Misidentifying Helicobacter cinaedi

Abstract

In their paper Vandamme et al. (1) report on the problems associated with the proper identification of helicobacters, citing as an example Helicobacter cinaedi. This species is very heterogeneous, and they propose that several groups of helicobacters formerly thought to represent separate species, such as Helicobacter westmeadii and Helicobacter sp. Mainz, should be classified as H. cinaedi. In the course of our own work on helicobacters, we recently realized another possible source for misidentification of H. cinaedi. By genetic analysis of several type strains of helicobacters, we found a discrepancy between the type strain of H. cinaedi from the Culture Collection of the University of Goteborg (CCUG) (CCUG 18818T) and the one from the American Type Culture Collection (ATCC) (ATCC 35683T). The analysis consisted of sequencing of the 16S rRNA gene (rrs) (lengths sequenced were 1,330 bp and 1,681 bp with intervening sequence [IVS]) as well as sequencing of 480 bp of the gene for the β-subunit of the RNA polymerase (rpoB). The strains analyzed and the results of sequence comparisons are listed in Table ​Table1.1. We found a discrepancy between the H. cinaedi type strains from ATCC and CCUG of 4% for the rrs sequences and 25% for the rpoB sequences. Interestingly, the ATCC type strain showed sequence identity with the H. fennelliae type strains from the National Collection of Type Cultures, the Laboratory for Microbiology at the University of Ghent (LMG), and CCUG, also containing an IVS of about 350 bp in the rrs gene (Table ​(Table11 and GenBank accession no. {type:entrez-nucleotide,attrs:{text:M88154,term_id:47524192,term_text:M88154}}M88154). TABLE 1 Comparison of rrs and rpoB sequences from H. cinaedi and H. fennelliae type strains In order to exclude our own laboratory artifacts due to a mix-up of long-term stored strains, the two type strains for H. cinaedi were ordered separately again from ATCC and CCUG and the genetic analysis was repeated. The same sequences were obtained from the new batches and from the long-term stock cultures of the H. cinaedi type strains. The sequences determined for the comparison are available under GenBank accession no. {type:entrez-nucleotide,attrs:{text:AF348752,term_id:13430396,term_text:AF348752}}AF348752 to {type:entrez-nucleotide,attrs:{text:AF348752,term_id:13430396,term_text:AF348752}}AF348752. Our results show that, besides biological problems in identifying and characterizing H. cinaedi isolates, the reference strain to which results are compared might also add to confusion. Based on our data, one could argue that the ATCC type strain of H. cinaedi is most probably a H. fennelliae isolate, but in order to clear the situation, each culture collection should trace the origin of its corresponding type strain and probably carry out additional tests. In this context, we would like to stress the fact that the quality of the strains and services provided by the major culture collections is undoubtedly of a very high standard.