Proteus mirabilis (P. mirabilis), a Gram-negative, rod-shaped bacterium, is ubiquitously present in natural environments as well as within the intestinal tracts of humans and animals. We isolated P. mirabilis SH-4 from a swine sample and investigated its antibiotic resistance genes (ARGs) along with their genetic structure. In this study, we have performed antimicrobial susceptibility testing by the broth microdilution method and conducted a comprehensive analysis through whole genome sequencing (WGS) and phylogenomics of P. mirabilis strain SH-4. P. mirabilis SH-4 was found to possess a single chromosome measuring 4 123 479 base pairs in length, with a GC content of 39.06%. Besides, P. mirabilis SH-4 exhibited resistance to eleven antimicrobial agents tested. Through single nucleotide polymorphism (SNP) profiling, we revealed the genetic relationship of SH-4 with other P. mirabilis strains carrying various ARGs. WGS analysis revealed that SH-4 harbored a ΔTn7 transposon and two distinct genomic islands (GIs), designated as PmGRI-9-SH-4 and PmGRI-10-SH-4. ΔTn7 was identified, corresponding to Tn7 with an insertion of IS256 within its sequence. PmGRI-9-SH-4 displayed partial homology to PmGRI1-STP3 and PmGRI1-YN9 (China:Sichuan). Additionally, PmGRI-10-SH-4 contained composite transposons and eleven Type IV secretion system (T4SS) related genes, including traN, traU, traC, and others, with the MDR region situated near the terminus of this GI. In summary, GIs and ISs may serve as crucial facilitators in the acquisition of resistance genes in P. mirabilis. These genetic elements turn P. mirabilis into highly resistant bacteria, culminating in infections that pose significant therapeutic challenges.

Guo Pan, Xinling Zhao, Changjiang Wang, Yezhengzheng Tian, Jingyu Gao, Wanli Sha, Baishuang Yin, and Wenlong Dong. J. Microbiol. Biotechnol. 2025;35:1-11. https://doi.org/10.4014/jmb.2502.02011

This study aimed to identify a probiotic bacterium with antagonistic activity against the foodborne pathogen Staphylococcus aureus (S. aureus) and investigate the mechanism of its antibacterial components. Growth kinetics were analyzed to assess bacterial proliferation. Acid and bile salt tolerance are vital indicators for evaluating probiotic survival in the gastrointestinal tract. The results indicated that Companilactobacillus farciminis (C. farciminis) YLR-1 not only had high tolerance to salt conditions (0.03%, 0.3%, and 0.5%) but also has a high survival rate at pH 3–4. The bacteriocin-like inhibitory substance (BLIS) isolated from C. farciminis YLR-1 was dialyzed using a membrane with a molecular weight cut-off (MWCO) of 500 Da, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The results indicate that the BLIS produced by C. farciminis YLR-1 is a small-molecule peptide. BLIS displayed pH tolerance within acidic and neutral environments (4–8) and exhibited thermostability. When treated with proteinase K, the antibacterial action of BLIS was found to be inactivated. Membrane disruption mechanisms were examined using fluorescence imaging and scanning electron microscopy (SEM). SEM and fluorescence imaging revealed that BLIS-induced membrane damage in S. aureus ATCC 25923 causes cytoplasmic leakage and cell death.

The excessive use of synthetic preservatives poses significant threats to food safety and human health. This study systematically investigated the genetic characteristics of the Limosilactobacillus fermentum (L. fermentum) z-6 strain, the antibacterial properties of the bacteriocin-like substance (FC) it produces, and its mechanism of action. The results demonstrated that this bacteriocin-like substance exhibited remarkable antimicrobial activity and exceptional stability, maintaining high activity across a broad pH range (4.0–8.0) and withstanding heat treatment at 100 °C and UV irradiation, indicating robust environmental adaptability. Its proteinaceous nature was confirmed by its detection below 1 kDa on Tricine-SDS-PAGE and its inactivation by trypsin and pepsin. The FC showed broad-spectrum inhibition against foodborne pathogens, including Salmonella enterica serovar Typhimurium, E. coli, A. baumannii, S. aureus, P. mirabilis and L. monocytogenes. Mechanistic investigation demonstrated that the FC exerts antibacterial effects primarily through membrane disruption, as evidenced by a live-dead staining assay confirming significantly enhanced permeability in Salmonella enterica serovar Typhimurium, and scanning electron microscopy revealing distinct pore formation on bacterial surfaces. It is speculated that the FC produced by z-6, due to its excellent properties and outstanding antibacterial performance, could potentially serve as a natural biopreservative.

Aeromonas hydrophila is a typical pathogen that causes fish diseases and can easily infect different fish species. This study investigated the antibacterial activity, physicochemical properties and antibacterial mechanism of the BLIS UI-11 produced by Lactobacillus plantarum HYH-11, isolated from traditional kimchi in Hebei, China. It was found that BLIS UI-11 showed excellent inhibitory effect on the growth of A. hydrophila, and it also had a good antibacterial effect on various pathogens such as Vagococcus fluvialis, Listeria monocytogenes, Aeromonas dhakensis, Aeromonas salmonicida, Salmonella Typhimurium, Escherichia coli and Staphylococcus aureus. By measuring growth kinetics, it was found that the maximum antibacterial activity was reached after 30 h of culture, and both the optical density value at 600 nm (OD₆₀₀₎ and pH basically entered the stable phase after 20 h. Whole-genome analysis and gene cluster prediction identified a RiPP-like biosynthetic gene cluster, which comprises genes encoding precursor peptides, modification enzymes, and transport/immunity components. The molecular weight of the antimicrobial active substance was detected by dialysis and Tricine-SDS-PAGE, and it was shown to be an ultra-small molecular substance (<1 kDa). BLIS UI-11 was sensitive to protease K, but its antibacterial activity remained stable after treatment with acidic environment (pH 3.0–6.0), high-temperature treatment (121 °C for 30 min), and ultraviolet irradiation (4 h). After the sub-live cell assay (PI/SYTO9) and scanning electron microscopy (SEM), BLIS UI-11 inhibited the growth of bacteria by destroying the cell membrane of A. hydrophila to deform, collapse, and form holes that lead to accounting leakage. The hemolysis assay indicated that BLIS UI-11 exhibited incomplete hemolysis, suggesting its safety for application. The results showed that BLIS UI-11 produced by strain HYH-11 has great potential as an antimicrobial agent against A. hydrophila infection.

Sijia Sun, Xinling Zhao, Changjiang Wang, Guo Pan, Lirong Yang, Wanli Sha, Wenlong Dong, and Baishuang Yin. J. Microbiol. Biotechnol. 2025;35:1-10. https://doi.org/10.4014/jmb.2507.07006