Streptococcus suis is a zoonotic pathogen that is currently considered an emerging multidrug-resistant (MDR). Increasing antibiotic resistance can lead to the unsuccessful treatment of S. suis infection. Recently, many investigations of medicinal plants were conducted for the treatment of infection as a result of the increase of antibiotic-resistant bacteria. The aims of this study were to determine the chemical composition of essential oil from Syzygium aromaticum (L.) Merr. & L.M. Perry and the antibacterial activities of clove oil on MDR S. suis. Using gas chromatography coupled to a mass spectrometer, eugenol (97.76%) was found to be the major active ingredient of clove oil. In vitro antibacterial activities of clove oil against MDR S. suis were evaluated. Using the agar disc diffusion test, the clove oil showed a maximum zone of inhibition at 15% (v/v) oil concentration. In a broth microdilution method, the minimum bactericidal concentration of clove oil against all MDR S. suis isolates was 0.1% (v/v). A time-kill analysis was performed, and the killing kinetics of clove oil showed that MDR S. suis was completely reduced after 15 min of exposure to clove oil. In addition, clove oil exhibited a strong antibacterial activity at all pH values applied following incubation of MDR S. suis in pH-adjusted media with clove oil. Moreover, scanning electron microscopy revealed the nonviable S. suis isolates clearly showed atypical form and cell membrane lysis after incubation with clove oil. This study confirms the efficacy of clove oil as a natural antimicrobial against MDR S. suis and suggests the possibility of employing it as a promising alternative product for control of infectious diseases caused by S. suis in animal and human patients.

Antimicrobials are commonly used to prevent and treat disease in the ornamental fish industry. However, the indiscriminate and comprehensive overuse of unregulated antimicrobials without appropriate diagnostic examination could contribute to the development of antimicrobial-resistant strains of bacterial pathogens. Moreover, human infections caused by pathogens transmitted from fish or the aquatic environment are quite common. The frequent detection of antimicrobial resistance in ornamental fish and their environments are inevitable so as to decrease the transfer of antimicrobial-resistant bacteria from aquatic sources to other environments. This study evaluated the prevalence of common bacteria species and the antimicrobial susceptibility profile in ornamental fish that were sold in an ornamental fish shop in Chiang Mai, Thailand. Aeromonas spp. were the most dominant of the isolated species from the ornamental fish samples and accounted for 68.09% of the total. Other species detected included Vibrio spp., Pseudomonas spp., and Citrobacter spp. A high percentage of resistance to amoxicillin (93.75%), oxytetracycline (79.69%), and erythromycin (75.00%) was observed among the Aeromonas spp. The antimicrobial resistance information for ornamental fish is very limited, and the results from this study indicate that the Aeromonas spp. are highly resistant to several important antibiotics. The results suggest that additional steps should be taken to educate store owners to reduce the indiscriminate use of these antibiotics to decrease the antimicrobial resistance in ornamental fish to potentially improve public health.

Pharmaceutical products of essential oil from Zingiber cassumunar Roxb. are extensively being developed, while the research on their safety is seldom documented. The aim of the present study was to evaluate the phytochemical profile and the effect of cassumunar ginger oil on cell-based assay and the zebrafish model. The essential oil was isolated from fresh rhizomes of Z. cassumunar using simultaneous steam-distillation. Chemical composition was analyzed using gas chromatograph coupled to a mass spectrometer (GC-MS). Effect of cassumunar ginger oil on adult carp fish peripheral blood mononuclear cells (PBMCs) was investigated using MTT assay. The embryotoxic and teratogenic effects of cassumunar ginger oil were studied in zebrafish embryos. GC-MS results showed that the essential oil was composed of sabinene (43.54%) and terpinen-4-ol (29.52%) as the major phytoconstituents. No fish PBMC cytotoxic effect was observed with the concentration less than 50 µg/mL of cassumunar ginger oil. Our results showed for the first time the embryotoxic and teratogenic effects of cassumunar ginger oil in zebrafish embryos. The result indicated that the cassumunar ginger oil induced zebrafish embryotoxicity in a concentration-dependent manner. At 500 µg/mL of cassumunar ginger oil demonstrated significantly moderated embryotoxicity within 24 h (p < 0.05). The survival rate of 100 µg/mL of cassumunar ginger group was markedly declined to zero at 96-h post-fertilization (log-rank test, p = 0.001). However, survival rates of zebrafish embryo in the 1 and 10 µg/mL cassumunar ginger groups were more than 90% throughout the trial period. Moreover, very low teratogenicity to the zebrafish embryo was also observed in 1 and 10 µg/mL of cassumunar ginger groups. Our findings suggest that there is hardly any cytotoxicity, embryotoxicity and teratogenicity at concentrations less than 10 µg/mL of cassumunar ginger oil. However, the toxicity assessment of its pharmaceutical product should prove for further consumer protection.

Zingiber ottensii (ZO) Valeton, a local plant in Northern Thailand, has been widely used in traditional medicine. Many studies using in vitro models reveal its pharmacological activities, including the anti-inflammatory activity of ZO essential oil, extracted from ZO rhizomes. However, the scientific report to confirm its anti-inflammatory activity using animal models is still lacking. The present study aimed to evaluate the anti-inflammatory activity and explore the possible mechanisms of action of ZO essential oil in rats. The results revealed that ZO essential oil significantly reduced the ear edema formation induced by ethyl phenylpropiolate. Pre-treatment with ZO essential oil significantly reduced the carrageenan-induced hind paw edema and the severity of inflammation in paw tissue. In addition, pre-treatment with ZO essential oil exhibited decreased COX-2 and pro-inflammatory cytokine TNF-α expression in paw tissue, as well as PGE₂ levels in serum. On this basis, our study suggests that ZO essential oil possesses anti-inflammatory activity in animal models. Its possible mechanisms of action may involve the inhibition of TNF-α expression as well as the inhibition of COX-2 and PGE₂ production. These findings provide more crucial data of ZO essential oil that may lead to new natural anti-inflammatory product development in the future.

Zingiber ottensii Valeton (ZO) exhibits pharmacological activity and has long been used in traditional medicine. However, reports about its safety profiles are limited. The present study aimed to evaluate the phytochemical profile and the toxic effects of ZO essential oil on the development of zebrafish and acute oral toxicity in rats. The essential oil was isolated from ZO rhizomes, and phytochemicals were analyzed using a gas chromatography–mass spectrometer (GC–MS). The embryotoxic and teratogenic effects of ZO essential oil were evaluated in zebrafish embryos and larvae and the acute oral toxicity was determined in rats. GC–MS results showed the essential oil contained zerumbone as a major phytoconstituent (24.73%). The zebrafish embryotoxicity of ZO essential oil appeared to be concentration- and time-dependent manner, with a moderate LC₅₀ (1.003 µg/mL). Teratogenicity in zebrafish embryos also included morphological defects, decreased hatchability, and reduced heart rate. In rats, ZO essential oil (2000 mg/kg, p.o.) resulted in no mortality or significant toxicities. These findings suggest that ZO has embryotoxic and teratogenic effects in zebrafish embryos but does not result in death or acute oral toxicity in rats. Further long-term toxicity studies are needed to confirm the safety of products developed from ZO essential oil.