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Comparison of DRB sequence-based typing using different strategies.

Sequence-based typing (SBT) has become an important tool in the identification of HLA alleles. In this study a comparison was made between SBT of DRB1/3/4/5 alleles performed in two laboratories each using a different strategy for SBT. The laboratories in Utrecht and in Maastricht performed direct sequencing of PCR amplified genomic DNA from 30 selected samples. Primers and conditions for PCR amplification were different. Sequencing was either performed with T7 polymerase, using internal sequencing primers, or with cycle sequencing using an M13 tailed system. Two different automated DNA sequencers were used; the ALFexpress from Pharmacia and Applied Biosystems 373A. We concluded that nor the method of sequencing nor the sequencing machine influences typing results. However the PCR reaction used for generating template DNA is the most critical step. Different primers and different conditions can lead to false negative reactions. The fact that these false negative reactions can occur with different alleles in different combinations but not in all, implicates that extensive quality control is needed to assure correct typing results.

HLA-DR Antigens↗

Chromosomal localization and distribution of simple sequence repeats and the Arabidopsis-type telomere sequence in the genome of Cicer arietinum L.

We used fluorescence in situ hybridization to probe the physical organization of five simple sequence repeat motifs and the Arabidopsis-type telomeric repeat in metaphase chromosomes and interphase nuclei of chickpea (Cicer arietinum L.). Hybridization signals were observed with the whole set of probes and on all chromosomes, but the distribution and intensity of signals varied depending on the motif. On root-tip metaphase chromosomes, CA and GATA repeats were mainly restricted to centromeric areas, with additional GATA signals along some chromosomes. TA, A and AAC repeats were organized in a more dispersed manner, with centromeric regions being largely excluded. In interphase nuclei of the inner integument, CA and GATA signals predominantly occurred in the heterochromatic endochromocentres, whereas the other motifs were found both in eu- and heterochromatin. The distribution of the Arabidopsis-type telomeric repeat (TTTAGGG)n on metaphase chromosomes was found to be quite exceptional. One major cluster of repeats was spread along the short arm of chromosome B, whereas a second, weaker signal occurred interstitially on chromosome A. Only faint and inconsistent hybridization signals were visualized with the same probe at the chromosomal termini.

Arabidopsis↗

Spatial epidemiology and natural population structure of Campylobacter jejuni colonizing a farmland ecosystem.

Recent progress in determining the population structure of Campylobacter jejuni, and discerning associations between genotypes and specific niches, has emphasized the shortfall in our understanding of the ecology and epidemiology of this bacterium. We examined the natural structure of the C. jejuni community associated with cattle farmland in the UK by structured spatiotemporal sampling of habitats, including livestock and wild animal faeces, environmental water and soil, over a 10-week period within a 100 km2 area. A total of 172 isolates were characterized using multilocus sequence typing into 65 sequence types (STs). Isolates from cattle faeces were significantly over-represented in the ST-61 complex, whereas isolates from wildlife faeces and water were more likely to belong to the ST-45 complex and a number of unusual STs, many of which were first encountered during this study. Sampling within a narrow spatiotemporal window permitted the application of novel statistical methods exploring the relationship between the genetic relatedness and spatial separation of isolates. This approach showed that isolates from the same sampling squares and squares separated by <1.0 km were genetically more similar than isolates separated by greater distances. Our study demonstrates the potential of multilocus sequence typing combined with spatial modelling in exploring natural transmission pathways for C. jejuni.

Agriculture↗

Heterogeneity of methicillin-resistant Staphylococcus aureus strains at a German university hospital during a 1-year period.

