Housekeeping Gene Fragments Research Articles

Multilocus sequence analysis of bradyrhizobia isolated from Aeschynomene species in Senegal

This study reports the multilocus sequence analysis (MLSA) of nine house-keeping gene fragments ( atpD, dnaK, glnA, glnB, gltA, gyrB, recA, rpoB and thrC) on a collection of 38 Bradyrhizobium isolated from Aeschynomene species in Senegal, which had previously been characterised by several phenotypic and genotypic techniques, allowing a comparative analysis of MLSA resolution power for species delineation in this genus. The nifH locus was also studied to compare house-keeping and symbiotic gene phylogenies and obtain insights into the unusual symbiotic properties of these Aeschynomene symbionts. Phylogenetic analyses (maximum likelihood, Bayesian) of concatenated nine loci produced a well-resolved phylogeny of the strain collection separating photosynthetic bradyrhizobial strains (PB) from non-photosynthetic bradyrhizobial (NPB) ones. The PB clade was interpreted as the remains an expanding ancient species that presently shows high diversification, giving rise to potential new species. B. denitrificans LMG8443 and BTAi1 strains formed a sub-clade that was identified as recently emerging new species. Congruence analyses (by Shimodaira–Hasegawa (S–H) tests) identified three gene-fragments ( dnaK, glnB and recA) that should be preferred for MLSA analyses in Bradyrhizobium genus. The nine loci or nifH phylogenies were not correlated with the unusual symbiotic properties of PB (nod-dependent/nod-independent). Advantages and drawbacks of MLSA for species delineation in Bradyrhizobium are discussed.

MLST analysis reveals a highly conserved core genome among poultry isolates of Clostridium septicum

Clostridium septicum is a highly virulent, anaerobic bacterium capable of establishing necrotizing tissue infections and forming heat resistant endospores. Disease is primarily facilitated by secretion of numerous toxic products including a lethal pore-forming cytolysin. Spontaneously occurring clostridial myonecrosis involving C. septicum has recently reemerged as a concern for many poultry producers. However, despite its increasing prevalence, the epidemiology of infection and population structure of C. septicum remains largely unknown. In this study a multilocus sequence typing (MLST) approach was utilized to examine evolutionary relationships within a diverse collection of C. septicum isolates recovered from poultry flocks experiencing episodes of gangrenous dermatitis. The 109 isolates examined represented 42 turkey flocks and 24 different flocks of broiler chickens as well as C. septicum type strain, ATCC 12464. Isolates were recovered predominantly from gangrenous lesions although isolates from livers, gastrointestinal tracts, spleens and blood were included. The loci analyzed were csa, the major lethal toxin produced by C. septicum, and the housekeeping genes gyrA, groEL, dnaK, recA, tpi, ddl, colA and glpK. These loci were included in part because of their previous use in MLST analysis of Clostridium perfringens and Clostridium difficile. Results indicated a high level of conservation present within these housekeeping gene fragments when compared to what has been previously reported for the aforementioned clostridia. Of the 5352 bp of sequence data examined for each isolate, 99.7% (5335/5352) was absolutely conserved among the 109 isolates. Only one of the ten unique sequence types, or allelic profiles, identified among the isolates was recovered from both turkeys and broiler chickens suggesting some host species preference. Phylogenetic analyses identified two unique clusters, or clonal complexes, among these poultry isolates which may have important epidemiological implications for poultry producers in the United States. This work indicates a predominantly clonal population structure for C. septicum although some evidence of recombination was also observed.

SuperCAT: a supertree database for combined and integrative multilocus sequence typing analysis of the Bacillus cereus group of bacteria (including B. cereus, B. anthracis and B. thuringiensis)

The Bacillus cereus group of bacteria is an important group including mammalian and insect pathogens, such as B. anthracis, the anthrax bacterium, B. thuringiensis, used as a biological pesticide and B. cereus, often involved in food poisoning incidents. To characterize the population structure and epidemiology of these bacteria, five separate multilocus sequence typing (MLST) schemes have been developed, which makes results difficult to compare. Therefore, we have developed a database that compiles and integrates MLST data from all five schemes for the B. cereus group, accessible at http://mlstoslo.uio.no/. Supertree techniques were used to combine the phylogenetic information from analysis of all schemes and datasets, in order to produce an integrated view of the B. cereus group population. The database currently contains strain information and sequence data for 1029 isolates and 26 housekeeping gene fragments, which can be searched by keywords, MLST scheme, or sequence similarity. Supertrees can be browsed according to various criteria such as species, isolate source, or genetic distance, and subtrees containing strains of interest can be extracted. Besides analysis of the available data, the user has the possibility to enter her/his own sequences and compare them to the database and/or include them into the supertree reconstructions.

