

Growth of group II Clostridium botulinum strains at extreme temperatures

The minimum and maximum growth temperatures and the maximum growth rates at 10, 30, 37, and 40°C were determined for 24 group II Clostridium botulinum strains. Genetic diversity of the strains was revealed by amplified fragment length polymorphism (AFLP) analysis. The minimum growth temperatures ranged from 6.2 to 8.6°C, and the maximum growth temperatures ranged from 34.7 to 39.9°C. The mean maximum growth temperatures and mean maximum growth rates of type E strains at 37°C were significantly higher than those of type B and type F strains. A significant correlation between maximum growth rates at 37°C and maximum growth temperatures was found for all strains. Some type E strains with a high minimum growth temperature also had a higher maximum growth rate at 37°C than at 30°C, which suggests that some group II C. botulinum strains are more mesophilic in their growth properties than others. We found relatively small differences between AFLP clusters, indicating that diverse genetic background among the strains was not reflected in the growth properties. The growth characteristics of group II C. botulinum and some type E strains with mesophilic growth properties may have an impact on inoculation studies and predictive modeling for assessing the safety of foods.

Clostridium botulinum group I strain genotyping by 15-locus multilocus variable-number tandem-repeat analysis

Clostridium botulinum is a taxonomic designation that encompasses a broad variety of spore-forming, Gram-positive bacteria producing the botulinum neurotoxin (BoNT). C. botulinum is the etiologic agent of botulism, a rare but severe neuroparalytic disease. Fine-resolution genetic characterization of C. botulinum isolates of any BoNT type is relevant for both epidemiological studies and forensic microbiology. A 10-locus multiple-locus variable-number tandem-repeat analysis (MLVA) was previously applied to isolates of C. botulinum type A. The present study includes five additional loci designed to better address proteolytic B and F serotypes. We investigated 79 C. botulinum group I strains isolated from human and food samples in several European countries, including types A (28), B (36), AB (4), and F (11) strains, and 5 nontoxic Clostridium sporogenes. Additional data were deduced from in silico analysis of 10 available fully sequenced genomes. This 15-locus MLVA (MLVA-15) scheme identified 86 distinct genotypes that clustered consistently with the results of amplified fragment length polymorphism (AFLP) and MLVA genotyping in previous reports. An MLVA-7 scheme, a subset of the MLVA-15, performed on a lab-on-a-chip device using a nonfluorescent subset of primers, is also proposed as a first-line assay. The phylogenetic grouping obtained with the MLVA-7 does not differ significantly from that generated by the MLVA-15. To our knowledge, this report is the first to analyze genetic variability among all of the C. botulinum group I serotypes by MLVA. Our data provide new insights into the genetic variability of group I C. botulinum isolates worldwide and demonstrate that this group is genetically highly diverse.

Analysis of Clostridium botulinum serotype E strains by using multilocus sequence typing, amplified fragment length polymorphism, variable-number tandem-repeat analysis, and botulinum neurotoxin gene sequencing

A total of 41 Clostridium botulinum serotype E strains from different geographic regions, including Canada, Denmark, Finland, France, Greenland, Japan, and the United States, were compared by multilocus sequence typing (MLST), amplified fragment length polymorphism (AFLP) analysis, variable-number tandem-repeat (VNTR) analysis, and botulinum neurotoxin (bont) E gene sequencing. The strains, representing environmental, food-borne, and infant botulism samples collected from 1932 to 2007, were analyzed to compare serotype E strains from different geographic regions and types of botulism and to determine whether each of the strains contained the transposon-associated recombinase rarA, involved with bont/E insertion. MLST examination using 15 genes clustered the strains into several clades, with most members within a cluster sharing the same BoNT/E subtype (BoNT/E1, E2, E3, or E6). Sequencing of the bont/E gene identified two new variants (E7, E8) that showed regions of recombination with other E subtypes. The AFLP dendrogram clustered the 41 strains similarly to the MLST dendrogram. Strains that could not be differentiated by AFLP, MLST, or bont gene sequencing were further examined using three VNTR regions. Both intact and split rarA genes were amplified by PCR in each of the strains, and their identities were confirmed in 11 strains by amplicon sequencing. The findings suggest that (i) the C. botulinum serotype E strains result from the targeted insertion of the bont/E gene into genetically conserved bacteria and (ii) recombination events (not random mutations) within bont/E result in toxin variants or subtypes within strains.

