Gastric Infection with Kazachstania heterogenica Influences the Outcome of a Helicobacter suis Infection in Mongolian Gerbils Bram Flahou,* Thierry De Baere, †,‡ Koen Chiers,* Frank Pasmans,* Freddy Haesebrouck* and Richard Ducatelle* *Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium, † Laboratory for Bacteriology Research (LBR), Ghent University Hospital, University of Ghent, Ghent, Belgium, ‡ Laboratory for Bacteriology, Scientific Institute of Public Health, Brussels, Belgium Helicobacter (H.) suis is a newly isolated Helicobacter species [1] colonizing the gastric mucosa of the vast majority of the pig population [2,3]. This large spiral- shaped bacterium has a role in the development of hyperkeratosis and ulcers of the pars oesophagea in the pig stomach [Meyns et al., submitted; 4]. In addition, this Helicobacter species is identical to ‘‘H. heilmannii‘‘ type 1 [4,5]. Bacteria belonging to the group comprising ‘‘H. heilmanni’’ type 1 and 2 have been associated with gastritis, gastric ulcers and even gastric MALT lymphoma in a minority of the human population [6–9]. To date, very little is known about the pathogenesis of an H. suis infection. Rodent models are commonly used to study the path- ogenesis of gastric Helicobacter infections. In H. pylori research, the mouse and the Mongolian gerbil (Meriones unguiculatus) model are the two rodent species most commonly used to investigate the interactions between this bacterium and the gastric tissue [10,11]. Also, vaccination studies against H. pylori infection are per- formed in the Mongolian gerbil model [12,13]. Besides extensive use in H. pylori research, the Mongolian gerbil has also been used to investigate the pathogenic effects of other gastric helicobacters, such as H. felis and H. bi- zzozeronii [14,15]. During a preliminary screening of a gerbil population prior to their use for the study of Keywords Mongolian gerbils, inflammation, Helicobacter suis, yeast. Reprint requests to: Bram Flahou, Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820 Merelbeke, Belgium. E-mail: bram.flahou@ ugent.be Abstract Background: The Mongolian gerbil model is often used to investigate the interactions between different gastric Helicobacter species and the gastric tissue. A preliminary screening of a gerbil population intended for use in Helicobacter suis infection studies revealed a natural yeast infection in the stomach of these animals. After identification, we have investigated the effect of the gastric yeast infection on the outcome of an experimental H. suis infection in Mongolian gerbils. Materials and methods: Yeast cells were isolated from the stomachs of Mongolian gerbils. Identification was done by Internally Transcribed rRNA Spacer 2 Region PCR fragment length analysis. To investigate a possible pathologic role of this yeast, Mongolian gerbils were infected experimentally with this yeast. Co-infection with the newly isolated H. suis was performed to investigate possible interactions between both micro-organisms. Results: Kazachstania heterogenica was found colonizing the stomach of Mongolian gerbils, mainly in the antrum. Few pathologic changes were seen in the stomachs of infected animals. Experimental co-infection of gerbils with this yeast and the newly isolated H. suis showed a significant increase in inflammation in animals infected with both micro-organisms compared to animals infected only with H. suis. Conclusions: K. heterogenica colonizes the stomach of Mongolian gerbils in exactly the same regions as gastric Helicobacter species. The uncontrolled presence of this yeast in the gerbil stomach can lead to an overestimation of the inflammation caused by Helicobacter in this animal model. Helicobacter ISSN 1523-5378 ª 2010 Blackwell Publishing Ltd, Helicobacter 15: 67–75 67