Phylogenetic background and virulence profile of atypical enteropathogenic Escherichia coli from a case control study using multilocus sequence typing and DNA microarray

Department of Laboratory Medicine, Children's and Women's Health, Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Department of Medical Microbiology, St. Olavs University Hospital, Trondheim, Norway; Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec J2S 7C2; and Institut für Mikrobiologie und Tierseuchen, Freie Universität Berlin, P.O. Box 040225, D-10061 Berlin, Germany

^* To whom correspondence should be addressed. Email: jan.afset{at}ntnu.no.

	Abstract

Atypical enteropathogenetic Escherichia coli (EPEC) are frequently detected in children with diarrhea, but are also a common finding in healthy children. The aim of the study was to compare phylogenetic ancestry and virulence characteristics of atypical (eae positive, stx and bfpA negative) EPEC strains from Norwegian children with (n=37) and without (n=19) diarrhea, and to search for an association between phylogenetic ancestry and diarrhea. The strains were classified in phylogenetic groups by phylogenetic marker genes, and in sequence types (STs) by multilocus sequence typing. Phylogenetic ancestry was compared with virulence characteristics based on DNA microarray analysis. Serotyping and PFGE was also done. All four phylogenetic groups, 26 different sequence types and 20 different clonal groups were represented among the 56 atypical EPEC strains. The strains were separated in three clusters by overall virulence gene profile; one large cluster with A, B1 and D strains, and two clusters with group B2 strains. There was considerable heterogeneity in PFGE profiles and serotypes, and almost half the strains were O non-typable. The efa1/lifA gene, previously shown to be statistically linked with diarrhea in this strain collection (J. Clin. Microbiol. 2006;44:3703-11), was present in 8 of 26 STs. The two phylogenetic groups B1 and D were weakly associated with diarrhea (P=0.06 and P=0.09, respectively). In contrast. group B2 was isolated most frequently from healthy controls (P=0.05). In conclusion, the atypical EPEC strains were heterogeneous both phylogenetically and in virulence profile. Phylogenetic ancestry was less useful as predictor of diarrhea than specific virulence genes.