Lactilactobacillus curvatus TH19-7: a broad-spectrum antimicrobial probiotic targeting skin pathogens and mitigating infection-associated dermal damage in vitro.

Effective management of skin infections requires antimicrobial agents that can eradicate pathogens and mitigate associated tissue damage. This in vitro study evaluates the potential of Lactilactobacillus curvatus TH19-7, isolated from kimchi, as a safe and broad-spectrum antimicrobial probiotic. The selected lactic acid bacterium was identified by 16S rRNA sequencing and biochemical profiling, followed by in vitro evaluation of antimicrobial activity (MIC/MBC), cellular morphology (SEM), safety (antibiotic susceptibility, hemolysis, bile salt hydrolase activity, and D-lactic acid production), antioxidant capacity (DPPH and ABTS assays), and anti-inflammatory effects assessed by macrophage viability and NO inhibition. The strain demonstrated significant bactericidal activity, with its cell-free supernatant inhibiting the growth of key cutaneous pathogens, including Staphylococcus aureus, Staphylococcus epidermis, Cutibacterium acnes, Pseudomonas aeruginosa, Escherichia coli (E. coli), and Candida albicans by 64.7-83.5% at 2.5 mg/mL. Minimum Inhibitory and Bactericidal Concentrations (MIC/MBC) confirmed high potency, with low MICs of 1.25 mg/mL against several targets. Crucially, scanning electron microscopy revealed that the antimicrobial mechanism involves direct cellular lysis and severe membrane deformation in bacterial cells, particularly with E. coli, with complete cell disruption. Beyond pathogen eradication, the strain exhibited significant radical scavenging capacity (ABTS IC₅₀ = 39.1 µg/mL) and suppressed nitric oxide production in macrophages by 34.8%, indicating potential to mitigate oxidative and inflammatory tissue damage. Furthermore, L. curvatus TH19-7 displayed a strong safety profile, demonstrating a non-hemolytic (γ-hemolytic) phenotype, susceptibility to a broad range of clinically relevant antibiotics, minimal D-lactate production, and demonstrated tolerance to simulated gastrointestinal stress conditions. These findings position L. curvatus TH19-7 as a promising topical probiotic that directly eliminates pathogens through membrane disruption and concurrently aid tissue recovery through immunomodulatory and antioxidant activities.