Carbapenem-resistant avian pathogenic Escherichia coli (CR-APEC) and methicillin-resistant Staphylococcus aureus (MRSA) caused significant economic losses due to biofilm and drug resistance, and Lactic acid bacteria (LAB) are potentially valuable in livestock breeding, biocontrol, and mitigation of drug resistance. In this study, Lactobacillus rhamnosus KC3 (L. rhamnosus KC3) was isolated from raw milk of healthy camels in Xinjiang, China. We then evaluated the antibacterial and antibiofilm activities of L. rhamnosus KC3 postbiotics against CR-APEC and MRSA, as well as their synergistic effects with antibiotics. Additionally, the antimicrobial compounds and their biosynthetic pathways in L. rhamnosus KC3 were characterized through enzymatic assays and genomic analysis. The results showed that L. rhamnosus KC3 postbiotics exhibited broad-spectrum antibacterial activity against eight common pathogenic bacteria (MIC = 31.25 ± 0 mg/mL), including CR-APEC and MRSA. Notably, they significantly enhanced the efficacy of β-lactam antibiotics against these resistant pathogens (FIC < 0.5), indicating strong synergy. Furthermore, at a subinhibitory concentration, L. rhamnosus KC3 postbiotics suppressed biofilm formation by more than 25% (P ≤ 0.05). Enzyme treatment revealed that L. rhamnosus KC3 may exert bacteriostatic activity through the secretion of bacteriocins, and genome analysis also indicated that its genome contains a complete gene cluster and synthesis pathway for novel IIc bacteriocins. In conclusion, this study demonstrated that L. rhamnosus KC3 from camel milk had the characteristics of antibacterial, antibiofilm, and synergistic effects with antibiotics. This strain can provide resources of microorganisms and genetic information for the novel bacteriocins discovery and application.
Keywords: Lactobacillus rhamnosus; Antibacterial and antibiofilm; Antibiotics synergy; Genomic.
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