Prevalence and Characteristics of Plasmid-Mediated Fosfomycin Resistance Gene fosA3 among Salmonella Enteritidis Isolates from Retail Chickens and Children with Gastroenteritis in China

A total of 265 <i>Salmonella</i> Enteritidis isolates collected from retail markets and children's hospitals in Shanghai were used to investigate the prevalence and molecular epidemiology of plasmid-mediated fosfomycin resistance genes. Nine of the isolates-7 from the 146 (4.79%) retail chicken-related samples and 2 from the 119 (1.68%) samples from clinical children-were fosfomycin-resistant (Fos^R). The <i>fosA3</i> gene was detected in all of the nine Fos^R isolates, which were located on Inc F-type (8/9, 88.9%) and unknown-type (1/9, 11.1%) transferable plasmids. In total, five plasmid types, namely Inc HI2 (1/9, 11.1%), Inc I1 (3/9, 33.3%), Inc X (8/9, 88.9%), Inc FIIs (9/9, 100%), and Inc FIB (9/9, 100%), were detected in these Fos^R isolates, which possessed five S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) profiles. The extended-spectrum β-lactamase determinant <i>bla</i>_CTX-M-14 subtype was identified in one Fos^R<i>S.</i> Enteritidis isolate, which was located in a transferable unknown-type plasmid co-carrying <i>fosA3</i> and <i>tetR</i> genes. Sequence homology analysis showed that this plasmid possessed high sequence similarity to previously reported <i>bla</i>_CTX-M-14- and <i>fosA3</i>-positive plasmids from <i>E. coli</i> strains, implying that plasmids carrying the <i>fosA3</i> gene might be disseminated among Enterobacterales. These findings highlight further challenges in the prevention and treatment of Enterobacteriaceae infections caused by plasmids containing <i>fosA3</i>.