Heterogeneous methicillin-resistant Staphylococcus aureus (MRSA) strains, including community-acquired MRSA strains, have been observed in Central Europe. The purpose of this study was to characterize by molecular methods MRSA isolated during the period 2002-2003 at the Otto-von-Guericke University Hospital in Magdeburg, Germany, and at a nearby chronic care facility. Strains were analyzed for their resistance phenotype. Selected isolates were typed by multilocus sequence typing (MLST), by a multiplex polymerase chain reaction (PCR) for the staphylococcal cassette chromosome mec (SCCmec), by an allele-specific PCR for the staphylococcal accessory gene regulator (agr), and by PCR for the presence of toxin genes (sea-sej, tsst-1, hlgA, C, and B, lukE/D, and luk-pvl). Of the 2,731 S. aureus isolates studied, 199 (7.3%) were MRSA, with a prevalence of 21.6%, 19.6%, and 12% in the department of dermatology, the chronic care facility, and the intensive care units. Six different sequence types (ST247, ST228, ST22, ST22a, ST225, and ST45) were observed. Of these, ST22, ST22a, and ST45 dominated (>50%) in the department of dermatology and the chronic care facility. Strains with these sequence types were usually not resistant to gentamicin and were associated with agr group I, the SCCmec type IV element, and the presence of the sec and sed toxin genes. ST228 strains were found mainly in the intensive care units and had a broader resistance phenotype and were associated with agr group II and the SCCmec type I element. All luk-pvl-positive MRSA isolates (n=8) belonged to agr group I and were typed as ST22 or ST45 and contained the SCCmec type I (n=1), type III (n=1), or type IV (n=6) element. The main observations of this study are in concordance with previously reported findings showing dissemination of MRSA in Central Europe. Through the multitude of applied methods, the data from this study contribute to a more precise knowledge about the heterogeneity of MRSA in a clinical setting. Rapid dissemination of MRSA clones at a university hospital was demonstrated, indicating that dissemination may depend on the environmental conditions within the individual departments.

Bacterial Proteins↗

Limited selection of sodium channel blocking toxin-producing bacteria from paralytic shellfish toxin-contaminated mussels (Aulacomya ater).

Paralytic shellfish toxins (PSTs) are sodium channel blocking (SCB) toxins, produced by cyanobacteria, as well as by marine dinoflagellates and their associated bacteria, and cause serious health and economic concern worldwide. In a previous study, approximately 70% of the bacteria enriched from PST-contaminated shellfish tissue and isolated on marine agar medium were observed to produce SCB toxins. In the study reported here, the high percentage of cultivable toxigenic bacteria is demonstrated to be obtained through a marked selection on marine agar medium. The cultivable as well as the total bacterial diversity associated with PST-contaminated shellfish collected from the Magallanes region in the south of Chile has been analysed. Approximately 80% of bacterial isolates, analysed by restriction analysis of PCR amplified ribosomal DNA (i.e., ARDRA fingerprinting), were limited to only two genotypic OTUs (operational taxonomic unit). Sequence determination and analysis of the 16S rDNA from representative isolates of both OTUs established them to be closely related to species of the Psychrobacter genus of the gamma-subclass of the Proteobacteria. The total bacterial diversity in the shellfish was further analysed, using a cultivation-independent strategy of extraction of total DNA from contaminated tissue, PCR-amplification of bacterial 16S rRNA genes, cloning of the PCR products and analysis of the cloned 16S rDNA sequence types by fingerprinting and sequencing. Only 2% of the cloned sequence types corresponded to species of the Psychrobacter genus. The 16S rDNA sequence types detected clustered with species of the y-Proteobacteria subclass, the Cytophaga-Flexibacter-Bacteroides (CFB), the Fusobacteria and the Firmicutes phyla. The level of diversity observed within the libraries of cloned 16S rDNA was markedly greater than that observed among isolates obtained through marine agar enrichment cultures from the same shellfish tissue. Additionally the predominant cloned 16S rDNA sequence types detected from samples of the surrounding seawater demonstrated no correlation with those observed in the PST-contaminated mussels.

Animals↗

Emergence of methicillin-resistant Staphylococcus aureus with Panton-Valentine leukocidin genes in central Europe.

