目的：
含有抗微生物抗性基因（ARGs）的细菌已从包括古代微生物组在内的各种位置分离出来，表明这些基因早于抗生素的发现。为了获得有关抗生素前期ARGs的更多信息，我们检查了来自东南极洲Dome Fuji Station的冰样。

方法：
在无菌条件下从冷冻或冰芯样品（分别为n = 3; 1,200-1,400 ybp，1,700-2,100 ybp和2,200-2,800 ybp）中提取DNA，并利用全基因组扩增和PCR分析来检测ARG。

结果：
我们在1,200-1,400岁的南极冰芯（DF-63.5）中检测到含有II型二氢蝶酸合酶基因sul2和氨基糖苷磷酸转移酶基因strA和strB的2,764个碱基对基因簇。 sul2-strA-strB基因簇通常与RSF1010质粒和Tn5393转座子相关;但是，我们没有在DF-63.5样品中检测到这些元素。该基因簇显示出与现今细菌中具有的高水平的序列同一性，而strA中存在序列多态性。此外，该基因簇在大肠杆菌中的表达导致对二氢链霉素和磺胺甲恶唑的敏感性降低。

结论：
这项研究的结果进一步证明某些ARGs存在于抗生素前期。因为sul2基因赋予对合成化合物磺胺甲恶唑的抗性，我们的研究结果表明，在抗生素前期，针对合成抗菌药物的ARG出现在细菌中。

OBJECTIVES:
Bacteria harboring antimicrobial-resistance genes (ARGs) have been isolated from various locations including ancient microbiomes, indicating that these genes predate the discovery of antibiotics. To gain further information regarding ARGs in the pre-antibiotic era, we examined ice samples derived from Dome Fuji Station, Eastern Antarctica.

METHODS:
DNA was extracted from firn or ice core samples (n=3; 1,200-1,400 ybp, 1,700-2,100 ybp, and 2,200-2,800 ybp, respectively) under sterile conditions, and whole genome amplification and PCR analyses were utilized to detect ARGs.

RESULTS:
We detected a 2,764 base-pair gene cluster containing the type II dihydropteroate synthase gene sul2 and the aminoglycoside phosphotransferase genes strA and strB in the 1,200-1,400 year-old Antarctic ice core (DF-63.5). The sul2-strA-strB gene cluster is frequently associated with RSF1010 plasmid and Tn5393 transposon; however, we did not detect these elements in the DF-63.5 sample. The gene cluster exhibited high levels of sequence identity to that harbored in present-day bacteria while there were sequence polymorphisms in strA. Furthermore, expression of this gene cluster in Escherichia coli resulted in reduced susceptibility to dihydrostreptomycin and sulfamethoxazole.

CONCLUSIONS:
The results of this study provide further evidence that certain ARGs existed in the pre-antibiotic era. Because the sul2 gene confers resistance to the synthetic compound sulfamethoxazole, our findings suggest that ARGs against synthetic antimicrobials emerged in bacteria during the pre-antibiotic era.

https://www.ncbi.nlm.nih.gov/pubmed/30468914