Streptococcus mutans Clonal Variation Revealed by Multilocus Sequence Typing

Streptococcus mutans is the major pathogen of dental caries, a biofilm-dependent infectious disease, and occasionally causes infective endocarditis. S. mutans strains have been classified into four serotypes (c, e, f, and k). However, little is known about the S. mutans population, including the clonal relationships among strains of S. mutans, in relation to the particular clones that cause systemic diseases. To address this issue, we have developed a multilocus sequence typing (MLST) scheme for S. mutans. Eight housekeeping gene fragments were sequenced from each of 102 S. mutans isolates collected from the four serotypes in Japan and Finland. Between 14 and 23 alleles per locus were identified, allowing us theoretically to distinguish more than 1.2 x 10(10) sequence types. We identified 92 sequence types in these 102 isolates, indicating that S. mutans contains a diverse population. Whereas serotype c strains were widely distributed in the dendrogram, serotype e, f, and k strains were differentiated into clonal complexes. Therefore, we conclude that the ancestral strain of S. mutans was serotype c. No geographic specificity was identified. However, the distribution of the collagen-binding protein gene (cnm) and direct evidence of mother-to-child transmission were clearly evident. In conclusion, the superior discriminatory capacity of this MLST scheme for S. mutans may have important practical implications.

Characterization of aBrucellasp. Strain as a Marine-Mammal Type despite Isolation from a Patient with Spinal Osteomyelitis in New Zealand

Naturally acquired infection of humans with a marine mammal-associated Brucella sp. has only been reported once previously in a study describing infections of two patients from Peru. We report the isolation and characterization of a strain of Brucella from a New Zealand patient that appears most closely related to strains previously identified from marine mammals. The isolate was preliminarily identified as Brucella suis using conventional bacteriological tests in our laboratory. However, the results profile was not an exact match, and the isolate was forwarded to four international reference laboratories for further identification. The reference laboratories identified the isolate as either B. suis or B. melitensis by traditional bacteriological methods in three laboratories and by a molecular test in the fourth laboratory. Molecular characterization by PCR, PCR-restriction fragment length polymorphism, and DNA sequencing of the bp26 gene; IS711; the omp genes omp25, omp31, omp2a, and omp2b; IRS-PCR fragments I, III, and IV; and five housekeeping gene fragments was conducted to resolve the discrepant identification of the isolate. The isolate was identified to be closely related to a Brucella sp. originating from a United States bottlenose dolphin (Tursiops truncatus) and common seals (Phoca vitulina).

First Insights into the Evolution of Streptococcus uberis : a Multilocus Sequence Typing Scheme That Enables Investigation of Its Population Biology

Intramammary infection with Streptococcus uberis is a common cause of bovine mastitis throughout the world. Several procedures to differentiate S. uberis isolates have been proposed. However, all are prone to interlaboratory variation, and none is suitable for the description of the population structure. We describe here the development of a multilocus sequence typing (MLST) scheme for S. uberis to help address these issues. The sequences of seven housekeeping gene fragments from each of 160 United Kingdom milk isolates of S. uberis were determined. Between 5 and 17 alleles were obtained per locus, giving the potential to discriminate between 1.3 x 10(7) sequence types. In this study, 57 sequence types (STs) were identified. Statistical comparisons between the maximum-likelihood trees constructed by using the seven housekeeping gene fragments showed that the congruence was no better than that between each tree and trees of random topology, indicating there had been significant recombination within these loci. The population contained one major lineage (designated the ST-5 complex). This dominated the population, containing 24 STs and representing 112 isolates. The other 33 STs were not assigned to any clonal complex. All of the isolates in the ST-5 lineage carried hasA, a gene that is essential for capsule production. There was no clear association between ST or clonal complex and disease. The S. uberis MLST system offers researchers a valuable tool that allows further investigation of the population biology of this organism and insights into the epidemiology of this disease on a global scale.