The aim of the present study was to investigate strains of methicillin-resistant Staphylococcus aureus (MRSA) for the presence of the lukS-lukF determinant of Panton-Valentine leukocidin and to further characterize strains found to contain the genes. During the past 2 years, MRSA containing the lukS-lukF genes for Panton-Valentine leukocidin, particularly those emerging outside of hospitals, have become of interest. MRSA strains sent to the national reference center in Germany were investigated for lukS-lukF by polymerase chain reaction (PCR). If the presence of lukS-lukF was demonstrated, strains were further characterized by molecular typing (determination of SmaI pattern, spa sequence, and multilocus sequence type), PCR demonstration of resistance genes, and characterization of the SCCmec element. Since the end of 2002, MRSA containing Panton-Valentine leukocidin genes have been demonstrated as the causative agent of 28 cases of infection (9 community-acquired cases, 19 sporadic nosocomial cases) in different areas of Germany. Twenty-seven of these 28 isolates exhibited a unique pattern of genomic typing: all exhibited multilocus sequence type 80, spa sequence type 44, and a SmaI macrorestriction pattern that corresponds to a community-acquired strain of MRSA from France and Switzerland. In addition to resistance to oxacillin, the strains exhibited resistance to ciprofloxacin, tetracycline (tetM), and fusidic acid, the last of which is encoded by the far-1 gene. The far-1 gene was shown to be located on the plasmid. One isolate corresponded to community MRSA (cMRSA) of multilocus sequence type 1 from the USA.

Anti-Bacterial Agents↗

Intraepithelial DNA immunisation with a plasmid encoding a codon optimised COPV E1 gene sequence, but not the wild-type gene sequence completely protects against mucosal challenge with infectious COPV in beagles.

DNA plasmids encoding the open reading frames of canine oral papillomavirus (COPV) nonstructural early genes E1, E2, or E7 protein were delivered into both oral mucosal and cutaneous epithelial sites in beagle dogs using particle-mediated immunotherapeutic delivery (PMID) technology. Control dogs were vaccinated with plasmid encoding either hepatitis B virus surface antigen (HBVs) or COPV L1. Using a prophylactic immunisation protocol, a priming dose of plasmid DNA was followed by a booster dose 6 weeks later. Four weeks after boost, all dogs were challenged with infectious COPV particles. Following viral challenge, as shown previously (M. A. Stanley et al., 2001, Vaccine 19, 2783-2792), mucosal papillomas developed in the negative-control HBVs vaccinated dogs, but all animals in the COPV L1 group were fully protected from disease development. In the early gene-vaccinated groups five of six in the E1-vaccinated dogs, two of six in E2-vaccinated dogs, and three of six in the E7-vaccinated beagles developed oral papillomas. Compared to the HBVs negative-control group the oral papillomas that did develop in the early-gene vaccinated beagles were significantly smaller, shorter in duration, and fewer in number. Taken together the disease burden was markedly reduced and this was statistically significant. In a second experiment one group of animals was vaccinated with plasmid encoding the wild-type COPV E1 gene, and a separate group was vaccinated with plasmid encoding a synthetic codon-optimised COPV E1 gene sequence. None of the codon-optimised E1-vaccinated animals developed papillomas at any challenge site. However, all animals vaccinated with wild-type E1 had papillomas. These data suggest that immunisation by PMID with papillomavirus early genes can significantly impact upon subsequent disease development and that full protection can be achieved using improved vectors encoding codon-optimised gene sequences perhaps emphasizing the importance of antigen load in the generation of protective responses to papillomavirus proteins.

Animals↗

Using mating-type gene sequences for improved phylogenetic resolution of Collectotrichum species complexes.

Colletotrichum species are defined primarily on the basis of host preference and morphology of the organism in planta and in culture. However the genus contains several species complexes that encompass such a broad range of morphological and pathological variation that the species name is of relatively little use either to the taxonomist or plant pathologist. Phylogenetic analyses, primarily based on variable regions of the ribosomal DNA (rDNA) sequences, have indicated that these species complexes comprise a variable number of identifiable monophyletic clades. However rDNA sequences often are insufficiently diverse to fully resolve such closely related lineages. A group of isolates representing three species complexes (C. graminicola, C. gloeosporioides and C. acutatum) were analyzed by using the high mobility group (HMG)-encoding sequence of the MAT1-2 mating type sequence, which has been shown in other fungi to be especially suitable for distinguishing relationships among closely related groups. Results were compared with those obtained from analysis of variable regions of the rDNA as well as from standard morphological classification methods. Results achieved through analysis of MAT1-2 sequences correlated well with those obtained by analysis of rDNA sequences but provided significantly better resolution among the various lineages. Morphological traits, including hyphopodia size, colony appearance, spore size, appresorial shape and size and host preference, frequently were unreliable as indicators of phylogenetic association. Spore shape and hyphopodia shape more often were useful for this purpose.

