Non-Helicobacter pylori Helicobacter Species Associated with Human Disease: a Primer for the Clinical Microbiology Laboratory

Abstract

Non-Helicobacter pylori Helicobacter species represent a broad list of 34 organisms, with only 14 convincingly associated with human infections. Additionally, a significant number of these species were discovered only in the last 10 years. Major limitations in our knowledge of these organisms and their clinical relevance adds to the difficulty of culturing and characterizing the species consistently in the clinical laboratory. Further complicating the clinical correlations of these species is the inconsistency in nomenclature exhibited in published studies, which serves as a barrier to creating a universal knowledge base in clinical microbiology laboratories. This article focuses on gastric and enterohepatic Helicobacter species, with particular attention devoted to Helicobacter heilmannii and Helicobacter cinaedi. Additional information is discussed for other, less common species for which clinical associations have been consistently reported.

Introduction

Helicobacter pylori is one of the most prevalent human pathogens in the world, infecting an estimated 50% of the population (1). Thanks to the pioneering efforts of H. pylori researchers over the 30 years since its initial discovery in 1983, our knowledge of this enigmatic, fastidious pathogen has grown significantly. The cumulative work of thousands of scientists has not only defined H. pylori as a human pathogen, but further, has described its role in cancers associated with the stomach (1). In fact, in recent decades, few human pathogens have been afforded the degree of clinical and scientific investigation that H. pylori has experienced, as evidenced by the more than 36,000 publications indexed in PubMed since 1984.

The genus Helicobacter contains several other recently discovered species that are associated with human disease despite originating from various vertebrate hosts (Table 1). These species include both gastric and enterohepatic pathogens. While they are nowhere near as extensively studied as H. pylori, recent work on these Helicobacter species, along with newer available identification methods (e.g., DNA sequencing), has broadened our appreciation for these organisms. A comprehensive list of identified Helicobacter spp. is provided in Table 2; many of these species, however, are still only sparsely described (as reflected by the years in which the species were validly described), and a discussion of the majority of them is beyond the scope of this work. This review instead will focus on those members of the genus Helicobacter that are becoming increasingly recognized as significant human pathogens.