GENETIC-EVIDENCE FOR HOST-SPECIFICITY IN THE ADHESIN-ENCODING GENES HXAA OF HELICOBACTER ACINONYX, HNAA OF H-NEMESTRINAE AND HPAA OF HELICOBACTER-PYLORI

Gastric and non-gastric species of Helicobacter were examined for the presence of the adhesin-encoding gene, hpaA, from the human-associated gastric Helicobacter H. pylori (Hp), and for adhesin subunit protein HpaA. Amplification of a 375-bp internal DNA fragment of hpaA by PCR demonstrated the presence of the gene in Hp and in two closely related gastric Helicobacters, H. nemestrinae (Hn) and H. acinonyx (Hx), but not in the more distantly related H. felis (Hf) and H. mustelae (Hm). The non-gastric Helicobacters, H. canis (Hc), H. muridarum (Hr), H. fennelliae (He) and H. cinaedi (Hi), were all negative for hpaA. An immunoblot assay of water extracts with adhesin-specific antibody confirmed these results, The deduced amino acid (aa) sequences of Hp HpaA and Hn adhesin A (hereafter termed HnaA) are very similar, having identical receptor-binding motifs (rbm); also, the hemagglutination (HA) properties of Hn and Hp cells were indistinguishable. In contrast, the rbm of Hx adhesin A (hereafter termed HxaA), compared to that of Hp, contained a non-conservative aa substitution (Ile to Thr); also, there was variance in five consecutive aa from 10 to 14 residues upstream from the rbm. We conclude that these aa substitutions in HxaA are probably responsible for the difference in receptor recognition of this adhesin, as evidenced by the resistance of Hx HA to inhibition with N-acetylneuraminyl-alpha(2,3)-lactose. These results are consistent with the biological similarity between the natural host(s) of Hp and Hn; i.e., human and non-human primates, and the dissimilarity between these hosts and the feline host, the cheetah.