## 1 Introduction  
Pathogenic _Escherichia coli_ can cause severe outbreaks of diarrheal and extrainitesinal diseases in both humans and animals [1; 2; 3]. The global incidence of diarrheal infection due to _E. coli_ is up to 1.7 billion cases, with a mortality of 760,000 children per year; the in-hospital mortality of _E. coli_ bloodstream infections ranged from 9.6% to 11% [4]. It has been noted that some _E. coli_ strains are not killed by colisti, a last-resort antibiotic, due to the rapid development of antibiotic resistance [5]. Therefore, it is very urgent to develop novel antibacterial drugs to fight against pathogenic _E. coli_.  
Filamenting temperature-sensitive protein Z (FtsZ) is a highly conserved prokaryotic protein that is a homolog of eukaryotic tubulin with approximately 7% sequence identity and plays an important role in prokaryotic cell division [6; 7]. FtsZ protein is present in almost all bacteria and shares 40-50% sequence similarity among most bacteria but is notably absent in eukaryotes; FtsZ is also a GTP enzyme that polymerizes into single-stranded filaments in a GTP-dependent manner and further assembles into the Z-ringon the inside of the bacterial cytoplasmic membrane [8]. FtsZ is the first molecule to assemble at the division site and recruits other proteins (including FtsA, ZapA (YgfE), etc.) involved in bacterial cell division [9; 10; 11; 12; 13]. It has been demonstrated that abnormalities in FtsZ assembly and GTPase activity may inhibit Z-ring and septum formation, leading to abnormal cell division and even cell death [14]. Therefore, targeting FtsZ or inhibiting GTPase activity for antibacterial therapy is a promising avenue; FtsZ has recently become a hopeful target for the development of novel antibacterial drugs [8].  
Natural products are seen as a rich source of potential drugs to treat bacterial infections. It is estimated that approximately 60% of drugs are derived from natural products. Currently, there are a multitude of natural compounds being evaluated as bacterial FtsZ inhibitors, including polyphenols, phenylpropanoids, and terpenoids [15]. Some polyphenols such as resveratrol, curcumin, and viriditoxin could inhibit FtsZ expression and Z-ring formation in _Bacillus subtilis_, _E. coli_, _Staphylococcus aureus_, and _Enterococci_[8; 16; 17; 18; 19; 20]. Other compounds (including cinnamaldehyde, emodin, alkaloids, etc.) prevented the assembly of FtsZ profilaments, GTPase activity, and Z-ring formation in _E. coli_[8; 19; 20]. Moreover, these natural product molecules exhibited prominent antibacterial activity, and they had low toxicity to eukaryotes and even good pharmacokinetic properties [8]. It has been proven that virtual screening, a colorimetric (Alamar blue) microdilution broth assay, and computational, biochemical, and _in vivo_ cell-based assays could be used to screen active inhibitors of FtsZ from _Staphylococcus aureus_, _Salmonella Typhi_, _Mycobacterium tuberculosis_, etc. [21; 22; 23; 24]. However, rapid and effective screening methods based on FtsZ GTPase from _E. coli_ have rarely been reported.  
In this study, to construct an efficient screening assay for novel antibacterial agents against _E. coli_, the _ftsZ_ gene was amplified from _E. coli_, cloned into the pET-28a vector, and then expressed in _E. coli_ BL21 in the presence of isopropyl \(\beta\)-D-1-thiogalactopyranoside (IPTG). After purification with the Ni\({}^{2+}\)-NTA affinity column, GTPase activity of the recombinant FtsZ protein was determined, and a rapid screening model of antibacterial agents was mainly constructed _in vitro_ based on the FtsZ GTPase activity. In addition, several active alkaloid molecules were obtained by this screening model and they had potent antibacterial activity against pathogenic _E. coli_ and other bacteria.