Generation of an erythromycin-sensitive derivative of Clostridium difficile strain 630 (630Δerm) and demonstration that the conjugative transposon Tn916ΔE enters the genome of this strain at multiple sites

Erythromycin resistance in Clostridium difficile strain 630 is conferred by a genetic element termed Tn5398 which contains two erm(B) genes: erm1(B) and erm2(B). An erythromycin-sensitive derivative of strain 630 (designated 630Δerm) was generated by spontaneous mutation after continuous subculture for 30 days. This strain had lost the erm2(B) gene from within Tn5398 but retained erm1(B). However, the strain could revert to erythromycin resistance at a frequency of 2.79 × 10-8, although it still contained the deletion of erm2(B). The availability of C. difficile 630Δerm allowed the behaviour of Tn916ΔE to be investigated in this strain. This element entered the genome at multiple sites indicating that it could be useful as an insertional mutagen.