Biodiversity of Clostridium botulinum type E associated with a large outbreak of botulism in wildlife from Lake Erie and Lake Ontario

The genetic relatedness of Clostridium botulinum type E isolates associated with an outbreak of wildlife botulism was studied using random amplification of polymorphic DNA (RAPD). Specimens were collected from November 2000 to December 2008 during a large outbreak of botulism affecting birds and fish living in and around Lake Erie and Lake Ontario. In our present study, a total of 355 wildlife samples were tested for the presence of botulinum toxin and/or organisms. Type E botulinum toxin was detected in 110 samples from birds, 12 samples from fish, and 2 samples from mammals. Sediment samples from Lake Erie were also examined for the presence of C. botulinum. Fifteen of 17 sediment samples were positive for the presence of C. botulinum type E. Eighty-one C. botulinum isolates were obtained from plants, animals, and sediments; of these isolates, 44 C. botulinum isolates produced type E toxin, as determined by mouse bioassay, while the remaining 37 isolates were not toxic for mice. All toxin-producing isolates were typed by RAPD; that analysis showed 12 different RAPD types and multiple subtypes. Our study thus demonstrates that multiple genetically distinct strains of C. botulinum were involved in the present outbreak of wildlife botulism. We found that C. botulinum type E is present in the sediments of Lake Erie and that a large range of bird and fish species is affected.

Development and application of a new method for specific and sensitive enumeration of spores of nonproteolytic Clostridium botulinum types B, E, and F in foods and food materials

The highly potent botulinum neurotoxins are responsible for botulism, a severe neuroparalytic disease. Strains of nonproteolytic Clostridium botulinum form neurotoxins of types B, E, and F and are the main hazard associated with minimally heated refrigerated foods. Recent developments in quantitative microbiological risk assessment (QMRA) and food safety objectives (FSO) have made food safety more quantitative and include, as inputs, probability distributions for the contamination of food materials and foods. A new method that combines a selective enrichment culture with multiplex PCR has been developed and validated to enumerate specifically the spores of nonproteolytic C. botulinum. Key features of this new method include the following: (i) it is specific for nonproteolytic C. botulinum (and does not detect proteolytic C. botulinum), (ii) the detection limit has been determined for each food tested (using carefully structured control samples), and (iii) a low detection limit has been achieved by the use of selective enrichment and large test samples. The method has been used to enumerate spores of nonproteolytic C. botulinum in 637 samples of 19 food materials included in pasta-based minimally heated refrigerated foods and in 7 complete foods. A total of 32 samples (5 egg pastas and 27 scallops) contained spores of nonproteolytic C. botulinum type B or F. The majority of samples contained <100 spores/kg, but one sample of scallops contained 444 spores/kg. Nonproteolytic C. botulinum type E was not detected. Importantly, for QMRA and FSO, the construction of probability distributions will enable the frequency of packs containing particular levels of contamination to be determined.

Freshwater suspended sediments and sewage are reservoirs for enterotoxin-positive Clostridium perfringens

The release of fecal pollution into surface waters may create environmental reservoirs of feces-derived microorganisms, including pathogens. Clostridium perfringens is a commonly used fecal indicator that represents a human pathogen. The pathogenicity of this bacterium is associated with its expression of multiple toxins; however, the prevalence of C. perfringens with various toxin genes in aquatic environments is not well characterized. In this study, C. perfringens spores were used to measure the distribution of fecal pollution associated with suspended sediments in the nearshore waters of Lake Michigan. Particle-associated C. perfringens levels were greatest adjacent to the Milwaukee harbor and diminished in the nearshore waters. Species-specific PCR and toxin gene profiles identified 174 isolates collected from the suspended sediments, surface water, and sewage influent as C. perfringens type A. Regardless of the isolation source, the beta2 and enterotoxin genes were common among isolates. The suspended sediments yielded the highest frequency of cpe-carrying C. perfringens (61%) compared to sewage (38%). Gene arrangement of enterotoxin was investigated using PCR to target known insertion sequences associated with this gene. Amplification products were detected in only 9 of 90 strains, which suggests there is greater variability in cpe gene arrangement than previously described. This work presents evidence that freshwater suspended sediments and sewage influent are reservoirs for potentially pathogenic cpe-carrying C. perfringens spores.

