The Bruce Ladder (BL) and the Bruce Ladder Suis (BLS) are two molecular typing tools designed to identify Brucella species for BL (Garci-Yoldi et al., 2006 ; Lopez-Goñi et al., 2008 ; Lopez-Goñi et al., 2011) and to differentiate Brucella suis biovars, Brucella canis and Brucella microti for the BLS (Lopez-Goňi et al. 2011 ; OIE Terrestrial Manual 2018, Chapter 3.1.4). These methods are applied on DNA extracted from calibrated suspensions of isolated strains.

Principle

Both methods consist in the separation of different DNA fragment by electrophoresis previously amplified by a multiplex Polymerase Chain Reaction.

A PCR multiplex is a method allowing the amplification of several distinct DNA fragments in one reaction, with all primers related to the amplification of different loci introduced into the same reaction tube.

Primers used for the PCRs are:

Once amplified, the DNA fragments are deposited on an agarose gel and are separated according to their size by electrophoretic migration

Interpretation

After migration, a picture is taken and the DNA fragments of samples tested are compared with the fragments of reference strains (used as controls).