Characterization of Campylobacter spp. isolated from wild birds in the Antarctic and Sub-Antarctic.

A lack of knowledge of naturally occurring pathogens is limiting our ability to use the Antarctic to study the impact human-mediated introduction of infectious microorganisms have on this relatively uncontaminated environment. As no large-scale coordinated effort to remedy this lack of knowledge has taken place, we rely on smaller targeted efforts to both study present microorganisms and monitor the environment for introductions. In one such effort, we isolated Campylobacter species from fecal samples collected from wild birds in the Antarctic Peninsula and the sub-Antarctic island of South Georgia. Indeed, in South Georgia, we found Campylobacter lari and the closely related Campylobacter peloridis, but also distantly related human-associated multilocus sequence types of Campylobacter jejuni. In contrast, in the Antarctic Peninsula, we found C. lari and two closely related species, Campylobacter subantarcticus and Campylobacter volucris, but no signs of human introduction. In fact, our finding of human-associated sequence types of C. jejuni in South Georgia, but not in the Antarctic Peninsula, suggests that efforts to limit the spread of infectious microorganisms to the Antarctic have so far been successful in preventing the introduction of C. jejuni. However, we do not know how it came to South Georgia and whether the same mode of introduction could spread it from there to the Antarctic Peninsula.

Using whole genome sequencing to study American foulbrood epidemiology in honeybees.

American foulbrood (AFB), caused by Paenibacillus larvae, is a devastating disease in honeybees. In most countries, the disease is controlled through compulsory burning of symptomatic colonies causing major economic losses in apiculture. The pathogen is endemic to honeybees world-wide and is readily transmitted via the movement of hive equipment or bees. Molecular epidemiology of AFB currently largely relies on placing isolates in one of four ERIC-genotypes. However, a more powerful alternative is multi-locus sequence typing (MLST) using whole-genome sequencing (WGS), which allows for high-resolution studies of disease outbreaks. To evaluate WGS as a tool for AFB-epidemiology, we applied core genome MLST (cgMLST) on isolates from a recent outbreak of AFB in Sweden. The high resolution of the cgMLST allowed different bacterial clones involved in the disease outbreak to be identified and to trace the source of infection. The source was found to be a beekeeper who had sold bees to two other beekeepers, proving the epidemiological link between them. No such conclusion could have been made using conventional MLST or ERIC-typing. This is the first time that WGS has been used to study the epidemiology of AFB. The results show that the technique is very powerful for high-resolution tracing of AFB-outbreaks.

Outbreak of Campylobacteriosis Following a Dairy Farm Visit: Confirmation by Genotyping.

In April-May 2014, an outbreak of campylobacteriosis occurred after a preschool visit to a dairy farm in the South Western part of Sweden. During the visit, a meal, including unpasteurized milk, was served. A retrospective cohort study using a web-based questionnaire was performed among the participants (n = 30) of the farm visit. A total of 24 of the 30 (80%) cohort members completed the questionnaire. Eleven cases were identified, and Campylobacter jejuni was isolated from eight of them. Seven of the cases were 2- to 7-year-old children. We found the highest attack rates among those who usually drink milk (45%) and those who consumed unpasteurized milk during the farm visit (42%). No cases were unexposed (risk ratio incalculable). As result of the farm investigation, Campylobacter was isolated from cattle on the farm. Genotyping with pulsed-field gel electrophoresis and whole genome sequencing confirmed that human and cattle isolates of C. jejuni belonged to one cluster. Thus, cattle on the farm are considered the source of infection, and the most likely vehicle of transmission was contaminated unpasteurized milk. We recommend consumption of heat-treated milk only and increased awareness of the risk of consuming unpasteurized milk.

Transferable genes putatively conferring elevated minimum inhibitory concentrations of narasin in Enterococcus faecium from Swedish broilers.

The minimum inhibitory concentration (MIC) of the polyether ionophore antibiotic narasin is elevated in a large proportion of Enterococcus faecium from Swedish broilers. The aim of this study was to identify gene(s) responsible for these elevated MICs. Six plasmids, four conferring vancomycin resistance and elevated MIC of narasin and two only conferring resistance to vancomycin, were sequenced. The genes for a putative mechanism for elevated MIC of narasin was used to design a PCR assay which in turn was used to screen 100 isolates of E. faecium from Swedish broilers. A 5.9 kb area was only found in the plasmids transferring elevated MIC of narasin. This area included two genes coding for an ABC-type transporter; an 'ABC transporter permease protein' and an 'ABC-type multidrug transport system, ATPase component'. These genes are known to confer resistance to the ionophore tetronasin. PCR investigation confirmed a correlation between the presence of the genes and a MIC of narasin ≥ 2 mg/L. The results of this study indicate that the ABC permease together with the ABC ATPase are responsible for the elevated MIC of narasin present among E. faecium in Swedish broilers. To our knowledge, this is the first report of a putative transferable mechanism for elevated MIC of narasin.

