First enteric Escherichia fergusonii from Italy Primo isolamento enterico di Escherichia fergusonii in Italia

Escherichia fergusonii is a Gram-negative rod which belongs to the family Enterobacteriaceae. Though known to behave as a commensal organism in the gut of warm-blooded animals, knowledge regarding its natural habitat mostly remains unclear. E. fergusonii is very rarely recovered from clinical specimens and it has recently emerged as the causative agent of wound, biliary and urinary tract infections, as well as bacteraemias, enteritis and pleuritis. This organism appears closely related to Escherichia coli, and forms typical lactose non-fermenting Salmonella-like colonies on MacConkey agar [1-4]. Only one E. fergusonii strain was isolated from 2007 to date. It was collected from faeces of a hospitalized leukaemic male patient without signs of enteric infection. Strain identification was provided by bioMérieux Vitek2 and confirmed by 16S rRNA sequencing, whereas incorrect identification as Escherichia coli was obtained by the bioMérieux miniAPI. Susceptibilities were provided by Vitek2 (see Table 1) and confirmed by a CLSI disc diffusion test (discs by Liofilchem, Italy) [5]. Also, Vitek2 MIC for tigecycline was confirmed by performing an Etest (AB BIODISK), which documented an MIC of 0.19 mg/l. Lack of derepressed or inducible AmpC production, as well as ESBL (extended-spectrum betalactamase) expression, was documented by performing a disk approximation test (D-test), and an Etest ESBL screen(AB BIODISK ceftazidimeceftazidime/clavulanate and cefotaxime-cefotaxime/clavulanate commercial strips), respectively, so that the isolate was finally labelled a non-AmpC/non-ESBL phenotype [6, 7]. While ESBLs have never been found in E. fergusonii, cephalosporinases have been occasionally reported, with AmpCs being first described in 2002. Also, gentamicin is known to be poorly effective against members of this species, whilst reduced ciprofloxacin-susceptibility has been reported elsewhere. Cotrimoxazole resistance was largely described in 1999; further, lack of ampicillin and tetracycline sensitivity was reported by Farmer in 1985. Finally, piperacillin-moderately susceptible and amoxicillin/clavulanate-resistant strains first appeared in 1993, while resistance to carbapenems, tigecycline and nitrofurantoin Lettere all’Editore