Group I Clostridium botulinum strains show significant variation in growth at low and high temperatures

The minimum and maximum growth temperatures of 23 group I Clostridium botulinum strains of the toxin types A, AB, B, and F were determined. Moreover, the maximum growth rates at 20, 37, and 42 degrees C of the same strains were recorded. The minimum growth temperatures varied from 12.8 to 16.5 degrees C, whereas the maximum growth temperatures showed even wider variation, from 40.9 to 48.0 degrees C. At 20 and 37 degrees C, a twofold difference in maximum growth rates between the slowest and the fastest growing strains was found; at 42 degrees C the difference was more than 30-fold. As expected, all strains grew significantly slower at 20 degrees C than at 37 degrees C. However, eight type B strains grew substantially faster at 42 degrees C than they did at 37 degrees C. These findings indicate that the optimum growth temperature for some group I C. botulinum type B strains is higher than the temperature of 37 degrees C that is generally accepted. A significant correlation between maximum growth rates at 42 degrees C and maximum growth temperatures was found for type B and F strains, whereas for type A strains no such correlation could be found. Strain variation was particularly high for the type B strains, reflecting the wide genetic diversity of this toxin type. The significant variation between strains of group I C. botulinum may have an impact on inoculation studies and predictive modeling when assessing the safety of foods.

Sequencing the botulinum neurotoxin gene and related genes in Clostridium botulinum type E strains reveals orfx3 and a novel type E neurotoxin subtype

Three Clostridium botulinum type E strains were sequenced for the botulinum neurotoxin (BoNT) gene cluster, and 11 type E strains, representing a wide biodiversity, were sequenced for the bont/E gene. The total length of the BoNT/E gene cluster was 12,908 bp, and a novel gene (partial) designated orfx3, together with the complete orfx2 gene, was identified in the three type E strains for the first time. Apart from orfx3, the structure and organization of the neurotoxin gene cluster of the three strains were identical to those of previously published ones. Only minor differences (</=3%) in the nucleotide sequences of the gene cluster components were observed among the three strains and the published BoNT/E-producing clostridia. The orfx3, orfx2, orfx1, and p47 gene sequences of the three type E strains shared homologies of 81%, 67 to 76%, 78 to 79%, and 79 to 85%, respectively, with published sequences for type A1 and A2 C. botulinum. Analysis of bont/E from the 14 type E strains and 19 previously published BoNT/E-producing clostridia revealed six neurotoxin subtypes, with a new distinct subtype consisting of three Finnish isolates alone. The amino acid sequence of the subtype E6 neurotoxin differed 3 to 6% from the other subtypes, suggesting that these subtype E6 neurotoxins may possess specific antigenic or functional properties.

Differentiation of group I and group II strains of Clostridium botulinum by focal plane array Fourier transform infrared spectroscopy

A method was developed for whole-organism fingerprinting of Clostridium botulinum isolates by focal plane array Fourier transform infrared (FPA-FTIR) spectroscopy. A database of 150,000 infrared spectra of 44 strains of C. botulinum was acquired using a FPA-FTIR imaging spectrometer equipped with a 16 x 16 array detector to evaluate the ability of FTIR spectroscopy to differentiate the 44 strains. The database contained strains from C. botulinum groups I and II producing botulinum neurotoxin of serotypes A, B, E, and F. All strains were grown on each of three agar media (brain heart infusion, McClung Toabe agar base, and universal) prior to spectral acquisition. Given the dependence of the infrared spectra of microorganisms on the composition of the growth medium, the spectra were initially separated into three subsets corresponding to the three growth media employed. However, the replicate spectra of all strains, regardless of growth medium, were properly clustered by hierarchical cluster analysis based on differences in their infrared spectral profiles in three narrow spectral regions (1,428 to 1,412, 1,296 to 1,284, and 1,112 to 1,100 cm(-1)). The dendrogram generated from the FTIR data revealed complete separation between group I and group II strains. The spectral differences between group I and group II strains allowed accurate classification of C. botulinum strains at the group level in two blind validation studies (n = 40). These results demonstrate that FPA-FTIR spectroscopy has the potential for rapid discrimination of group I and group II C. botulinum strains in less than 3 min per sample.

