All the Nm isolates showed reduced binding to the soluble receptor with Y34A and I91A substitutions whilst Q89A affected OpaD binding most significantly confirming previous studies (Virji et al., 1999) . Introduction of a Leu or Thr residue at position 91 was generally less disruptive to Opa interactions. I91T substitution either did not affect binding (OpaB and OpaX) or reduced binding by 50-60% (OpaD and OpaA). I91L substitution had no effect on OpaD or OpaB whilst having opposite effects on OpaA (~50% reduction) and OpaX (twofold increase) binding.