RESUMO
Quorum sensing (QS) is an intercellular signaling and gene regulatory mechanism that is implicated in food spoilage caused by bacteria. Thus, blocking QS may suppress QS-controlled phenotypes of these bacteria that are responsible for food spoilage. Biofilm formation is closely related to bacterial infection, and it is also a major mechanism responsible for the increased resistance of biofilm-associated bacteria to antimicrobial drugs. Food spoilage and biofilm formation caused by food-related bacteria have posed a significant problem for the food industry. Thus, adopting an antibiofilm approach would provide an alternative to an antibiotic strategy. Dihydrocoumarin is a compound that is derived from coumarin, a known natural QS inhibitor that has been used as an additive in food. Hafnia alvei is a spoilage bacterium; H. alvei H4 was isolated from ready-to-eat sea cucumber. Considering that QS and biofilm are often closely linked, this research aimed to detect the effect of dihydrocoumarin on the production of violacein by Chromobacterium violaceum 026 and to evaluate the inhibitory effect of dihydrocoumarin on the formation of biofilm by H. alvei H4 by using violacein and crystal violet assays. C. violaceum 026 treated with dihydrocoumarin showed as much as 70.1% reduction in QS-mediated production of violacein compared with untreated cells, while exhibiting no significant change in growth. H. alvei H4 treated with dihydrocoumarin displayed 75.8% reduction in swimming motility, and as much as 89.4% reduction in biofilm formation compared with the nontreated cells, with the reduction in both cases being dependent on the concentration of dihydrocoumarin. Scanning electron microscopy showed that dihydrocoumarin could effectively destroy the biofilm structure of H. alvei H4 and decrease biofilm density. These findings indicate that dihydrocoumarin can be developed into a new QS inhibitor or antibiofilm agent for controlling food spoilage and potentially investigated to increase food safety.
RESUMO
The fate of carbosulfan (seed treatment dry powder) was studied in rice field ecosystem, and a simple and reliable analytical method was developed for determination of carbosulfan, carbofuran, and 3-hydroxyl carbofuran in brown rice, rice straw, paddy water, and soil. The target compounds were extracted using acetonitrile or dichloromethane, cleaned up on acidic alumina or florisil solid phase extraction (SPE) cartridge, and analyzed by gas chromatography. The average recoveries of carbosulfan, carbofuran and 3-hydroxy carbofuran in brown rice, rice straw, paddy water, and soil ranged from 72.71% to 105.07%, with relative standard deviations of 2.00-8.80%. The limits of quantitation (LOQs) of carbosulfan, carbofuran and 3-hydroxy carbofuran in the samples (brown rice, rice straw, paddy water and soil) were 0.011, 0.0091, 0.014, 0.010 mg kg(-1), 0.016, 0.019, 0.025, 0.013 mg kg(-1), and 0.031, 0.039, 0.035, 0.036 mg kg(-1), respectively. The trials results showed that the half-lives of carbosulfan, carbofuran and 3-hydroxy carbofuran in rice straw were 4.0, 2.6 days, 3.9, 6.0 days, and 5.8, 7.0 days in Zhejiang and Hunan, respectively. Carbosulfan, carbofuran and 3-hydroxy carbofuran were detected in soils. Carbosulfan and 3-hydroxy carbofuran were almost undetectable in paddy water. Carbofuran was detected in paddy water. The final residues of carbosulfan, carbofuran and 3-hydroxy carbofuran in brown rice were lower than 0.05 mg kg(-1), which were lower than 0.5 mg kg(-1) (MRL of carbosulfan) or 0.1 mg kg(-1) (MRL of carbofuran). Therefore, a dosage of 420 g active ingredient per 100 kg seed was recommended, which could be considered as safe to human beings and animals. These would contribute to provide the scientific basis of using this insecticide.