Identification of Clostridium species and DNA fingerprinting of Clostridium perfringens by amplified fragment length polymorphism analysis

An amplified fragment length polymorphism (AFLP) method was applied to 129 strains representing 24 different Clostridium species, with special emphasis on pathogenic clostridia of medical or veterinary interest, to assess the potential of AFLP for identification of clostridia. In addition, the ability of the same AFLP protocol to type clostridia at the strain level was assessed by focusing on Clostridium perfringens strains. All strains were typeable by AFLP, so the method seemed to overcome the problem of extracellular DNase production. AFLP differentiated all Clostridium species tested, except for Clostridium ramosum and Clostridium limosum, which clustered together with a 45% similarity level. Other Clostridium species were divided into species-specific clusters or occupied separate positions. Wide genetic diversity was observed among Clostridium botulinum strains, which were divided into seven species-specific clusters. The same AFLP protocol was also suitable for typing C. perfringens at the strain level. A total of 29 different AFLP types were identified for 37 strains of C. perfringens; strains initially originating from the same isolate showed identical fingerprinting patterns and were distinguished from unrelated strains. AFLP proved to be a highly reproducible, easy-to-perform, and relatively fast method which enables high throughput of samples and can serve in the generation of identification libraries. These results indicate that the AFLP method provides a promising tool for the identification and characterization of Clostridium species.

Comparison of DNA fingerprinting methods for use in investigation of type E botulism outbreaks in the Canadian Arctic

Pulsed-field gel electrophoresis (PFGE), randomly amplified polymorphic DNA (RAPD) analysis, and automated ribotyping were compared for epidemiological typing of Clostridium botulinum type E using clinical and food isolates associated with four botulism outbreaks occurring in the Canadian Arctic. All type E strains previously untypeable by PFGE, even with the use of a formaldehyde fixation step, could be typed by the addition of 50 microM thiourea to the electrophoresis running buffer. Digestion with SmaI or XhoI followed by PFGE was used to link food and clinical isolates from four different type E botulism outbreaks and differentiate them from among 39 group II strains. Strain differentiation was unsuccessful with the automated ribotyping system, producing a single characteristic EcoRI fingerprint common to all group II strains. RAPD analysis of C. botulinum group II strains was not consistently reproducible with primer OPJ-6 or OPJ-13, apparently discriminating between epidemiologically related strains. A modified PFGE protocol was judged to be the most useful method for typing epidemiologically related C. botulinum type E strains, based on its ability to type all strains reproducibly and with an adequate level of discrimination.

Molecular subtyping of poultry-associated type A Clostridium perfringens isolates by repetitive-element PCR

Clostridium perfringens strains (type A) isolated from an integrated poultry operation were subtyped using repetitive-element PCR with Dt primers. Isolates were obtained from fecal, egg shell, fluff, and carcass rinse samples as part of a previously reported temporally linked epidemiological survey. A total of 48 isolates of C. perfringens were obtained from different stages of the broiler chicken production chain from two separate breeder farms that supplied a single hatchery that in turn provided chicks to a single grow-out farm whose flocks were processed at a single plant. All 48 isolates were typeable (100% typeability) by repetitive-element PCR with Dt primers. This subtyping method was highly reproducible and discriminatory. By repetitive-element PCR with Dt primers, isolates were classified into four major branches with 12 subgroups or clades. The Simpson's index of discrimination was calculated to be 0.96 for groupings of >95% correlation. Toxin gene profiles of the isolates indicated that all of the isolates were C. perfringens alpha-toxin gene positive and 46 of 48 isolates were beta2-toxin gene positive. All strains were negative for beta- and epsilon-toxin genes. Repetitive sequence-based PCR was found to be a technically practical and reproducible means of subtyping C. perfringens libraries from specific epidemiological or production environment settings.

