ROD21 excision can be generated by means of two different recombination events.
Amplification of attB and attP sequences generated after type 1 and type 2 excisions were detected by nested PCR in LK5, PT4, PT1 and PT21 strains of S. Enteritidis, using primer pairs described in Table 2 and in Figure 2. PCR products for attB (A) and attP (B) sequences for each type of excision were resolved in 1% agarose gels. The sequence of each PCR product was obtained (chromatograms in each Figure) and compared with the attB and attP sequences deduced for type 1 and type 2 excisions (labeled as theoretical). attB and attP sequences are highlighted in red in both alignments and chromatograms. Expected size for each PCR product: 591 bp for type 1 excision attB, 657 bp for type 2 excision attB, 995 bp for type 1 excision attP and 1050 bp for type 2 excision attP.