mlstdbNet – distributed multi-locus sequence typing (MLST) databases
© Jolley et al; licensee BioMed Central Ltd. 2004
Received: 26 May 2004
Accepted: 01 July 2004
Published: 01 July 2004
Multi-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.
The 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.
Development 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.
Multi-Locus Sequence Typing (MLST) is a method for characterising microbial isolates by means of sequencing internal fragments of housekeeping genes . It was designed primarily for global epidemiology and surveillance  and has the advantages that data are highly reproducible and can be shared over the Internet without the need for exchanging live cultures. Fragments of approximately 500 bp length of usually between six and eight loci are sequenced, with each unique fragment sequence assigned an allele marker. Each allelic combination, or profile, is then assigned a sequence type (ST) number.
Following the introduction of MLST, database software was developed  that worked well for the small datasets initially produced. This was used to run the MLST websites that act as central repositories for sequence and profile definitions, as well as providing information on submitted isolates. It became apparent, however, that the original monolithic design had problems of scalability and data redundancy, while also requiring all isolate data to be submitted to a central database – which is often inappropriate in the public health setting. To overcome these issues, a new distributed database structure was required that enabled alleles and profiles to be defined centrally while allowing individual laboratories to host and control their own isolate databases. Here we describe mlstdbNet, a package that implements a network of web-accessible MLST databases that can be linked widely over the Internet. The central profiles database can be queried directly or via network protocols by client databases or other software.
The premise behind the design of mlstdbNet was that isolate-specific information should be separated from allelic profiles and nucleotide sequences that may be shared by multiple isolates. By storing the profile and sequence data in its own database, any number of isolate databases can be constructed, each of which can interact with this profiles database but whose structure is not constrained by it. Consequently isolate databases can be set up for individual projects or populations of bacteria, or by individual organisations, with access controls set and fields included appropriately, while maintaining the benefits of having a single definitive source for sequence type and allele definitions.
The mlstdbNet package uses parts of an early implementation of MLST database software  and runs on Linux systems using the PostgreSQL database and Apache web server. The core software is written in Perl as a single, mod_perl compatible, CGI web script and requires, at a minimum, the CGI, DBI and XML::Parser::PerlSAX (part of libxml-perl) Perl modules. The functionality of the software can be enhanced by installing other modules and third party packages, such as EMBOSS  and Bioperl , which are used for sequence alignments, generating allele files in multiple formats and interacting with the PubMed database. Editing a single configuration file can enable the functionality offered by these external programs, but they are not required for the basic operation. Databases are specified in XML files that can be generated using 'dbConfig' . The dbConfig program is written in Java (J2RE version 1.4 or later required) and offers an easy to use graphical interface to aid database design. As well as generating the database description XML file that is parsed by the web scripts, dbConfig also generates a SQL file that can be used to create the database. In addition, dbConfig will also create the configuration files for WDBI, an interface that allows the database to be curated over the web (written by Jeff Rowe, available from the mlstdbNet website ).
In addition to the script that dynamically generates the web pages, two other scripts can be run on a nightly basis. The first of these enables searching by reference by checking any database on the system for reference fields, and if it finds that a PubMed id entered in that field has not been seen before, it will download the citation from PubMed and store it in a local database. This local reference database is then used to create a searchable list of cited papers that can be selected to display information on isolates described in the paper. The other script generates an HTML page of summary statistics for the whole database.
Results and Discussion
Distributed databases using this software
Examples of public isolate databases using mlstdbNet are the 'PubMLST' databases for Neisseria , Campylobacter , Helicobacter pylori and Bacillus cereus found on the PubMLST website . These databases encourage submissions and describe the reported diversity of the organisms, but do not necessarily represent their natural populations. At least twelve other, mostly private, project- or organisation-specific isolate databases for these organisms have been established recently, all of which are clients of the central profile databases.
Apart from the distributed structure, other novel features include the graphical breakdown of datasets, including displays of allele frequency and polymorphic sites. Following a search, datasets can be exported by E-mail with a choice of included fields and sequences from isolates can be concatenated for use in external packages. An important choice available is the ability to set up an isolate database to store either ST or allelic profile information. The latter choice enables the database to be used with partial profiles so that data can be entered as soon as sequencing results are obtained, with ST and clonal complex information retrieved once the profile has been completed. Isolate information can be retrieved by exact or partial matches to any field including those stored in the profiles database. Further, the profiles database can be queried in many ways, including batch methods for profiles and sequences.
This software represents a number of important enhancements over previous systems for storing and searching MLST data. Aside from the benefits to scalability offered by the distributed structure, it enables organisations to maintain ownership and control of their own data while still benefiting from centralised assignments of allele sequences and profiles, ensuring data integrity and consistency. In many cases, data confidentiality is required for research or legislative reasons. The central profiles database can be readily mirrored to other sites as it contains no confidential data.
Availability and requirements
Project name: mlstdbNet
Project home page: http://pubmlst.org/software/database/mlstdbnet/
Operating system: Linux
Programming language: Perl
Other requirements: Apache; PostgreSQL; CGI, DBI and XML::Parser::perlSAX Perl modules
License: GNU GPL
Any restrictions to use by non-academics: none
The European Union (QLK2-CT-2001-01436) and the Wellcome Trust funded development.
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