The prevalence of Clostridium botulinum in European river lamprey (Lampetra fluviatilis) in Finland

The prevalence of Clostridium botulinum types A, B, E and F in river lampreys caught in Finnish rivers was determined for the first time using a quantitative PCR-MPN (most probable number) analysis. One of 67 raw whole lampreys (1.5%) was positive for the botulinum neurotoxin type E gene, with the estimated C. botulinum count being 100spores/kg. Two type E strains were isolated from the positive sample and confirmed as different genotypes by pulsed-field gel electrophoresis. Although the current procedure of bringing the charcoal-broiled lampreys to market has been without any further packaging or extended storage, interest towards increasing the shelf life of the product by vacuum-packaging is increasing. Our results demonstrate that C. botulinum type E may constitute a safety hazard in processed lampreys from the Baltic Sea area if packaging and extended shelf lives are to be used. To control the potential risk, a storage temperature of 3 degrees C or below should be recommended for these products.

Hazard and control of group II (non-proteolytic) Clostridium botulinum in modern food processing

Group II (non-proteolytic) Clostridium botulinum poses a safety hazard in modern food processing, which consists of mild pasteurization treatments, anaerobic packaging, extended shelf lives and chilled storage. The high risk is reflected in the relatively large number of botulism cases due to group II C. botulinum in commercially produced foods during the past decades. Because of the high prevalence of group II C. botulinum in the environment, food raw materials may carry spores. Although group II spores are less heat-resistant than group I (proteolytic) spores, they can tolerate the heat treatments employed in the chilled food industry. Some food components may actually provide spores with protection from heat. Spore heat resistance should therefore be investigated for each food in order to determine the efficiency of industrial heat treatments. Group II strains are psychrotrophic and thus they are able to grow at refrigeration temperatures. Anaerobic packages and extended shelf lives provide C. botulinum with favourable conditions for growth and toxin formation. As the use of salt and other preservatives in these foods is limited, microbiological safety relies mainly on refrigerated storage. This sets great challenges on the production of chilled packaged foods. To ensure the safety of these foods, more than one factor should safeguard against botulinal growth and toxin production.

A new scaleable method for the purification of botulinum neurotoxin type E

Botulinum neurotoxins belong to the most toxic substances in nature. Well-known as a food poisoning agent for almost two centuries, the beneficial aspects of this bacterial metabolite were rediscovered about 30 years ago. These toxins, which are produced by the anaerobic bacterium Clostridium botulinum are nowadays used to treat a variety of neuro-muscular disorders. The increased demand requires techniques for the production and purification of these toxins on an industrial scale. The method described herein is based on filtration and chromatography procedures only. Precipitation, centrifugation and dialysis steps were consequently excluded to develop a protocol, which can easily be scaled up from the laboratory purification to industrial needs. About 4 mg of BoNT/E were purified from a 10-L batch culture corresponding to an overall recovery of approximately 14%.

Proteolytic Clostridium botulinum type B in the gastric content of a patient with type E botulism due to whitefish eggs

Whitefish eggs were confirmed by pulsed-field gel electrophoresis to cause type E foodborne botulism in a 54-year-old patient in Finland. Botulinum neurotoxin and/or nonproteolytic Clostridium botulinum type E organisms were detected in fecal and gastric samples from the patient and in suspected whitefish eggs. Apart from C. botulinum type E, proteolytic type B organisms were detected in the patient's gastric content. This was considered to be insignificant with respect to the clinical disease, suggesting botulinal spores to be occasionally present in the human gastrointestinal tract without any apparent clinical significance. This is the first domestic case of foodborne botulism in Finland.

