Multilocus sequence typing

Genetic engineering procedure in which several different loci (usually seven) are amplified from the bacterial or mycogenic genome and their sequences are determined. The loci examined are relatively highly conserved regions of so-called "house-keeping" genes, which are involved in the central metabolism, but which nevertheless exhibit a certain degree of variability. Based on this sequence variation, different isolates of the same species can be distinguished and assigned to sequence types or so-called clonal complexes.

Only pure cultures of the pathogens in question can be used as test material. Mixed cultures can lead to unusable or falsified results. A single colony is required as a minimum.

Although MLST and MLVA are more selective than other genotyping methods, they are labor-intensive and expensive.

The sequences are generally compared with a database available on the Internet, either at http://www.mlst.net or http://pubmlst.org , depending on the species. The database contains all known sequence variants(alleles) for the individual loci studied. These are labeled with numbers, which are assigned to the sequences determined in the case of a sequence match. For each gene (allele) there is a number and thus a numerical code usually consisting of 7 positions (allele profile), depending on how many loci are to be examined for the respective organism.

Already known combinations of the 7 allele numbers are each assigned a sequence type (ST). The MLST sequence type of the organism to be examined is obtained by matching the usually seven-digit allele combination obtained.

The questions for MLST typing are primarily epidemiological in nature, but it is also possible to trace transmission routes, at least in part.

As a large number of allele variants exist for each of the loci studied, resulting in a very high number of allele profiles, the chance occurrence of an identical MLST profile in two isolates would be very unlikely and two isolates with identical allele profiles can therefore be assigned to the same clone.

If different MLST types are present, transmission from one patient to other patients examined can be ruled out, whereas an identical MLST type in two or more patients does not constitute proof of transmission, but does indicate an outbreak.