Colletotrichum↗

Population structure of group B streptococcus from a low-incidence region for invasive neonatal disease.

The population structure of group B streptococcus (GBS) from a low-incidence region for invasive neonatal disease (Israel) was investigated using multilocus genotype data. The strain collection consisted of isolates from maternal carriage (n=104) and invasive neonatal disease (n=50), resolving into 46 sequence types. The most prevalent sequence types were ST-1 (17.5 %), ST-19 (10.4 %), ST-17 (9.7 %), ST-22 (8.4 %) and ST-23 (6.5 %). Serotype III was the most common, accounting for 29.2 % of the isolates. None of the serotypes was significantly associated with invasive neonatal disease. burst analysis resolved the 46 sequence types into seven lineages (clonal complexes), from which only lineage ST-17, expressing serotype III only, was significantly associated with invasive neonatal disease. Lineage ST-22 expressed mainly serotype II, and was significantly associated with carriage. The distribution of the various sequence types and lineages, and the association of lineage ST-17 with invasive disease, are consistent with the results of analyses from a global GBS isolate collection. These findings could imply that the global variation in disease incidence is independent of the circulating GBS populations, and may be more affected by other risk factors for invasive GBS disease, or by different prevention strategies.

Carrier State↗

Typing by sequencing the slpA gene of Clostridium difficile strains causing multiple outbreaks in Japan.

Previous reports have documented that a surface layer protein (SlpA) varies among Clostridium difficile isolates. The typing system by sequencing the variable region of the slpA gene was applied to typing C. difficile strains belonging to one PCR ribotype, type smz, which has been identified as frequently causing outbreaks in Japan. The PCR ribotype smz strains recovered from patients at different hospitals in Japan were examined. Among 10 type smz strains tested, three subtypes, smz-1, -2 and -3, were identified that differed from each other by one nucleotide. slpA sequence typing was also applied to direct typing on DNA extracted from stool specimens. Of 22 stool specimens examined, 17 were PCR positive for slpA; eight were typed as slpA sequence type smz-1 and nine as type smz-2. C. difficile was cultured from 12 of these 17 stool specimens, and the sequence results of the recovered isolates were compared with those from the DNA extracted from the stool specimens. In all 12 of these stool specimens, the sequence results of DNA from recovered C. difficile isolates completely agreed with those of DNA extracted directly from stool specimens. The remaining five stool specimens were culture-negative for C. difficile. Sequence typing has the advantage of enabling easy comparison of typing results among multiple laboratories via the Internet without exchanging reference strains as is required in typing systems which depend on banding-pattern analyses. slpA sequence typing appears to be a reproducible and reliable typing system for C. difficile as well as being useful for the typing of C. difficile when stool specimens contain only small numbers of C. difficile or are inappropriate for culturing.

Bacterial Proteins↗

Identity and prevalence of multilocus sequence typing-defined clones of group A streptococci within a hospital setting.

Between July and October 2003, 121 clinical isolates of group A streptococci (GAS) were collected from a London hospital and characterized by multilocus sequence typing (MLST) to determine the identity and prevalence of clones circulating within this setting. A total of 39 sequence types (ST), of which 20 were represented by a single isolate, were identified. The eight most prevalent clones among the 121 GAS were ST117/emm81 (16%), ST39/emm4 (9%), ST62/emm87 (7%), ST28/emm1 (6%), ST36/emm12 (6%), ST46/emm22 (5%), ST334/emm82 (5%), and ST101/emm89 (4%). Compared to those in the MLST database (http://spyogenes.mlst.net), 12 (31%) of the 39 STs had not been previously identified, although 7 of these differed from recognized STs at only a single locus, suggesting they were closely related to previously recognized strains. Resistance to erythromycin and tetracycline was seen in 7 and 20% of isolates, respectively, with four isolates resistant to both agents. GAS strains with higher (>80) emm types accounted for 45% of GAS isolates collected during this study. Continuing GAS surveillance, using easily comparable methods, is important for detecting changes in the character of disease-causing isolates.

Anti-Bacterial Agents↗

Nucleotide sequence-based typing of bacteria and the impact of automation.

