Wang Dong, Fang Liang-Xing, Jiang Yu-Wei, Wu De-Shu, Jiang Qi, Sun Ruan-Yang, Wang Min-Ge, Sun Jian, Liu Ya-Hong, Liao Xiao-Ping
National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, Guangdong 510642, China.
Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong 510642, China.
J Antimicrob Chemother. 2022 Apr 27;77(5):1286-1295. doi: 10.1093/jac/dkac061.
To investigate the prevalence and molecular characteristics of fosA3 and fosA7 among Salmonella isolates.
Five hundred and fifty-one Salmonella isolates collected from food animals in China during 2016-19 were screened for fos genes. The drug resistance, serovars, clonal relationships and genetic environments of fosA were compared between fosA7- and fosA3-positive Salmonella.
A relatively high prevalence of fosA7 (9.26%) and fosA3 (6.53%) was identified. fosA3 was associated with high-level fosfomycin resistance (≥512 mg/L), while fosA7 conferred relatively low-level resistance that was independent of the presence of glucose-6-phosphate. Additionally, fosA7 could facilitate Salmonella survival under oxidative stress. Both fosA3 and fosA7 were found in diverse serovars and STs, but segregated into distinct groups. The fosA3-positive Salmonella Typhimurium/Salmonella Indiana strains showed close genetic relationships, while fosA7-positive Salmonella Meleagridis/Salmonella Agona/Salmonella Derby showed a relatively high degree of whole-genome sequence heterogeneity. fosA3 was located on conjugative IncHI2 plasmids or chromosomes, while fosA7 was strictly chromosomal. Furthermore, two strains carried large chromosomal fosA7 regions within genomic islands. The fosA3 and fosA7 contigs from our isolates and the NCBI could be segregated into four primary and distinct genomic backbones. IS26 and the antibiotic resistance genes (ARGs) blaCTX-M, blaTEM-1B and rmtB were frequently adjacent to fosA3, while fosA7-carrying contigs generally lacked mobile elements and ARGs.
fosA3 and fosA7 were the primary factors contributing to reduced fosfomycin susceptibility, to different degrees, in these Salmonella isolates. The distinct distributions and molecular characteristics of fosA7 and fosA3 indicated that their origin and evolution in Salmonella were most likely distinct.
调查沙门氏菌分离株中fosA3和fosA7的流行情况及分子特征。
对2016 - 2019年期间从中国食用动物中收集的551株沙门氏菌分离株进行fos基因筛查。比较fosA7和fosA3阳性沙门氏菌之间的耐药性、血清型、克隆关系及fosA的遗传环境。
确定fosA7（9.26%）和fosA3（6.53%）的流行率相对较高。fosA3与高水平磷霉素耐药（≥512 mg/L）相关，而fosA7赋予相对低水平耐药，且与6 - 磷酸葡萄糖的存在无关。此外，fosA7可促进沙门氏菌在氧化应激下存活。fosA3和fosA7均存在于多种血清型和序列型中，但分为不同的组。fosA3阳性的鼠伤寒沙门氏菌/印第安纳沙门氏菌菌株显示出密切的遗传关系，而fosA7阳性的火鸡沙门氏菌/阿哥纳沙门氏菌/德比沙门氏菌显示出相对较高程度的全基因组序列异质性。fosA3位于接合性IncHI2质粒或染色体上，而fosA7严格位于染色体上。此外，两株菌在基因组岛内携带大片段染色体fosA7区域。我们分离株及美国国立生物技术信息中心（NCBI）的fosA3和fosA7重叠群可分为四个主要且不同的基因组骨架。IS26及抗生素抗性基因（ARGs）blaCTX - M、blaTEM - 1B和rmtB常与fosA3相邻，而携带fosA7的重叠群通常缺乏移动元件和ARGs。
fosA3和fosA7是导致这些沙门氏菌分离株对磷霉素敏感性降低的主要因素，程度不同。fosA7和fosA3不同的分布及分子特征表明它们在沙门氏菌中的起源和进化很可能不同。
