¹School of Biological and Food Engineering, Anyang Institute of Technology, Anyang 455000, CHINA
²Haihe River Basin, Aquatic Biodiversity, Observation and Research Station of Henan Province, Anyang 456576, CHINA
³Henan Joint International Research Laboratory of Veterinary Biologics Research and Application, Anyang 455000, CHINA
⁴Zhongnongyingtai Linzhou Biological Science Park Co., Ltd., Linzhou, 456550, CHINA DOI : 10.9775/kvfd.2026.37725 This study aimed to explore the in vitro antibacterial effect of CpAtt, a novel attacin from Conogethes punctiferalis, against Streptococcus agalactiae. The minimum inhibitory concentration (MIC) was measured via broth microdilution method. Scanning electron microscopy (SEM) was applied to assess the alterations in the overall cell envelope of S. agalactiae upon CpAtt treatment. Changes in membrane permeability were characterized by detecting the leakage of intracellular nucleic acids, proteins, alkaline phosphatase (ALP), and β-galactosidase, combined with propidium iodide (PI) staining. Additionally, intracellular reactive oxygen species (ROS) levels were quantified in CpAtt-treated S. agalactiae. Additionally, intracellular reactive oxygen species (ROS) levels were detected in the CpAtt-treated S. agalactiae. The results showed that the MIC of CpAtt against S. agalactiae was 18.8 μg/mL. After 1 h of treatment with CpAtt at the concentration of 2 MIC, SEM revealed bacterial aggregation, ruptured and collapsed cell walls. CpAtt induced the massive leakage of intracellular nucleic acids and proteins in S. agalactiae. Even at low concentrations, CpAtt significantly increased extracellular activities of ALP and β-galactosidase activities, alongside elevated intracellular PI fluorescence intensity, which indicates enhanced membrane permeability of S. agalactiae. Furthermore, CpAtt significantly downregulated intracellular ROS levels. Therefore, CpAtt exerts antibacterial activity against S. agalactiae by increasing bacterial membrane permeability. These findings suggest that CpAtt is a promising candidate for developing novel antibacterial agents targeting S. agalactiae. Keywords : Streptococcus agalactiae, Attacin, Antibacterial activity, Minimum inhibitory concentration, Cell membrane permeability