DNA-based typing methods are increasingly important for the characterisation of bacteria. They are used to monitor the epidemiology of pathogens with public health significance and also to help understand the evolution and population biology of bacteria. However, these methods require accuracy and reproducibility and are often of a high-throughput nature. Laboratory automation is therefore the key to the successful implementation of such methods. This review describes the impact of automation on DNA-based typing methods, particularly multi-locus sequence typing (MLST), and the method components that can be automated.

Automation↗

Chromosome termini of the monocot plant Othocallis siberica are maintained by telomerase, which specifically synthesises vertebrate-type telomere sequences.

Lack of Arabidopsis-type T3AG3 telomere sequences has recently been reported for the majority of investigated taxa of the monocot order Asparagales. In order to investigate this phenomenon in more detail, we conducted extensive cytogenetic and molecular analyses of the telomeres in Othocallis siberica, a member of this order. Terminal restriction fragment analysis together with Bal31 exonuclease assay showed that chromosome termini in O. siberica are formed by long stretches (more than 10 kbp) of vertebrate-type T2AG3 repeats. In addition, telomerase activity specifically synthesising (T2AG3)n sequence was detected in O. siberica protein extracts by telomerase repeat amplification protocol (TRAP). Fluorescence in situ hybridisation (FISH) revealed the presence of the vertebrate-type T2AG3 telomere sequences at all chromosome termini and at a few additional regions of O. siberica chromosomes, whereas Arabidopsis-type T3AG3 DNA and peptide nucleic acid (PNA) probes did not hybridise to chromosomes of Othocallis, except for polymorphic blocks in chromosomes 2 (interstitial) and 4 (terminal). These interstitial/terminal regions are apparently composed of large blocks of (T2AG3)n and (T3AG3)n DNA and represent a unique example of interspersion of two types of telomeric repeats within one genome. This may be a reflection of the recent evolutionary switch from Arabidopsis- to vertebrate-type telomeric repeats in this plant group.

Base Sequence↗

Evaluation of protein A gene polymorphic region DNA sequencing for typing of Staphylococcus aureus strains.

Three hundred and twenty isolates of Staphylococcus aureus were typed by DNA sequence analysis of the X region of the protein A gene (spa). spa typing was compared to both phenotypic and molecular techniques for the ability to differentiate and categorize S. aureus strains into groups that correlate with epidemiological information. Two previously characterized study populations were examined. A collection of 59 isolates (F. C. Tenover, R. Arbeit, G. Archer, J. Biddle, S. Byrne, R. Goering, G. Hancock, G. A. Hébert, B. Hill, R. Hollis, W. R. Jarvis, B. Kreiswirth, W. Eisner, J. Maslow, L. K. McDougal, J. M. Miller, M. Mulligan, and M. A. Pfaller, J. Clin. Microbiol. 32:407-415, 1994) from the Centers for Disease Control and Prevention (CDC) was used to test for the ability to discriminate outbreak from epidemiologically unrelated strains. A separate collection of 261 isolates form a multicenter study (R. B. Roberts, A. de Lencastre, W. Eisner, E. P. Severina, B. Shopsin, B. N. Kreiswirth, and A. Tomasz, J. Infect. Dis. 178:164-171, 1998) of methicillin-resistant S. aureus in New York City (NYC) was used to compare the ability of spa typing to group strains along clonal lines to that of the combination of pulsed-field gel electrophoresis and Southern hybridization. In the 320 isolates studied, spa typing identified 24 distinct repeat types and 33 different strain types. spa typing distinguished 27 of 29 related strains and did not provide a unique fingerprint for 4 unrelated strains from the four outbreaks of the CDC collection. In the NYC collection, spa typing provided a clonal assignment for 185 of 195 strains within the five major groups previously described. spa sequencing appears to be a highly effective rapid typing tool for S. aureus that, despite some expense of specificity, has significant advantages in terms of speed, ease of use, ease of interpretation, and standardization among laboratories.

Amino Acid Sequence↗

Cloning of a rat gene encoding the histo-blood group B enzyme: rats have more than one Abo gene.

