Study on the inhibitory effect of the fermentation product of a marine derived long branched Trichoderma ST-27 on Streptococcus agalactiae
Streptococcus agalactiae, also known as Group B Streptococcus, is a pathogenic bacterium that can cause many diseases in humans and animals. It has a colonization rate of approximately 15% to 30% in the lower digestive and urogenital tracts of healthy adults. When the human immune system is weakened or deficient, it is prone to agalactiae infection, leading to urinary tract infections, skin and soft tissue infections, and causing various adverse pregnancy outcomes such as premature birth, premature rupture of membranes, stillbirth, as well as serious neonatal infections such as neonatal sepsis and meningitis in pregnant women. In 2010, the Centers for Disease Control and Prevention (CDC) in the United States recommended penicillin as the preferred treatment for non penicillin allergic pregnant women and newborns with Streptococcus agalactiae infection. Penicillin allergic individuals use macrolide antibiotics erythromycin and/or lincomycin. Zhou et al. analyzed the clinical characteristics and drug sensitivity of newborns with different types of Streptococcus agalactiae infections. Early onset Streptococcus agalactiae infection and late onset Streptococcus agalactiae infection have different clinical characteristics. It is recommended that clinical treatment should be based on the results of Streptococcus agalactiae drug sensitivity, and antibiotics with high sensitivity rates (penicillin, vancomycin, ampicillin, and meropenem) should be selected reasonably to avoid the use of drugs with high resistance rates. Liu et al. conducted a study on the incidence of prenatal Streptococcus agalactiae infection and drug sensitivity in perinatal women, and found that the detection rate of Streptococcus agalactiae in vaginal secretions of perinatal women reached 4.74%. There was no resistance to β – lactams, but there was a decrease in penicillin sensitivity. In summary, currently the prevention and treatment of Streptococcus agalactiae mainly rely on antibiotic therapy in clinical practice. However, with the widespread use of antibiotics, the resistance of Streptococcus agalactiae has increased. For example, clindamycin and erythromycin were previously used as second-line drugs for the treatment of Streptococcus agalactiae, and now both domestic and foreign studies have reported that their resistance rates have been increasing year by year, and the domestic resistance rate has been significantly higher than that of foreign countries. Therefore, the use of biological methods and novel bioactive substances to address the increasing resistance of pathogens and their resistance has become an urgent need in the current pharmaceutical industry. Lu et al. searched for prevention and control methods for Streptococcus agalactiae in aquatic animals from the perspective of microecological prevention and control. They used 21 strains of Bacillus subtilis Baciclus as the source strain and screened a strain BA015 that had a strong inhibitory effect on Streptococcus agalactiae. They found that this strain and its fermentation broth had potential application value in the prevention and control of Streptococcus agalactiae.
Fungi of the genus Trichoderma are widely distributed around the world and have a rich variety of species. Trichoderma and its metabolites have strong inhibitory effects on various pathogenic bacteria. Compared with chemical antibiotics, they have natural, non-toxic, and pollution-free characteristics. Therefore, biological antibiotics based on Trichoderma and its metabolites have become a research hotspot. As of now, more than 140 metabolites with antibacterial effects have been isolated from Trichoderma, such as Trichoderma, Phytophthora, and Penicillin. Marine derived microorganisms have become an important resource for isolating new active metabolites, especially marine derived fungi, which have great potential to produce secondary metabolites. Most of their secondary metabolites have good biological activities, including antibacterial and anti-tumor activities. Compared to fungi isolated and identified in terrestrial environments, fungi in marine environments are rarely isolated and identified. As a complex and diverse ecosystem, the ocean has special characteristics such as high pressure, high salinity, low temperature, and oligotrophic status that are different from those of land. These factors make marine microorganisms prone to produce active substances with special functions that are different from terrestrial organisms. Therefore, the probability of finding bioactive substances with specific efficacy and novel structure from marine microorganisms is higher, which is an important resource for researching and developing new bioactive substances. Trichoderma is an important biocontrol bacterium and has been extensively studied both domestically and internationally in recent years. This article screened and obtained a strain of long branched Trichoderma ST-27 resistant to Gram positive bacteria from marine benthic animal sponges, and conducted preliminary research on the performance of its fermentation product against Streptococcus agalactiae, providing reference for the development of new biological antibacterial agents.

This article preliminarily studied the antibacterial effect of dichloromethane extract from the fermentation product of Trichoderma longum ST-27 on Streptococcus agalactiae. Through antibacterial experiments, it was found that it exhibited good inhibitory effects on three different strains of Streptococcus agalactiae. The MIC for the standard strain ATCC12386 of Streptococcus agalactiae was 0.312mg/mL, demonstrating good inhibitory activity and having certain advantages compared to commonly used antibiotics in clinical practice. The results of the effect on the growth curve of Streptococcus agalactiae showed that it has inhibitory effect on Streptococcus agalactiae at low concentrations and bactericidal effect at high concentrations. Combined with scanning electron microscopy results, it was found that the cell morphology of Streptococcus agalactiae after treatment had significant changes, and some Streptococcus agalactiae showed rupture, which proves that one of the inhibitory effects of this active substance on Streptococcus agalactiae is its biofilm. In order to further verify, transmission electron microscopy is needed to observe its ultrastructure. Streptococcus agalactiae not only exists in a planktonic state in nature, but also in the form of biofilms in many cases. Bacteria that exist in the form of biofilms are more adaptable to the external environment, have high drug resistance, and can escape the host’s immune mechanism. This study found that the dichloromethane extract of the fermentation product of Trichoderma longum ST-27 has a significant impact on the formation of biofilm on Streptococcus agalactiae. Based on this, this study provides new ideas for the prevention and treatment of Streptococcus agalactiae. At the same time, the composition of the dichloromethane extract from the fermentation product of Trichoderma longum ST-27 is not yet clear. According to relevant literature reports, the metabolites isolated from Trichoderma with antibacterial effects are mainly divided into two categories: small molecule substances, mainly including aromatic compounds, polyketones, and butenolipids; In future research, we will further analyze the components of the extracted products of large molecule substances such as Trichoderma, Mucomycin, and Antimicrobial Peptides, in order to obtain the main active substances and analyze their structures.