Today, multi-resistant bacterial infections threaten public health. According to statistics from the UK government, over 700,000 people die from antibiotic resistance worldwide every year. The number will rise to 10 million by 2050 [1]. Pharmaceutical corporations have decreased their investments in developing novel antimicrobials for extensive research duration, exorbitant expenses, and diminished profits [2]. To deal with this serious situation, the World Health Organization (WHO) has implemented several policies to encourage the development of antimicrobials [3]. Staphylococcus aureus (S. aureus) as a widespread human pathogen responsible for community and clinical infections. S. aureus has multiple virulence factors, including toxins, enzymes, adhesins [4], and other surface proteins, which pose challenges in treating infections with antibiotics. Bacterial biofilm formation has further enhanced S. aureus resistance to traditional antibiotics, thus reducing their efficacy. It is urgent to develop new antibacterial agents with novel modes of action that can avoid the development of bacterial resistance.

Benzothiazole is a bicyclic heterocyclic compound commonly found in natural products and bioactive molecules [[4], [5], [6]]. It possesses multiple modification sites that allow for various heteroaryl substitutions of the benzothiazole moiety, leading to its diverse range of activities including antimicrobial [[7], [8], [9]], anticancer [10], anti-inflammatory [11], antimalarial [12,13] and antioxidant properties [14]. Of particular interest is its antibacterial activity, as benzothiazole derivatives have shown the ability to inhibit various targets such as DNA rotamase, MurB [15], dihydro lactamase [16], tyrosine kinase [17], dihydropteroate synthase [18], dehydrohorn squalene synthase [19], and aldose reductase [20]. Unfortunately, most of these derivatives have low susceptibility to drug-resistant bacteria.

It is necessary to develop new antimicrobials with novel mechanisms of action or structures to tackle bacterial resistance. The emergence of metal-based complexes has shown promise in the treatment of drug-resistant bacterial infection [[21], [22], [23]]. Studies have demonstrated that metal complexes based on Pt-, Ag-, Cu- and Fe- have the ability to inhibit multidrug-resistant strains [[24], [25], [26], [27], [28]]. The diverse structures of transition metal complexes and their deep action mechanisms suggest that biological activity influenced by the metals, oxidation states, and ligands [[29], [30], [31]]. Researchers have focused on ruthenium complexes as potential antibacterial agents among transition metal complexes [[32], [33], [34], [35]]. Ruthenium complexes with diverse ligands have exhibited potent antimicrobial activity against both gram-positive and gram-negative pathogenic bacteria. This is largely attributed to their ability to bind to bacterial DNA through polypyridine‑ruthenium complexes. [[36], [37], [38]].

Given the problem of bacterial resistance and based on our group's previous research on metal ruthenium complexes [[39], [40], [41]], we explored the potential of ruthenium complexes as antibacterial agents. This study described the synthesis of four ruthenium pyridine complexes by introducing the pharmacophore (2-mercaptobenzothiazole) into phenanthroline ligands. Through evaluating antimicrobial activity and investigating the antibacterial mechanism, the in vitro results indicated that compound Ru-2 displayed remarkable antibacterial activity against S. aureus while maintaining low toxicity levels. Moreover, Ru-2 exhibited strong inhibition of biofilm formation. Further examination unveiled that Ru-2 targeted the bacterial cell membrane, leading to membrane disruption and subsequent leakage of cellular contents, ultimately resulting in bacterial demise. In vivo experiments demonstrated that ruthenium metal compounds demonstrated high safety and efficacy in combating infections in mammals.