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 d emonstrated the presence of the gene in Hp and in two closely related gastric Helicobacters, H. nemestrinae (Hn) and H. acinonyx (Hx), but n ot in the more distantly related H. felis (Hf) and H. mustelae (Hm). T he non-gastric Helicobacters, H. canis (Hc), H. muridarum (Hr), H. fen nelliae (He) and H. cinaedi (Hi), were all negative for hpaA. An immun oblot assay of water extracts with adhesin-specific antibody confirmed these results, The deduced amino acid (aa) sequences of Hp HpaA and H n adhesin A (hereafter termed HnaA) are very similar, having identical receptor-binding motifs (rbm); also, the hemagglutination (HA) proper ties of Hn and Hp cells were indistinguishable. In contrast, the rbm o f Hx adhesin A (hereafter termed HxaA), compared to that of Hp, contai ned a non-conservative aa substitution (Ile to Thr); also, there was v ariance in five consecutive aa from 10 to 14 residues upstream from th e rbm. We conclude that these aa substitutions in HxaA are probably re sponsible for the difference in receptor recognition of this adhesin, as evidenced by the resistance of Hx HA to inhibition with N-acetylneu raminyl-alpha(2,3)-lactose. These results are consistent with the biol ogical similarity between the natural host(s) of Hp and Hn; i.e., huma n and non-human primates, and the dissimilarity between these hosts an d the feline host, the cheetah.