Botulismus durch Räucherlachsverzehr

Fresh fish products are exquisitely prone to be the source for food botulism because of primary contamination with Clostridium botulinum spores, lack of heat inactivation of C. botulinum spores, frequently used air-tight packaging, lack of preservatives, lack of heat inactivation of already produced botulinum toxin and because of substantial low temperature resistance of C. botulinum type E typically found in fish botulism. We can reporting a 25-year-old patient with food botulism presenting with an anticholinergic syndrome with mydriasis, accommodation difficulties, dryness of mouth, reduced sweating, constipation and reduced heart rate variance and only discrete involvement of striate muscles with ptosis, diplopia and generalised fatigue, all of which developed 12 h after the consumption of airtight sealed smoked salmon. The salmon was consumed 3 days after the 'use by' date had expired.

Characterization of Clostridium botulinum strains associated with an infant botulism case in the United Kingdom

The sixth case of infant botulism in the United Kingdom was reported in 2001. The case was caused by a type B strain of Clostridium botulinum. Strains of C. botulinum were isolated from the baby's feces and from foodstuffs in the household in an attempt to document transmission. The aims of this study were to characterize the strains of C. botulinum associated with the botulism case. This was performed using a variety of techniques, including C. botulinum culture phenotypic properties, neurotoxin characterization, and pulsed-field gel electrophoresis (PFGE) banding patterns. Cultures associated with this case as well as isolates from stored and historical samples were analyzed and compared. C. botulinum type B PFGE patterns from the infant and from an opened container of infant formula were indistinguishable, while the PFGE profile of a strain presumably isolated from an unopened archival container was unique. The results suggest that the unopened brand of formula was not the source for transmission of spores to the infant and that the strain was distinct from previous botulism cases in the United Kingdom. Since environmental testing was not performed, it is not possible to deduce other sources of transmission.

Diversity of proteolytic Clostridium botulinum strains, determined by a pulsed-field gel electrophoresis approach

Pulsed-field gel electrophoresis (PFGE) was applied to the study of the similarity of 55 strains of proteolytic Clostridium botulinum (C. botulinum group I) types A, AB, B, and F. Rare-cutting restriction enzymes ApaI, AscI, MluI, NruI, PmeI, RsrII, SacII, SmaI, and XhoI were tested for their suitability for the cleavage of DNA of five proteolytic C. botulinum strains. Of these enzymes, SacII, followed by SmaI and XhoI, produced the most convenient number of fragments for genetic typing and were selected for analysis of the 55 strains. The proteolytic C. botulinum species was found to be heterogeneous. In the majority of cases, PFGE enabled discrimination between individual strains of proteolytic C. botulinum types A and B. The different toxin types were discriminated at an 86% similarity level with both SacII and SmaI and at an 83% similarity level with XhoI. Despite the high heterogeneity, three clusters at a 95% similarity level consisting of more than three strains of different origin were noted. The strains of types A and B showed higher diversity than the type F organisms which formed a single cluster. According to this survey, PFGE is to be considered a useful tool for molecular epidemiological analysis of proteolytic C. botulinum types A and B. However, epidemiological conclusions based on PFGE data only should be made with discretion, since highly similar PFGE patterns were noticed, especially within the type B strains.

Efficient DNA fingerprinting of Clostridium botulinum types A, B, E, and F by amplified fragment length polymorphism analysis

Amplified fragment length polymorphism (AFLP) analysis was applied to characterize 33 group I and 37 group II Clostridium botulinum strains. Four restriction enzyme and 30 primer combinations were screened to tailor the AFLP technique for optimal characterization of C. botulinum. The enzyme combination HindIII and HpyCH4IV, with primers having one selective nucleotide apiece (Hind-C and Hpy-A), was selected. AFLP clearly differentiated between C. botulinum groups I and II; group-specific clusters showed <10% similarity between proteolytic and nonproteolytic C. botulinum strains. In addition, group-specific fragments were detected in both groups. All strains studied were typeable by AFLP, and a total of 42 AFLP types were identified. Extensive diversity was observed among strains of C. botulinum type E, whereas group I had lower genetic biodiversity. These results indicate that AFLP is a fast, highly discriminating, and reproducible DNA fingerprinting method with excellent typeability, which, in addition to its suitability for typing at strain level, can be used for C. botulinum group identification.

