Characterization and antimicrobial potential of bacteriocin-producing lactic acid bacteria isolated from the gut of <i>Blattella germanica</i>

The gut microbiota of insects plays a crucial role in host nutrition, immune regulation, and disease resistance. As a globally distributed pest, <i>Blattella germanica</i> has adapted to diverse environments and maintains a highly varied diet, making its gut microbiota a largely untapped reservoir of antimicrobial compounds. This study systematically investigated the culturable gut microbiota of <i>Blattella germanica</i>, leading to the isolation of 30 bacterial strains. Morphological characterization and 16S rRNA gene sequence analysis classified these strains into two phyla and eight genera. Among them, six lactic acid bacteria strains were found to produce bacteriocins. Notably, strain X24 exhibited the strongest antibacterial activity, particularly against <i>Escherichia coli</i>. The ethyl acetate-based extraction increased its activity by 39.50%, yielding a concentration of approximately 612.74 µg/mL. Bacteriocin X24 demonstrated a broad antimicrobial spectrum, encompassing both Gram-positive and Gram-negative bacteria as well as fungi. It showed the strongest activity against <i>Escherichia coli</i> (MIC = 37.5 µg/mL), moderate activity against <i>Staphylococcus aureus</i> and <i>Bacillus subtilis</i> (MIC = 75 µg/mL), and relatively weak activity against <i>Pseudomonas aeruginosa</i>, both standard and antibiotic-resistant <i>Salmonella typhimurium</i>, <i>Serratia marcescens</i>, and <i>Enterococcus faecalis</i> (MIC = 150 µg/mL) and <i>Saccharomyces cerevisiae</i> (MIC = 300 µg/mL). The bacteriocin demonstrated good thermostability, maintained stable antibacterial activity under neutral to slightly acidic (pH 5-7) conditions, and exhibited sensitivity to proteases. This study shows that bacteriocin-producing bacteria from German cockroach guts are a new source of bacteriocins. These could be used in food preservation, biocontrol, and reduction of antibiotic use. The work expands known bacteriocin producers and reveals insect-derived antimicrobial peptides as promising alternatives against drug-resistant pathogens.IMPORTANCEThe rise of antibiotic-resistant pathogens has intensified the search for novel antimicrobial agents. This study explores the gut microbiota of <i>Blattella germanica</i>, a highly adaptable pest, as an untapped source of bacteriocin-producing lactic acid bacteria (LAB). We identified six LAB strains with potent antimicrobial activity by producing bacteriocin, particularly X24, which exhibits broad-spectrum inhibition against Gram-positive (G⁺) and Gram-negative (G^-) pathogens, including fungi. The bacteriocin demonstrated remarkable stability under high temperatures and varying pH levels, making it a promising candidate for food preservation and biomedical applications. By uncovering the antimicrobial potential of insect-derived LAB, this research expands the diversity of bacteriocin sources and offers a sustainable strategy to combat antimicrobial resistance. Our findings highlight the ecological and biotechnological value of pest-associated microbes, paving the way for innovative alternatives to conventional antibiotics.