Multiple Locus Variable number of tandem repeats Analysis (MLVA) is an assay based on length variation in tandem repeats of genomes. These markers (microsatellites, repeat units up to 8 bp, and minisatellites) can easily be tested for polymorphism and MLVA is one of the most widely used strategy for molecular typing of pathogenic bacteria.

 

The first MLVA Brucella assay was named "HOOF-prints" (Bricker et al., 2003). Eight highly variable loci present in most Brucella species were selected. These markers offered a very high discriminatory power (useful for outbreak investigations) but cannot provide a species assignment, especially due to a high level of homoplasy.

 

Other schemes have then been challenged and developed. The most widely used is the commonly named MLVA-16 (Le Flèche et al., 2006). This assay is divided into 2 different panels, one with a low discriminatory power (quick assignment to a species) and another one with a high discrimatory power (outbreak investigations).

 

Specific schemes related to species are regularly proposed, for example one scheme dedicated to B. suis biovar 2 named MLVA-11_suis2 (Munoz et al., 2019).

 

MLVA for Brucella is a highly powerful tool for a rapid molecular identification. Several studies are performed on a limited number of strains, but one of the main point of this method is the comparison of the results between laboratories: a public database exist and a quick comparison of the results is easy, as results are a simple numeric code. More larger studies are allowed and confirm the accuracy of MLVA-16 for Brucella typing (Vergnaud et al., 2018). Nevertheless, even MLVA is efficient for strains clustering, phylogeny can not be precisely defined, especially due to rapidly evolving markers that can suffer from hompolasy.