High Prevalence of Plasmid-Mediated Fosfomycin Resistance in Waterfowl-Derived Escherichia coli Strains: Insights into Genetic Context and Transmission Dynamics in China

Shaqiu Zhang ^* Jing Yang Qian Yang Qianlong Li Zhijun Zhong Mingshu Wang Renyong Jia Shun Chen Mafeng Liu Dekang Zhu Xinxin Zhao Ying Wu Qiao Yang Juan Huang Xumin Ou Di Sun Bin Tian Zhen Wu Yu He Anchun Cheng ^*

• Sichuan Agricultural University, Ya'an, China

Fosfomycin (FOS) is a critical antibiotic for treating multi-drug resistant (MDR) Enterobacteriaceae infections, but its effectiveness is jeopardized by the dissemination of plasmids encoding enzymes that modify FOS. Despite the prohibition on its use in animal breeding in China, 100 strains of Escherichia coli (E. coli) exhibiting high resistance to FOS (MIC≥512 mg/L) were isolated from samples of waterfowl origin collected in Hainan, Sichuan, and Anhui. These strains commonly carried the fosA3 (88/100, 88.0%). In addition, 21 other antimicrobial resistance genes (ARGs) were detected in these strains, with high positivity rates for tetA, aphA1, sul2, folR, qnrS and bla CTX-M . It is noteworthy that there was a significant positive correlation between the fosA3 and bla CTX-M (OR=15.162, 95% CI: 1.875-122.635). The results of pulsed-field gel electrophoresis (PFGE) demonstrated the existence of multiple dispersed clonal clusters. Multilocus sequence typing (MLST) analysis identified 45 ST types, with ST48 and ST10 representing the most dominant clones. In the conjugation experiments, 49 fosA3-positive transconjugants were obtained with a conjugation frequency as high as 1.1×10 -1 , which strongly demonstrated that the fosA3 was mainly located on the plasmid and possessed an efficient transmission ability. Whole genome sequencing (WGS) analysis further showed that the fosA3 was co-localised with the bla CTX-M on plasmids that showed a high degree of similarity in genetic structure. Of particular interest is the observation that the fosA3 is frequently accompanied by IS26 on either side of the gene. This structure may play a pivotal role in the horizontal transfer of the fosA3. The study revealed the alarming prevalence of FOS resistance in E. coli of waterfowl origin and delved deeply into the genetic characteristics and transmission mechanisms of the fosA3. Detection of plasmid-mediated, transmissible FOS resistance in waterfowl E. coli poses a threat to "One Health". Urgent need for comprehensive resistance monitoring and control strategies.