Characterizing Antibiotic Resistance in E. coli

First, E. coli K12 (MG1655) was been sequenced (Shanghai Majorbio Bio-pharm Technology Co., Ltd), which was designated as the original wild type strain (Table 1). Activating E. coli from storage tube with glycerol stock which stored in − 80 °C, expanding propagating on a Luria Bertani (LB) agar plates, cultured at 37 °C for 16 h. The selected seed strain was cultured in LB broth at 37 °C for 12 h for following selected experiments (Li et al. 2016 (link)).Table 1

The MIC of each antibiotic to wild-type E. coli K12

No	Antibiotics	Abbreviation	Classification	Stock solution (mg/L)	MIC (mg/L)
1	ciprofloxacin	Cip	Quinolones	200	0.2
2	tetracycline	Tet	tetracyclines	10	2.34
3	Gentamicin	Gen	Aminoglycosides	10	8.75
4	polymyxin B	Pol	Polypeptides	10	0.94
5	erythromycin	Ery	Macrolides	6.4	15
6	chloramphenicol	Chl	chloramphenicols	30	4.69

The involved antibiotics: chloramphenicol (Chl), ciprofloxacin (Cip), erythromycin (Ery), gentamycin (Gen), tetracycline (Tet), and polymyxin B (Pol) and cupric (CuSO4·5H2O) were get from Solarbio, Inc. (Shanghai, China). 90% inhibition of growth was regarded as the MIC of each antibiotic, which was determined as Additional file 1: Test S1 described, and the MIC of copper ions was also investigated with the same method. The detailed accounts are displayed in Additional file 1: Text S1. The tetracycline resistant cultures were kept from light so as not to degrade the antibiotic.