Prevalence of Clostridium botulinum types B, E and F in faecal samples from Swedish cattle

Faeces were collected from 60 cows at three slaughterhouses situated in southern and central Sweden. The faecal samples were collected during two sampling periods over the year, summer and winter. All samples were analysed for the presence of Clostridium botulinum spores, according to a combined selection and enrichment PCR procedure. One PCR assay was specific for part of the type B neurotoxin gene, while the other assay was specific for both type E and F neurotoxin genes. The prevalence of C. botulinum in Swedish cattle was established to be 73% for non-proteolytic type B and less than 5% for types E and F. Twenty-eight (64%) of the positive faecal samples had a spore load of less than 4 spores/g. Statistical analysis (ANOVA) showed that seasonal variation (summer and winter) had a significant effect on the prevalence of C. botulinum type B in cattle, whereas the effect of geographical location of rearing of the cattle (southern and central Sweden) was less significant.

High prevalence of Clostridium botulinum types A and B in honey samples detected by polymerase chain reaction

A test protocol for reliable detection of Clostridium botulinum types A and B spores in honey by polymerase chain reaction (PCR) was developed and used for a prevalence survey of C. botulinum spores in 190 honey samples. The inhibiting effects of honey on microbial growth and PCR analysis were overcome by using a method of supernatant filtration (SF) in the preparation of the samples before enrichment and PCR. By using this method, an inoculum of 0.1 spore of C. botulinum/g honey could be detected. In the prevalence survey, spores of C. botulinum were detected in 8 (7%) of the 114 Finnish and in 12 (16%) of the 76 imported honey samples. The quantity of spores in PCR-positive samples varied from less than 18 to 140 spores/kg. Neurotoxin gene sequences corresponding to C. botulinum type A were detected in 17 samples and proteolytic type B in 12 samples by PCR analysis. Both types A and B were detected in nine samples. Strains of C. botulinum type A were isolated from 14 and type B from 2 of the 20 PCR-positive samples. This is the first report of type A spores of C. botulinum being detected and isolated in Fennoscandia.

Clostridium botulinum and its neurotoxins: a metabolic and cellular perspective

Clostridium botulinum comprises a diverse assemblage of clostridia that have the common property of producing a distinctive protein neurotoxin (BoNT) of similar pharmacological activity and extraordinary potency. BoNTs are produced in culture as molecular complexes consisting of BoNT, hemagglutinin (HA) and associated subcomponent proteins, nontoxic nonhemagglutinin (NTNH), and RNA. The genes encoding the protein components reside as a cluster on the chromosome, on bacteriophages, or on plasmids depending on the C. botulinum serotype. A gene BotR coding for a regulatory protein has been detected in toxin gene clusters from certain strains, as well as ORFs coding for uncharacterized components. The gene encoding TeNT is located on a large plasmid, and expression of the structural gene is controlled by the regulatory gene, TetR, located immediately upstream of the TeNT structural gene. TeNT is not known to be assembled into a protein/nucleic acid complex in culture. Cellular synthesis of BoNT and TeNT have been demonstrated to be positively regulated by the homologous proteins, BotR/A and TetR. Evidence suggests that negative regulatory factors and general control cascades such as those involved in nitrogen regulation and carbon catabolite repression also regulate synthesis of BoNTs. Neurotoxigenic clostridia have attracted considerable attention from scientists and clinicians during the past decade, and many excellent reviews are available on various aspects of these organisms and their neurotoxins. However, certain areas have not been well-studied, including metabolic regulation of toxin formation and genetic tools to study neurotoxigenic clostridia. These topics are the focus of this review.

