## 1 Introduction  
Silver nanoparticles (AgNPs) have been established in biomedical and biological applications as one of the promising nanoparticles due to their unique physical and chemical properties, including anticancer, drug delivery, and antimicrobial agents [1, 2]. AgNPs have been reported to inhibit the growth of Gram-positive and Gram-negative pathogens [1]. The bactericidal properties of AgNPs may be attributed to the release of Ag\({}^{+}\)[3], which is toxic to microorganisms. In this regard, AgNPs have been exploited as antimicrobial agents in wound dressing, topical cream [4], and food packaging [5]. Moreover, the unrestricted use of conventional antibiotics is a critical factor in the production of resistance and the acquisition of drug resistance genes contributing to multidrug resistance [6]. Consequently, the use of AgNPs can potentially reduce the antibiotic resistance problem [7]. Over the last decade, the demand for sustainable alternatives to the conventional synthesis of AgNPs production has increased. The production of AgNPs is attained by physical and chemical methods that produce desirable size, shape, and better yield of NPs. Conventional methods, however, had significant drawbacks of high-cost production besides generating hazardous waste that causes environmental pollution. Therefore, it is imperative to look at other alternatives that are more sustainable and environmentally mild. Generally, the NPs synthesis process employing biological entities such as microorganisms has received considerable attention as an alternative to conventional methods. Microorganism-mediated NP synthesis provides an eco-friendly, simple, low-cost approach that, most importantly, does not involve any hazardous chemical. Bacteria are vastly utilized in the synthesis of NPs because they are reproducible and considered a promising nanofactory for various kinds of NPs, including gold, zinc, silver, and selenium nanoparticles [8; 9]. Certain bacteria possess unique cellular strategies for the production of NPs through the detoxification process of metal ion, mainly by metal ion biosorption and bioaccumulation [10]. Studies have confirmed that the ability of bacteria to produce NPs are highly dependent on their ability to resist the metallic ion. In particular, bacteria protect themselves from the harmful effects of metallic ion by reducing the ion into NPs with the aid of the cell membrane structure and biomolecules secreted by the cell [11; 12]. The bacterial cell membrane is composed of numerous functional groups that act as a ligand for the metallic ion [13] and site for the formation of NPs. Some studies reported the isolation of metal-tolerant microorganisms from metal-rich ecological niches to synthesize NPs. [PERSON] et al. [14] reported zinc-tolerant _Aspergillus aureus_ NJP12 isolated from the zinc mine area demonstrated interactions between its metal resistance ability and its NPs synthesis potential. Likewise, the soil fungus _Caldosporium oxysporum_ AJP03, which was isolated from a metal-rich district, exhibited gold metal tolerance and simultaneously produced gold nanoparticles [15]. Therefore, the ability of microorganisms to interact with metal ion enables them to act as the nanofactory of NPs. Several studies have been conducted on the biosynthesis of AgNPs using lactic acid bacteria (LAB), particularly probiotic bacteria. LAB are Gram-positive non-pathogenic bacteria widely found in milk and fermented food products. This bacteria also exhibit health-promoting properties [16] for human and animal consumption. Studies also indicated LAB as a promising reducing agent for AgNPs production, e.g., [PERSON] et al. [17] demonstrated that the supernatant of _Lactobacillus acidophilus_ for AgNPs synthesis produced spherical-shaped particles size ranging from 4 to 50 nm. Likewise, numerous studies reported using LAB supernatant as a reducing agent for the synthesis of AgNPs [17; 18; 19; 20].