Brucellosis outbreak in a Swedish kennel in 2013: determination of genetic markers for source tracing.

Brucellosis is a highly infectious zoonotic disease but rare in Sweden. Nonetheless, an outbreak of canine brucellosis caused by an infected dog imported to Sweden was verified in 2013. In total 25 dogs were tested at least duplicated by the following approaches: real-time PCR for the detection of Brucella canis, a Brucella genus-specific real-time PCR, selective cultivation, and microscopic examination. The whole genome of B. canis strain SVA13 was analysed regarding genetic markers for epidemiological examination. The genome of an intact prophage of Roseobacter was detected in B. canis strain SVA13 with whole genome sequence prophage analysis (WGS-PA). It was shown that the prophage gene content in the American, African and European isolates differs remarkably from the Asian strains. The prophage sequences in Brucella may therefore serve of use as genetic markers in epidemiological investigations. Phage DNA fragments were also detected in clustered, regularly interspaced short palindromic repeats (CRISPR) in the genome of strain SVA13. In addition to the recommendations for genetic markers in Brucella outbreak tracing, our paper reports a validated two-step stand-alone real-time PCR for the detection of B. canis and its first successful use in an outbreak investigation.

Whole-Genome Sequence of Brucella canis Strain SVA13, Isolated from an Infected Dog.

An outbreak of canine brucellosis in Sweden was confirmed by the National Veterinary Institute (SVA) in August 2013. The whole genome of the causative agent was sequenced, assembled, and analyzed.

Microevolution during an Anthrax outbreak leading to clonal heterogeneity and penicillin resistance.

Anthrax is a bacterial disease primarily affecting grazing animals but it can also cause severe disease in humans. We have used genomic epidemiology to study microevolution of the bacterium in a confined outbreak in cattle which involved emergence of an antibiotic-resistant phenotype. At the time of death, the animals contained a heterogeneous population of Single Nucleotide Variants (SNVs), some being clonal but most being subclonal. We found that independent isolates from the same carcass had similar levels of SNV differences as isolates from different animals. Furthermore the relative levels of subclonal populations were different in different locations in the same carcass. The heterogeneity appeared to be derived in part from heterogeneity in the infectious dose. The resistance phenotype was linked to clonal mutations in an anti-sigma factor gene and in one case was preceded by an acquisition of a hypermutator phenotype. In another animal, small subclonal populations were observed with counteracting mutations that had turned off the resistance genes. In summary, this study shows the importance of accounting for both acquired and inherited heterogeneity when doing high-resolution infection tracing and when estimating the risks associated with penicillin treatment.

In silico and in vitro evaluation of PCR-based assays for the detection of Bacillus anthracis chromosomal signature sequences.

Bacillus anthracis, the causative agent of anthrax, is a zoonotic pathogen that is relatively common throughout the world and may cause life threatening diseases in animals and humans. There are many PCR-based assays in use for the detection of B. anthracis. While most of the developed assays rely on unique markers present on virulence plasmids pXO1 and pXO2, relatively few assays incorporate chromosomal DNA markers due to the close relatedness of B. anthracis to the B. cereus group strains. For the detection of chromosomal DNA, different genes have been used, such as BA813, rpoB, gyrA, plcR, S-layer, and prophage-lambda. Following a review of the literature, an in silico analysis of all signature sequences reported for identification of B. anthracis was conducted. Published primer and probe sequences were compared for specificity against 134 available Bacillus spp. genomes. Although many of the chromosomal targets evaluated are claimed to be specific to B. anthracis, cross-reactions with closely related B. cereus and B. thuringiensis strains were often observed. Of the 35 investigated PCR assays, only 4 were 100% specific for the B. anthracis chromosome. An interlaboratory ring trial among five European laboratories was then performed to evaluate six assays, including the WHO recommended procedures, using a collection of 90 Bacillus strains. Three assays performed adequately, yielding no false positive or negative results. All three assays target chromosomal markers located within the lambdaBa03 prophage region (PL3, BA5345, and BA5357). Detection limit was further assessed for one of these highly specific assays.

Gegenees: fragmented alignment of multiple genomes for determining phylogenomic distances and genetic signatures unique for specified target groups.

The rapid development of Next Generation Sequencing technologies leads to the accumulation of huge amounts of sequencing data. The scientific community faces an enormous challenge in how to deal with this explosion. Here we present a software tool, 'Gegenees', that uses a fragmented alignment approach to facilitate the comparative analysis of hundreds of microbial genomes. The genomes are fragmented and compared, all against all, by a multithreaded BLAST control engine. Ready-made alignments can be complemented with new genomes without recalculating the existing data points. Gegenees gives a phylogenomic overview of the genomes and the alignment can then be mined for genomic regions with conservation patterns matching a defined target group and absent from a background group. The genomic regions are given biomarker scores forming a uniqueness signature that can be viewed and explored, graphically and in tabular form. A primer/probe alignment tool is also included for specificity verification of currently used or new primers. We exemplify the use of Gegenees on the Bacillus cereus group, on Foot and Mouth Disease Viruses, and on strains from the 2011 Escherichia coli O104:H4 outbreak. Gegenees contributes towards an increased capacity of fast and efficient data mining as more and more genomes become sequenced.

