Isolation, screening, identification, and biological characterization of antagonistic strains in intestinal tract of Bombus breviceps

Abstract:

[Background] In recent years, bumblebee species and number have been decreasing worldwide due to habitat reduction, abuse of pesticides, and infection of pathogens. The pathogens can be effectively killed by the antimicrobial substances produced by microorganisms during their growth. [Objective] Bombus breviceps lives in the wild for a long time and has rich microbial resources in the intestinal tract. We screened antagonistic strains from the intestinal tract of B. breviceps and studied their antibacterial properties. [Methods] The Oxford cup double-layer method was used to screen out the antagonistic strains and determine the stability of antibacterial substances and the inhibition spectrum of the fermentation broth of the strains with strong inhibitory activity. Further, cell membrane permeability and flow cytometry were employed to investigate the inhibition mechanism. [Results] Five antagonistic strains with significant antibacterial effect were obtained, among which Fructobacillus tropaeoli CZ01 demonstrated strong inhibitory effect on all the five indicator bacteria: Staphylococcus aureus, Salmonella choleraesuis, Escherichia coli, Shigella flexneri, and Streptococcus agalactiae. It showed the strongest inhibitory effect on Staphylococcus aureus, with an inhibition zone diameter of (21.21±0.25) mm. Moreover, the inhibitory activity was still 67.36% after treatment at 121 ℃ and 78.16% after the medium was adjusted to pH 10.0. [Conclusion] B. breviceps carries rich microbial resources in intestinal tract. In particular, F. tropaeoli CZ01 with high antibacterial activity, good stability, and wide intestinal spectrum, has good killing effect on S. aureus and demonstrates good application potential.