MlstdbNet – distributed multi-locus sequence typing (MLST) databases

BackgroundMulti-locus sequence typing (MLST) is a method of typing that facilitates the discrimination of microbial isolates by comparing the sequences of housekeeping gene fragments. The mlstdbNet software enables the implementation of distributed web-accessible MLST databases that can be linked widely over the Internet.ResultsThe software enables multiple isolate databases to query a single profiles database that contains allelic profile and sequence definitions. This separation enables isolate databases to be established by individual laboratories, each customised to the needs of the particular project and with appropriate access restrictions, while maintaining the benefits of a single definitive source of profile and sequence information. Databases are described by an XML file that is parsed by a Perl CGI script. The software offers a large number of ways to query the databases and to further break down and export the results generated. Additional features can be enabled by installing third-party (freely available) tools.ConclusionDevelopment of a distributed structure for MLST databases offers scalability and flexibility, allowing participating centres to maintain ownership of their own data, without introducing duplication and data integrity issues.

Collaborative consensus for optimized multilocus sequence typing of Candida albicans.

A panel of 86 different Candida albicans isolates was subjected to multilocus sequence typing (MLST) in two laboratories to obtain sequence data for 10 published housekeeping gene fragments. Analysis of data for all possible combinations of five, six, seven, eight, and nine of the fragments showed that a set comprising the fragments AAT1a, ACC1, ADP1, MPIb, SYA1, VPS13, and ZWF1b was the smallest that yielded 86 unique diploid sequence types for the 86 isolates. This set is recommended for future MLST with C. albicans.

Development of a multilocus sequence typing scheme for the pig pathogen Streptococcus suis: identification of virulent clones and potential capsular serotype exchange.

Streptococcus suis is an important pathogen of pigs and occasionally causes serious human disease. However, little is known about the S. suis population structure, the clonal relationships between strains, the potential of particular clones to cause disease, and the relevance of serotype as a marker for epidemiology. Here we describe a multilocus sequence typing (MLST) scheme for S. suis developed in order to begin to address these issues. Seven housekeeping gene fragments from each of 294 S. suis isolates obtained from various S. suis diseases and from asymptomatic carriage representing 28 serotypes and nine distinct countries of origin were sequenced. Between 32 and 46 alleles per locus were identified, giving the ability to distinguish >1.6 x 10(11) sequence types (STs). However only 92 STs were identified in this study. Of the 92 STs 18 contained multiple isolates, the most common of which, ST1, was identified on 141 occasions from six countries. Assignment of the STs to lineages resulted in 37 being identified as unique and unrelated STs while the remaining 55 were assigned to 10 complexes. ST complexes ST1, ST27, and ST87 dominate the population; while the ST1 complex was strongly associated with isolates from septicemia, meningitis, and arthritis, the ST87 and ST27 complexes were found to contain significantly higher numbers of lung isolates. In agreement with the observed distribution of disease-causing isolates of S. suis, most isolates previously characterized as of high virulence in porcine infection models belong to ST1, while isolates belonging to other STs appear to be less virulent in general. Finally nine STs were found to contain isolates of multiple serotypes, and many isolates belonging to the same serotypes were found to have very disparate genetic backgrounds. As well as highlighting that the serotype can often be a poor indicator of genetic relatedness between S. suis isolates, these findings suggest that capsular genes may be moving horizontally through the S. suis population.

Molecular typing of bacteria directly from cerebrospinal fluid.

Using Streptococcus pneumoniae as an example, the ability of multilocus sequence typing (MLST) to characterise isolates directly from cerebrospinal fluid (CSF) was investigated. A nested multiplex polymerase chain reaction method that amplifies the seven housekeeping gene fragments used for pneumococcal MLST was applied to 30 CSF samples from suspected cases of bacterial meningitis. The fragments were amplified from all 14 samples from which Streptococcus pneumoniae was cultured, and, after direct sequencing, the allelic profiles obtained from ten of the samples corresponded to those of clones previously associated with invasive pneumococcal disease. MLST could also predict the penicillin susceptibility and serotype of the CSF isolates.