Towards an international standard for detection and typing botulinum neurotoxin-producing Clostridia types A, B, E and F in food, feed and environmental samples: a European ring trial study to evaluate a real-time PCR assay.

A real-time PCR method for detection and typing of BoNT-producing Clostridia types A, B, E, and F was developed on the framework of the European Research Project "Biotracer". A primary evaluation was carried out using 104 strains and 17 clinical and food samples linked to botulism cases. Results showed 100% relative accuracy, 100% relative sensitivity, 100% relative specificity, and 100% selectivity (inclusivity on 73 strains and exclusivity on 31 strains) of the real-time PCR against the reference cultural method combined with the standard mouse bioassay. Furthermore, a ring trial study performed at four different European laboratories in Italy, France, the Netherlands, and Sweden was carried out using 47 strains, and 30 clinical and food samples linked to botulism cases. Results showed a concordance of 95.7% among the four laboratories. The reproducibility generated a relative standard deviation in the range of 2.18% to 13.61%. Considering the high level of agreement achieved between the laboratories, this real-time PCR is a suitable method for rapid detection and typing of BoNT-producing Clostridia in clinical, food and environmental samples and thus support the use of it as an international standard method.

Accidental and deliberate microbiological contamination in the feed and food chains--how biotraceability may improve the response to bioterrorism.

A next frontier of the global food safety agenda has to consider a broad spectrum of bio-risks, such as accidental and intentional contaminations in the food and feed chain. In this article, the background for the research needs related to biotraceability and response to bioterrorism incidents are outlined. Given the current scale of international trade any response need to be considered in an international context. Biotraceability (e.g. the ability to use downstream information to point to processes or within a particular food chain that can be identified as the source of undesirable agents) is crucial in any food-born outbreak and particular in the response to bioterrorism events. In the later case, tested and proven biotraceability improves the following: (i) international collaboration of validated tracing tools and detection methods, (ii) multi-disciplinary expertise and collaboration in the field of food microbiology and conceptual modeling of the food chain, (iii) sampling as a key step in biotracing (iv) optimized sample preparation procedures, including laboratory work in Biosafety level 3 (BSL-3) laboratories, (v) biomarker discovery for relevant tracing and tracking applications, and (vi) high-throughput sequencing using bio-informatic platforms to speed up the characterization of the biological agent. By applying biotraceability, the response phase during a bioterrorism event may be shortened and is facilitated for tracing the origin of biological agent contamination.

Evaluation of Bacillus strains as model systems for the work on Bacillus anthracis spores.

Available strain collections of Bacillus anthracis and Bacillus cereus were screened for B. cereus strains sharing major genotypic characteristics with B. anthracis. Based on the comparison of partial spoIIIAB sequences, whole genome sequences and MLST, a strain set representing different lineages including candidate model strains for B. anthracis was compiled. Spores from the selected strain set and two B. anthracis strains were prepared according to a newly optimized protocol transferable to biosafety level-3 (BSL3) conditions and phenotypic characteristics including scanning electron microscopy (SEM), heat inactivation, and germination were evaluated. Two B. cereus isolates were identified that were genetically related to B. anthracis and showed high similarity to B. anthracis spores in their heat inactivation profile and their response to the germinants l-alanine and inosine. In addition, these isolates were also mimicking B. anthracis on modified PLET, a selective plating medium for B. anthracis, and shared various other biochemical characteristics with B. anthracis. Therefore these two strains are not only appropriate models for B. anthracis in experiments based on spore characteristics but also in trials working with plating media. These two strains are now used within the BIOTRACER consortium as validated models for B. anthracis and will facilitate the development and optimization of tracing and detection systems for B. anthracis in the food and feed chain.

A multiplex real-time PCR for identifying and differentiating B. anthracis virulent types.

Bacillus anthracis is closely related to the endospore forming bacteria Bacillus cereus and Bacillus thuringiensis. For accurate detection of the life threatening pathogen B. anthracis, it is essential to distinguish between these three species. Here we present a novel multiplex real-time PCR for simultaneous specific identification of B. anthracis and discrimination of different B. anthracis virulence types. Specific B. anthracis markers were selected by whole genome comparison and different sets of primers and probes with optimal characteristic for multiplex detection of the B. anthracis chromosome, the B. anthracis pXO1 and pXO2 plasmids and an internal control (IC) were designed. The primer sets were evaluated using a panel of B. anthracis strains and exclusivity was tested using genetically closely related B. cereus strains. The robustness of final primer design was evaluated by laboratories in three different countries using five different real-time PCR thermocyclers. Testing of a panel of more than 20 anthrax strains originating from different locations around the globe, including the recent Swedish anthrax outbreak strain, showed that all strains were detected correctly.