Theaflavin and its derivatives exert antibacterial action against Bacillus coagulans through adsorption to cell surface phospholipids.

AIMS: To investigate the antibacterial effects of tea theaflavins and catechins against Bacillus coagulans and the underlying mechanism of antibacterial action. METHODS AND RESULTS: Bactericidal activities of theaflavin and its analogues were evaluated and compared with that of epigallocatechin gallate. Theaflavin derivatives exhibited high bactericidal activity at 50 µmol L-1 , whereas epigallocatechin gallate did not, even at 500 µmol L-1 . Furthermore, we investigated the adsorption of theaflavins to model phospholipid membranes and corresponding effects on membrane fluidity to reveal their effects on the B. coagulans cell surface. Cell membrane fluidity was decreased after treatment with theaflavin derivatives with one or more galloyl moieties. Quartz-crystal microbalance analysis showed a strong affinity of the membrane phosphatidyl glycerol (PG) bilayers for theaflavin derivatives, correlating their bactericidal activity. CONCLUSION: These findings suggest that theaflavins could effectively inhibit B. coagulans by decreasing cell membrane fluidity. SIGNIFICANCE AND IMPACT: Bacillus coagulans is a spore-forming heat-resistant bacterium responsible for spoilage in low-acidic beverages. Natural antimicrobial components in tea-based beverages are central to reducing microbial contamination and product quality deterioration, although mechanisms underlying their antimicrobial action remain obscure. This study highlights the inhibitory action of theaflavins on B. coagulans and their potential application in food and beverage industries.

Effect of epigallocatechin gallate on gene expression of Staphylococcus aureus.

OBJECTIVES: Staphylococcus aureus is an important nosocomial pathogen that produces various extracellular toxins. Epigallocatechin gallate (EGCg) is a polyphenol that is abundant in green tea. EGCg displays strong antibacterial activity against Gram-positive bacteria. The effect of EGCg on gene expression by S. aureus was investigated to clarify the mechanism underlying its antibacterial action. METHODS: Microarray analysis was performed on S. aureus treated with or without 500mg/L EGCg. Differentially expressed genes were identified and their changes at the transcription level were confirmed using real-time quantitative polymerase chain reaction (qPCR). The membrane potential of cells treated with or without EGCg were observed under fluorescence microscopy. RESULTS: Microarray analysis revealed that EGCg treatment of S. aureus resulted in increased and decreased transcription of 75 and 72 genes, respectively. Increased transcription exceeding 1-log2-fold change of genes related to membrane transport included gntP, gntK, rumA, SAOUHSC_02723, SAOUHSC_01311, and vraS. Decreased transcription was observed in genes involved in toxin production and stress response (hlgA, SAOUHSC_01110, hly, hlgB, efb, and hlgC). All changes in transcription were confirmed using real-time qPCR. The membrane potential of S. aureus treated with 500mg/L EGCg markedly decreased, indicating that EGCg damaged the cell membrane. CONCLUSIONS: S. aureus increases the transcription of genes involved in membrane transport to recover membrane function. EGCg can potentially serve as a natural antibacterial agent to control the growth and toxin production of S. aureus.

Two low-temperature-inducible Chlorella genes for delta12 and omega-3 fatty acid desaturase (FAD): isolation of delta12 and omega-3 fad cDNA clones, expression of delta12 fad in Saccharomyces cerevisiae, and expression of omega-3 fad in Nicotiana tabacum.

In an attempt to clarify the involvement of fatty acid desaturases (FADs) in the freezing tolerance of Chlorella vulgaris IAM C-27, developed by hardening, we have isolated cDNA clones for two types of FADs from the Chlorella strain, based on the sequence information of genes for delta12 and omega-3 FADs, respectively desaturating oleic acid (18:1) to linoleic acid (18:2) and linoleic acid (18:2) to linolenic acid (18:3). The deduced amino acid sequence of the first clone, designated CvFad2, showed about 66% similarity to the microsomal delta12 FADs from several higher plants and this gene had delta12 FAD activity when expressed in Saccharomyces cerevisiae. The predicted protein encoded by a second gene, designated CvFad3, showed about 60% similarity to the microsomal and plastidial omega-3 FADs from several higher plants. The features of the amino acid sequences of the C- and N-terminal regions of CvFAD3 and fatty acid analysis of polar lipids in transgenic tobacco plant expressing the CvFad3 gene suggested that this gene encodes the microsomal omega-3 FAD. Southern blot analysis showed that both genes were single-copy genes in the genome of the Chlorella strain. Different transcriptional patterns were observed with the two genes during hardening in Northern blot analysis.