PCR banding patterns of babAB genotypes. (A) Primer pairs used for gene detection at locus A and B. The forward primers, HypDF1 and S18F1, located in the upstream region of babA or babB, are paired with BabAR1 or BabBR1 primers to determine whether the gene at locus A and B is babA or babB. (B) PCR banding patterns of genotype A B, AB B, A AB and AB AB. The AB B genotype showed two bacterial populations in the single-colony isolate, the dominant as babA and the minor as babB, at locus A. The strain with A AB genotype represented a dominant population of babB and a minor population of babA at locus B. The combination of AB B and A AB was defined as an AB AB genotype. Lane M1, a 100 bp molecular marker; lane M2, l HindIII marker. The size of PCR products at locus A and B was 2.1-2.6 kb and 1.0-1.5 kb, respectively.