Distribution of Major Pilin Subunit Genes Among Atypical Enteropathogenic and Influence of Growth Media on Expression of the Operon.

Atypical enteropathogenic (aEPEC) strains are unable to produce the bundle-forming pilus (BFP), which is responsible for the localized adherence pattern, a characteristic of the pathogenicity of typical EPEC strains. The lack of BFP in aEPEC strains suggests that other fimbrial or non-fimbrial adhesins are involved in their adhesion to the host cells. The aim of this study was to investigate the distribution of major subunit fimbrial genes known to be important adherence factors produced by several pathotypes in a collection of 72 aEPEC strains. Our results demonstrate that a high percentage (94-100%) of aEPEC strains harbored , and fimbrial genes. Other fimbrial genes including , and were detected at lower frequencies (1-8%). Genes encoding fimbrial subunits, which are characteristic of enteroaggregative or enterotoxigenic were not found. No correlation was found between fimbrial gene profiles and adherence phenotypes. Since all aEPEC strains contained , the major pilin gene of the common pilus (ECP), a subset of + strains was analyzed for transcription of and production of ECP upon growth in three different culture conditions at 37°C. Transcription of occurred in all conditions; however, ECP production was medium dependent. In all, the data suggest that aEPEC strains are highly heterogeneous in terms of their fimbrial gene profiles. Despite lacking BFP production, other mechanisms of cell adherence exist in aEPEC strains to ensure host colonization, e.g., mediated by other prevalent pili such as ECP. Moreover, the production of ECP by aEPEC strains might be influenced by yet unknown post-transcriptional factors.