Streptococcus anginosus promotes gastric inflammation, atrophy, and tumorigenesis in mice.

Streptococcus anginosus (S. anginosus) was enriched in the gastric mucosa of patients with gastric cancer (GC). Here, we show that S. anginosus colonized the mouse stomach and induced acute gastritis. S. anginosus infection spontaneously induced progressive chronic gastritis, parietal cell atrophy, mucinous metaplasia, and dysplasia in conventional mice, and the findings were confirmed in germ-free mice. In addition, S. anginosus accelerated GC progression in carcinogen-induced gastric tumorigenesis and YTN16 GC cell allografts. Consistently, S. anginosus disrupted gastric barrier function, promoted cell proliferation, and inhibited apoptosis. Mechanistically, we identified an S. anginosus surface protein, TMPC, that interacts with Annexin A2 (ANXA2) receptor on gastric epithelial cells. Interaction of TMPC with ANXA2 mediated attachment and colonization of S. anginosus and induced mitogen-activated protein kinase (MAPK) activation. ANXA2 knockout abrogated the induction of MAPK by S. anginosus. Thus, this study reveals S. anginosus as a pathogen that promotes gastric tumorigenesis via direct interactions with gastric epithelial cells in the TMPC-ANXA2-MAPK axis.

Development of a luciferase-based Gram-positive bacterial reporter system for the characterization of antimicrobial agents.

Mechanistic investigations are of paramount importance in elucidating the modes of action of antibiotics and facilitating the discovery of novel drugs. We reported a luciferase-based reporter system using bacterial cells to unveil mechanisms of antimicrobials targeting transcription and translation. The reporter gene Nluc encoding NanoLuciferase (NanoLuc) was integrated into the genome of the Gram-positive model organism, Bacillus subtilis, to generate a reporter strain BS2019. Cellular transcription and translation levels were assessed by quantifying the amount of Nluc mRNA as well as the luminescence catalyzed by the enzyme NanoLuc. We validated this system using three known inhibitors of transcription (rifampicin), translation (chloramphenicol), and cell wall synthesis (ampicillin). The B. subtilis reporter strain BS2019 successfully revealed a decline in Nluc expression by rifampicin and NanoLuc enzyme activity by chloramphenicol, while ampicillin produced no observable effect. The assay was employed to characterize a previously discovered bacterial transcription inhibitor, CUHK242, with known antimicrobial activity against drug-resistant Staphylococcus aureus. Production of Nluc mRNA in our reporter BS2019 was suppressed in the presence of CUHK242, demonstrating the usefulness of the construct, which provides a simple way to study the mechanism of potential antibiotic candidates at early stages of drug discovery. The reporter system can also be modified by adopting different promoters and reporter genes to extend its scope of contribution to other fields of work. IMPORTANCE: Discovering new classes of antibiotics is desperately needed to combat the emergence of multidrug-resistant pathogens. To facilitate the drug discovery process, a simple cell-based assay for mechanistic studies is essential to characterize antimicrobial candidates. In this work, we developed a luciferase-based reporter system to quantify the transcriptional and translational effects of potential compounds and validated our system using two currently marketed drugs. Reporter strains generated in this study provide readily available means for identifying bacterial transcription inhibitors as prospective novel antibacterials. We also provided a series of plasmids for characterizing promoters under various conditions such as stress.

Synthesis and biological evaluation of nusbiarylin derivatives as bacterial rRNA synthesis inhibitor with potent antimicrobial activity against MRSA and VRSA.

Bacterial transcription is a valid but underutilized target for antimicrobial agent discovery because of its function of bacterial RNA synthesis. Bacterial transcription factors NusB and NusE form a transcription complex with RNA polymerase for bacterial ribosomal RNA synthesis. We previously identified a series of diarylimine and -amine inhibitors capable of inhibiting the interaction between NusB and NusE and exhibiting good antimicrobial activity. To further explore the structural viability of these inhibitors, coined "nusbiarylins", 36 new derivatives containing diverse substituents at the left benzene ring of inhibitors were synthesized based upon isosteric replacement and the structure-activity relationship concluded from earlier studies. Some of the derivatives displayed good to excellent antibacterial efficacy towards a panel of clinically significant pathogens including methicillin-resistance Staphylococcus aureus (MRSA) and vancomycin-resistance S. aureus (VRSA). In particular, compound 22r exhibited the best antimicrobial activity with a minimum inhibitory concentration (MIC) of 0.5 µg/mL. Diverse mechanistic studies validated the capability of 22r inhibiting the function of NusB protein and bacterial rRNA synthesis. In silico study of drug-like properties also provided promising results. Overall, this series of derivatives showed potential antimicrobial activity and drug-likeness and provided guidance for further optimization.