Antibacterial effect of essential oils and their components against Xanthomonas arboricola pv. pruni revealed by microdilution and direct bioautographic assays

Antibacterial activity of Cymbopogon species essential oils against Xanthomonas citri and their use in post-harvest treatment for citrus canker management

Citrus canker is a disease caused by the gram-negative bacterium Xanthomonas citri subp. citri (X. citri), which affects all commercially important varieties of citrus and can lead to significant losses. Fruit sanitization with products such as chlorine-based ones can reduce the spread of the disease. While effective, their use raises concerns about safety of the workers. This work proposes essential oils (EOs) as viable alternatives for fruit sanitization. EOs from Cymbopogon species were evaluated as to their antibacterial activity, their effect on the bacterial membrane, and their ability to sanitize citrus fruit. The in vitro assays revealed that the EOs from C. schoenanthus and C. citratus had a lower bactericidal concentration at 312 mg L-1, followed by 625 mg L-1 for C. martini and C. winterianus. Microscopy assay revealed that the bacterial cell membranes were disrupted after 15 min of contact with all EOs tested. Regarding the sanitizing potential, the EOs with higher proportions of geraniol were more effective in sanitizing acid limes. Fruit treated with C. shoenanthus and C. martini showed a reduction of ∼68% in the recovery of viable bacterial cells. Therefore, these EOs can be used as viable natural alternatives in citrus fruit disinfection.

Antibacterial effects and microarray-based molecular mechanisms of trans-cinnamaldehyde against Porphyromonas gingivalis

Porphyromonas gingivalis (P. gingivalis) is one of the keystone pathogenic bacteria of periodontitis and peri-implantitis. This study aimed to investigate the antibacterial effects and molecular mechanisms of trans-cinnamaldehyde (TC), a safe extract from natural plants, on P. gingivalis. Minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) of TC were determined, and scanning and transmission electron microscopies were used to assess the morphological changes. The overall biomass was estimated, and the metabolic activity of biofilms was determined at different TC concentrations. A microarray-based bioinformatics analysis was performed to elucidate the underlying molecular mechanisms of TC-inhibited P. gingivalis, and significant differences among groups were determined. TC showed an inhibitory effect on the proliferation and survival of planktonic P. gingivalis, of which the MIC and MBC were 39.07 μg/mL and 78.13 μg/mL, respectively. TC also significantly suppressed the formation and metabolic activity of P. gingivalis biofilm. The results of the significant pathways and gene ontology (GO) analyses revealed that TC treatment inhibited two metabolic pathways, accompanied by the downregulation of relative genes of nitrogen metabolism (NrfA, NrfH, and PG_2213) and starch and sucrose metabolism (PG_1681, PG_1682, and PG_1683). Thus, this study confirmed TC to be a natural antimicrobial agent against P. gingivalis and further demonstrated that TC suppressed the microbial activity on P. gingivalis through the disruption of physiological metabolism, which might inhibit the growth and the biofilm formation of P. gingivalis.