A genomic DNA fragment corresponding to exon 7 of the human ABO gene was amplified from rats of several inbred and outbred strains. Five different sequences were obtained, four of them corresponding to A-type sequences and one to a B-type sequence based on the amino acids equivalent to residues at positions 266 and 268 of the human enzymes. In rats from inbred strains, a single A-type sequence and the unique B-type sequence were found, whereas some animals of outbred strains presented two or three A-type sequences along with the B-type sequence. The complete coding sequence of the B-type gene was obtained; identification of the exon-intron boundaries, determined by comparison with rat genomic sequences from data banks, revealed that the rat B-type gene structure is identical with that of the mouse Abo gene. Compared with the human ABO gene and the rat A gene, it lacks exon 4. Like the rat A gene (symbol: Abo), the rat B gene (symbol: Abo2) is located on chromosome 3q11-q12. It could be shown by transfection experiments that the B-type cDNA encodes an active B transferase. A transcript of the B gene was found ubiquitously, whereas the B antigen was only detected in a restricted set of tissues. These data indicate that rats have at least two distinct Abo genes, one monomorphic gene encoding a B-specific enzyme and one or more genes in some cases encoding an A-specific enzyme.

ABO Blood-Group System↗

Nucleotide sequence variability in the nontranscribed spacer of the rRNA locus in the oyster parasite Perkinsus marinus.

We examined the sequence variability of the nontranscribed spacer (NTS) and internal-transcribed spacer (ITS1 and ITS2) domains of the rRNA locus of Perkinsus marinus from Maryland, Florida, and Louisiana. The sequence of P. marinus DNA including the 5S rRNA, NTS, small subunit (SSU) rRNA, ITSI, and ITS2 regions confirmed their contiguity in the rRNA locus and revealed differences at 28 positions with the SSU rRNA sequences published earlier. The 307-bp polymerase chain reaction (PCR)-amplified fragments from the NTS domain of the various P. marinus isolates revealed the presence of 2 distinct sequences, designated as types I and II, that differed at 6 defined nucleotide positions. Based on these differences, nested PCR and restriction enzyme digests were used to distinguish between the 2 types. Sequences of the ITS1 and ITS2 domains of samples from either NTS type I (n = 3) or type II (n = 3) showed no variation and were identical to published sequences. Frequencies of the P. marinus NTS sequence types I and II in infected oysters varied with the geographic origin of the samples. All Maryland samples examined (n = 19) corresponded to the NTS type I sequence, the type II was the most frequent in the Florida samples (n = 17), and both types were about equally represented in the Louisiana samples (n = 19), with both sequence types found in individual oyster specimens. Although it has been suggested that P. marinus is diploid, it remains to be determined if both NTS sequence types can be present in a single P. marinus trophozoite.

Animals↗

Sequence-based typing of exons 1-5 of a new HLA-B allele, B*3927*.

Anew human leucocyte antigen-B (HLA-B) allele, B*3927, was detected in three individuals of a Caucasian family by routine typing with sequence-specific primers (SSP). Serological typing showed B27 Bw4 and B39 Bw6, whereas SSP detected only B*27 as well as the Bw4 and Bw6 motif. The sequence of exons 1-5 of the new allele was determined by allele-specific amplification and sequencing. The new B*39 allele showed one nucleotide difference with B*390101 at position 299 in exon 2. Codon 100 changed from GAG to GTG, resulting in an amino acid substitution from glutamic acid to valine at position 76 of the mature protein. The haplotype carrying the B*3927 allele was A*010101, B*3927, Cw*120301, DRB1*0101 and DQB1*050101.

Alleles↗

International dissemination of a high virulence rabbit Staphylococcus aureus clone.

High virulence rabbit Staphylococcus aureus strains cause chronic and spreading problems of mastitis, pododermatitis and subcutaneous abscesses on rabbit flock level, whereas infections with low virulence strains are limited to individual rabbits. In the present report, 13 high virulence rabbit S. aureus strains, selected out of a large collection of strains isolated in five European countries between 1983 and 2004, were genotyped using pulsed-field gel electrophoresis, spa typing, multilocus sequence typing (MLST) and accessory gene regulator (agr) group typing. Two low virulence rabbit S. aureus strains were also included in the study. The results indicate the clonal origin of high virulence rabbit S. aureus strains present in Europe. Furthermore, the results of MLST and spa typing form a basis for international epidemiology of rabbit S. aureus strains, as these DNA sequence-based typing techniques can easily be used for intercentre comparisons.

Animals↗