Development of a combined selection and enrichment PCR procedure for Clostridium botulinum Types B, E, and F and its use to determine prevalence in fecal samples from slaughtered pigs

A specific and sensitive combined selection and enrichment PCR procedure was developed for the detection of Clostridium botulinum types B, E, and F in fecal samples from slaughtered pigs. Two enrichment PCR assays, using the DNA polymerase rTth, were constructed. One assay was specific for the type B neurotoxin gene, and the other assay was specific for the type E and F neurotoxin genes. Based on examination of 29 strains of C. botulinum, 16 strains of other Clostridium spp., and 48 non-Clostridium strains, it was concluded that the two PCR assays detect C. botulinum types B, E, and F specifically. Sample preparation prior to the PCR was based on heat treatment of feces homogenate at 70 degrees C for 10 min, enrichment in tryptone-peptone-glucose-yeast extract broth at 30 degrees C for 18 h, and DNA extraction. The detection limits after sample preparation were established as being 10 spores per g of fecal sample for nonproteolytic type B, and 3.0 x 10(3) spores per g of fecal sample for type E and nonproteolytic type F with a detection probability of 95%. Seventy-eight pig fecal samples collected from slaughter houses were analyzed according to the combined selection and enrichment PCR procedure, and 62% were found to be PCR positive with respect to the type B neurotoxin gene. No samples were positive regarding the type E and F neurotoxin genes, indicating a prevalence of less than 1.3%. Thirty-four (71%) of the positive fecal samples had a spore load of less than 4 spores per g. Statistical analysis showed that both rearing conditions (outdoors and indoors) and seasonal variation (summer and winter) had significant effects on the prevalence of C. botulinum type B, whereas the effects of geographical location (southern and central Sweden) were less significant.

Genetic analysis of type E botulinum toxin-producing Clostridium butyricum strains

Type E botulinum toxin (BoNT/E)-producing Clostridium butyricum strains isolated from botulism cases or soil specimens in Italy and China were analyzed by using nucleotide sequencing of the bont/E gene, random amplified polymorphic DNA (RAPD) assay, pulsed-field gel electrophoresis (PFGE), and Southern blot hybridization for the bont/E gene. Nucleotide sequences of the bont/E genes of 11 Chinese isolates and of the Italian strain BL 6340 were determined. The nucleotide sequences of the bont/E genes of 11 C. butyricum isolates from China were identical. The deduced amino acid sequence of BoNT/E from the Chinese isolates showed 95.0 and 96.9% identity with those of BoNT/E from C. butyricum BL 6340 and Clostridium botulinum type E, respectively. The BoNT/E-producing C. butyricum strains were divided into the following three clusters based on the results of RAPD assay, PFGE profiles of genomic DNA digested with SmaI or XhoI, and Southern blot hybridization: strains associated with infant botulism in Italy, strains associated with food-borne botulism in China, and isolates from soil specimens of the Weishan lake area in China. A DNA probe for the bont/E gene hybridized with the nondigested chromosomal DNA of all toxigenic strains tested, indicating chromosomal localization of the bont/E gene in C. butyricum. The present results suggest that BoNT/E-producing C. butyricum is clonally distributed over a vast area.

Safety evaluation of sous vide-processed products with respect to nonproteolytic Clostridium botulinum by use of challenge studies and predictive microbiological models

Sixteen different types of sous vide-processed products were evaluated for safety with respect to nonproteolytic group II Clostridium botulinum by using challenge tests with low (2. 0-log-CFU/kg) and high (5.3-log-CFU/kg) inocula and two currently available predictive microbiological models, Food MicroModel (FMM) and Pathogen Modeling Program (PMP). After thermal processing, the products were stored at 4 and 8 degrees C and examined for the presence of botulinal spores and neurotoxin on the sell-by date and 7 days after the sell-by date. Most of the thermal processes were found to be inadequate for eliminating spores, even in low-inoculum samples. Only 2 of the 16 products were found to be negative for botulinal spores and neurotoxin at both sampling times. Two products at the high inoculum level showed toxigenesis during storage at 8 degrees C, one of them at the sell-by date. The predictions generated by both the FMM thermal death model and the FMM and PMP growth models were found to be inconsistent with the observed results in a majority of the challenges. The inaccurate predictions were caused by the limited number and range of the controlling factors in the models. Based on this study, it was concluded that the safety of sous vide products needs to be carefully evaluated product by product. Time-temperature combinations used in thermal treatments should be reevaluated to increase the efficiency of processing, and the use of additional antibotulinal hurdles, such as biopreservatives, should be assessed.