# Fosfomycin-resistant Escherichia coli: a FosA10 case in Italy

## TL;DR

An 83-year-old woman in Italy was infected with a rare fosfomycin-resistant Escherichia coli strain producing FosA10, highlighting the need for monitoring such resistant clones.

## Contribution

The study reports the first clinical case of FosA10-producing E. coli in Italy and identifies its genomic and plasmid characteristics.

## Key findings

- The E. coli isolate FO_2 showed high-level fosfomycin resistance (MIC >128 mg/L) due to FosA10 production.
- The fosA10 gene was located on a highly conjugative IncB/O/K/Z plasmid similar to globally circulating plasmids.
- The isolate belonged to the clinically relevant E. coli ST69 lineage.

## Abstract

FosA10-producing Enterobacterales have an extremely low incidence in Europe.

In March 2024, an 83-year-old woman, hospitalized in the Modena Province, developed an infection with fosfomycin-resistant Escherichia coli. The patient was treated with piperacillin/tazobactam and, after 10 days, the clinical picture was resolved. Fosfomycin MIC was evaluated with the reference agar dilution method and the production of FosA enzymes by phenotypic testing. Genomic characterization was assessed using long-read sequencing technology on the Sequel I platform.

An E. coli isolate (FO_2) was collected from both blood and urine samples and showed high-level resistance to fosfomycin (MIC > 128 mg/L). The resistance to fosfomycin was ascribed to the production of FosA-like enzymes by phenotypic testing. The genomic analysis pointed to a FosA10-producing E. coli ST69. The fosA10 gene was carried by a highly conjugative IncB/O/K/Z plasmid that showed relevant similarities with other globally circulating plasmids.

The acquisition of rare fosA-like genes in clinically relevant clones is concerning and the dissemination of FosA-producing E. coli should be continuously monitored.