Abstract
Vanillic acid (VA) is a flavoring agent found in edible plants and fruits. Few recent studies exhibited robust antibacterial activity of VA against several pathogen microorganisms. However, little was reported about the effect of VA on carbapenem-resistant Enterobacter cloacae (CREC). The purpose of the current study was to assess in vitro antimicrobial and antibiofilm activities of VA against CREC. Here, minimum inhibitory concentrations (MIC) of VA against CREC was determined via gradient diffusion method. Furthermore, the antibacterial mode of VA against CREC was elucidated by measuring changes in intracellular adenosine triphosphate (ATP) concentration, intracellular pH (pHin), cell membrane potential and membrane integrity. In addition, antibiofilm formation of VA was measured by crystal violet assay and visualized with field emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). The results showed that MIC of VA against E. cloacae was 600 μg/mL. VA was capable of inhibiting the growth of CREC and destroying the cell membrane integrity of CREC, as confirmed by the decrease of intracellular ATP concentration, pHin and membrane potential as well as distinctive variation in cellular morphology. Moreover, crystal violet staining, FESEM and CLSM results indicated that VA displayed robust inhibitory effects on biofilm formation of CREC and inactivated biofilm-related CREC cells. These findings revealed that VA exhibits potent antibacterial activity against CREC, and thus has potential to be exploited as a natural preservative to control the CREC associated infections.
Highlights
Enterobacter cloacae (E. cloacae) is a common gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae and can be frequently detected from human and animal excrement
There were no significant differences between cells treated at Minimum Inhibitory Concentration (MIC) and of Vanillic acid (VA), but the increase of VA concentration was positively followed by the decrease of Adenosine Triphosphate (ATP) levels
Our results demonstrated the inhibitory effect of VA on cells of carbapenem-resistant E. cloacae (CREC)-16 and the minimum inhibitory concentration was 600 μg/mL
Summary
Enterobacter cloacae (E. cloacae) is a common gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae and can be frequently detected from human and animal excrement. E. cloacae has been isolated from food processing plants, rice, seafoods and meat products, which can bring out food spoilage [1,2]. E. cloacae has recently been used as a hygiene indicator in foodstuff processing, and is one of the most challenging bacterial contaminants of raw and processed meat products, and vegetables [3]. Carbapenem-resistant E. cloacae (CREC) that can produce resistance to the last-resort carbapenem antibiotics and compromise these drugs for the treatment of life-threatening infections [4], has been recently detected in seafood originating from. Southeast Asia, such as shrimp and clams [5]. This finding indicates that the risk for exposure to Antibiotics 2019, 8, 220; doi:10.3390/antibiotics8040220 www.mdpi.com/journal/antibiotics.
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