Illustration of the MLVA assay set-up The PCR products of an amplification using primers "ms01" (on the left) or primers "ms04" (on the right) have been loaded on an agarose gel, electrophoresed, and stained with ethidium bromide. Lanes M are a 20 bp ladder molecular weight marker. Samples 1 to 7 correspond to a Yersinia pseudotuberculosis strain (lane 1), Yersinia pestis strains representing genotype 18 in Figure 2 (EV76 DNA from 4 different origins, lanes 2, 4, 5, 7, and a strain from Turkey, lane 6), Yersinia pestis strain KIM (lane 3). The image illustrates how the number of units can be directly deduced by manual reading. The marker names below the gel provide the repeat unit size of the tandem repeat, the expected PCR product size in the CO92 genome, and the corresponding number of units in the CO92 genome.