Escherichia fergusonii

Highlights

• Escherichia fergusonii causes illness in humans and animals.

• E. fergusonii is becoming resistant to available antimicrobial therapy.

• Virulence factors of E. fergusonii are invariably identical or similar to Escherichia coli.

Abstract

Escherichia fergusonii was introduced in the genus Escherichia almost 65 years later than Escherichia coli after which the genus was named. From then (1985) onwards mainly case reports on E. fergusonii associated with disease in individuals of veterinary or human origin have been reported and only very few more extensive studies became available. This has resulted in very fragmented knowledge on this organism. The aim of this manuscript is to give an overview of what is known on E. fergusonii today and to stimulate more research on this organism so that better insight can be obtained in the role that E. fergusonii plays in human and animal infections.

Introduction

Escherichia coli (Bacterium coli) has become by far the most studied bacterium in microbiological research, since its discovery by Theodor Escherich in 1885, probably due to the many different pathogenic isolates that have been recovered from various sites in humans and animals. Bacterium coli was placed in the genus Escherichia in honor of its discoverer in 1919 (Castellani and Chalmers, 1919). It has taken almost 65 years (a century after the discovery by Escherich) before the existence of other species in the genus Escherichia was reported (Farmer et al., 1985). This was probably due to the phenotypic similarity of the various species within the genus Escherichia and the fact that diagnostic tools to identify them, such as PCR (Gokhale et al., 2014, Simmons et al., 2014), whole genome sequencing (Touchon et al., 2009, Walk et al., 2009, Forgetta et al., 2012) and improved growth media including sorbitol or adonitol plates were not available until relatively recently (Pohl et al., 1984, March and Ratnam, 1986, Crawford-Miksza et al., 2009, Wragg et al., 2009, Foster et al., 2010).There are currently seven recognized species in the genus Escherichia. Besides E. coli the genus comprises the species Escherichia albertii (Huys et al., 2003), Escherichia blattae (Burgess et al., 1973), Escherichia fergusonii (Farmer et al., 1985), Escherichia hermanii (Brenner et al., 1982a) and Escherichia vulneris (Brenner et al., 1982b). Escherichia adecarboxylata has also been proposed as a species in the genus Escherichia, but was later reclassified Leclercia adecarboxylata (Tamura et al., 1986). Within the genus Escherichia, E. fergusonii is the closest relative of E. coli, as shown by DNA hybridization (64% similarity)(Lawrence et al., 1991), which may cause difficulty in the diagnostics of these species depending on the diagnostic method used. For example, the ability of E. fergusonii to acquire large portions of the E. coli genome may interfere with PCR dependent diagnostics (Fegan et al., 2006). The other members of the genus are isolated much less frequently than E. coli but from similar sites in the bodies of humans and animals. A striking feature of E. coli is the estimated number of 10,000 naturally occurring varieties/serotypes (and perhaps much more) that exist. These varieties are in part due to the huge number of subtle antigenic variations on the surface of their cells and the presence of “so called” virulence factors. The phylogeny of the genus Escherichia is a complex-story, within the family Enterobactereaceae Escherichia, Shigella and Salmonella are classified as separate genera, but it is argued by some that they are actually Escherichia species (Lan and Reeves, 2002, Escobar-Paramo et al., 2003, Hyma et al., 2005, Yang et al., 2007). Shigella spp. are clinically rather than phylogenetically defined and can be seen as pathogenetic lineages of E. coli. Salmonella was demonstrated to merit the status of a specific species (Ochman and Groisman, 1994). E. coli and Shigella genomes have 70–100% DNA homology. They are positive for indole production, lysine decarboxylase, ornithine decarboxylase and methyl red. While the four different species of Shigella are recognized as E. coli strains (vide supra), E. fergusonii (and E. albertii) are so different from this group that they merit species status (Walk et al., 2009, Forgetta et al., 2012).