## 1 Introduction  
Multidrug resistant bacteria, such as _Staphylococcus aureus_ (MRSA), severely limits the effectiveness of antibiotics [1; 2]. MRSA has the highest mortality rate among multidrug resistant bacteria [3] and affects a variety of hosts, both human and animal [4]. One method of overcoming resistance is the development of new anti-infective agents that activate the host's natural immune defenses against pathogens [5; 6]. A series of strategies has been adopted to test new anti-infective agents in whole animal models such as _Caenorhabditis elegans_ (_C. elegans_) [7]. Although the common screening method for new drugs using _C. elegans_ is now widely recognized by researchers [8], the drug screening still focuses on the level of individual behavior (physiological indicators, mortality, etc.) in nematode infection models. The current understanding is that a continued increase of host-pathogen interactions and bacterial pathogenesis relies on the feedback of the innate immunity system to the external stimuli as a key link in most drug screening studies [9]. According to recent studies, the dauer formation defective-2/ dauer formation defective-16 (DAF-2/DAF-16) pathway of _C. elegans_ plays an important role in the resistance of gram negative and positive bacteria [10]. DAF-2 encodes insulin-like receptor homolog and its downstream gene _Age-1/Adap-1_ encodes phosphoinositide 3-kinase (PI3K) via the activation of serine/threonine kinases (e.g., phosphoinositide dependent protein kinase-1 (PDK-1), Protein Kinase B (AKT-1, AKT-2)) [11]. Therefore, phosphorylation of the transcription factor DAF-16 prevents its transfer from cytoplasm to the nucleus, thereby inhibiting the transcription of a series of genes [12]. If recombinant insulin-1 (INS-1) combines with DAF-2 or there is a DAF-2 function deficiency, PI3K is not activated [13]. If DAF-16 is not phosphorylated, it will enter the nucleus and regulate the expression of antibacterial genes such as _lys-7_, which is related to immunity and stress [11]. It is obvious that the DAF-2/DAF-16 pathway can be used to study the antimicrobial innate immunity of nematodes [14; 15; 16; 17]. Most reports have shown that anti-infective agents increase the survival of _Staphylococcus aureus_-infected worms by inducing the expression of the _lys-7_ gene in a DAF-16-dependent manner. These studies highlighted that the _lys-7_ antimicrobial gene expression is dependent on DAF-12/DAF-16 mediated signaling [18; 19]. Furthermore, it has been shown that c-Jun N-terminal Kinase (JNK-1), kinase germline helicase binding (KGB-1, KGB-2) and extracellular regulated protein kinases (MEK-1) participate in the activation of the innate immunity-linked Forkhead Box (FOXO)transcription factor. Thereby, DAF-16 leads to the increased production of _lys-7_ mRNA during a _Stigella flexneri_ infection [20]. Antibacterial peptides (AMPs) defend the body against exogenous pathogens. AMPs are an important part of the body's immune system and are generally composed of 10-50 amino acids [21]. It is anticipated that traditional antibiotics such as penicillin will be replaced by new antibacterial peptide drugs [22]. AMPs are expected to solve the problem of drug resistance in pathogenic bacteria [23]. Brevinin-2 is a family of peptides that has been found in the skin of certain Japanese frogs [24]. By 2018, there had been 86 peptides belonging to the Brevinin-2 family added to the Antimicrobial Peptide Database (APD) [25]. This family has 33 AMPs. Amino acid residues of homologous analysis showed that the members of the Brevinin-2 family have significant interspecific and intraspecific structural differences, with the exception of four conservative amino acid residues (Lys15, Cys27, Lys28, and Cys33) [26]. Brevinin-2 peptides derived from the pool frog and belly frog demonstrated inhibitory activity (Minimum Inhibitory Concentration (MIC) \(<\) 10 mmol/L) against the gram-negative bacterium _Escherichia coli_, the gram-positive bacteria _S. aureus_, and the fungus _Candida albicans_[27; 28].