Efficacy of chelerythrine against dual-species biofilms of Staphylococcus aureus and Staphylococcus lugdunensis.

Staphylococcus aureus and Staphylococcus lugdunensis are often associated with pathogenic biofilms ranging from superficial mucosal to life-threatening systemic infections. Recent studies have reported that chelerythrine (CHE) displays antimicrobial activities against a few microorganisms, but its effects on dual-species biofilms of S. aureus and S. lugdunensis have never been reported. The purpose of this study was to investigate how dual-species biofilms of S. aureus and S. lugdunensis respond when challenged with CHE. Minimum inhibitory concentration (MIC) of CHE against planktic cells in dual-species culture was 8 µg/mL. CHE also suppressed dual-species biofilm formation at minimal biofilm inhibitory concentration (MBIC90, 4 µg/mL). Further, confocal laser scanning microscope (CLSM) using five fluorescent dyes revealed the dose-dependent reduction of the levels of three key biofilm matrix components, and reduced tolerance to gatifloxacin, of biofilms exposed to CHE. Moreover, CHE efficiently eradicated preformed dual-species biofilms at minimal biofilm eradication concentration (MBEC, 256 µg/mL). Hence, CHE has the potential to address biofilm infections of clinical course and other biofilm-related diseases caused by S. aureus and S. lugdunensis.

Anti-microbial and anti-biofilm activities of combined chelerythrine-sanguinarine and mode of action against Candida albicans and Cryptococcus neoformans in vitro.

The increasing prevalence of fungal infections coupled with emerging drug resistance has stimulated an urgent need to explore new and effective antifungal agents. Sanguinarine and chelerythrine constitute alkaloids that have exhibited antifungal activities. However, the effects of a 1:1 mixture of these agents against Candida albicans and Cryptococcus neoformans have remained largely unexplored. The purpose of this study was to assess the anti-fungal and anti-biofilm efficacy of combined chelerythrine-sanguinarine against C. albicans and C. neoformans in vitro. Combined chelerythrine-sanguinarine inhibited C. albicans and C. neoformans growth with minimum inhibitory concentrations (MICs) of 2 and 16 µg/mL, respectively, and effectively inhibited adhesion and biofilm formation of these pathogens at minimum biofilm inhibitory concentrations of 1 and 8 µg/mL. Notably, the mixture significantly eradicated mature C. albicans and C. neoformans biofilms at 8 and 128 µg/mL, respectively. In particular, the mixture was found to disrupt cell membrane integrity and enhance penetration of antibiotics into fungal cells, suggesting its antifungal mode of action. Hence, combined chelerythrine-sanguinarine shows promise as a potential anti-fungal and anti-biofilm agent for the management of serious infections caused by C. albicans and C. neoformans.

Antimicrobial and antibiofilm activities of ursolic acid against carbapenem-resistant Klebsiella pneumoniae.

Previous studies demonstrated that ursolic acid (UA) present in apple pomace displays antimicrobial activity against some microorganisms, but the underlying mechanisms associated with this activity remain unexplored. Furthermore, there are no reports on the effect of UA on carbapenem-resistant Klebsiella pneumoniae (CRKP). This study examined the antimicrobial activity and mode of action of UA against CRKP was examined. Minimum inhibitory concentration (MIC) of UA against CRKP was determined by the agar dilution method. Variations in the intracellular pH (pHin), ATP concentration, and cell membrane potential were measured to assess the influence of UA on the cell membrane. Our results show that UA was effective against CRKP at an MIC of 0.8 mg ml-1. UA disrupted the cell membrane integrity of CRKP, exhibited strong inhibitory effects against biofilm formation and biofilm-related gene expression, and inactivated CRKP cells encased in biofilms. Thus, UA shows promise for use in combination with other antibiotics to treat multidrug resistant K. pneumoniae infections.

Antimicrobial and Antibiofilm Activities of Citral Against Carbapenem-Resistant Enterobacter cloacae.

Citral that is produced in the essential oils of plants is an isomeric mixture of geranial and neral. Few recent studies exhibited robust antibacterial activity of citral against several pathogens. However, little is reported about effects of citral on carbapenem-resistant Enterobacter cloacae (CREC). The purpose of this study was to assess antibacterial and antibiofilm activities of citral against CREC. Here, minimum inhibitory concentrations (MICs) of citral against CREC were determined by the agar dilution method. Antibacterial mode of citral against CREC was elucidated by evaluating changes in intracellular adenosine triphosphate (ATP) concentration, intracellular pH (pHin), membrane potential, membrane integrity, and cell morphology. In addition, CREC cell damage within biofilms was examined by confocal laser scanning microscopy (CLSM). The results showed that the MIC of citral against CREC was 1000 µg/mL. Citral inhibited CREC growth and destroyed its cell membrane integrity, as measured by the decrease of intracellular ATP, pH, and membrane potential as well as distinctive deformation in cellular morphology. CLSM images demonstrated that citral could inactivate CREC cells within biofilms. These results revealed that citral exhibits potent antibacterial and antibiofilm activity against CREC, and thus has potential to be used as natural food preservatives to control CREC-associated infection spread.

Antibacterial Mechanism of Vanillic Acid on Physiological, Morphological, and Biofilm Properties of Carbapenem-Resistant Enterobacter hormaechei.

ABSTRACT: Many studies have evaluated the antimicrobial activity of natural products against various microorganisms, but to our knowledge there have been no studies of the possible use of natural products for their antimicrobial activity against Enterobacter hormaechei. In this study, we investigated vanillic acid (VA) for its antimicrobial activities and its modes of action against carbapenem-resistant E. hormaechei (CREH). The MIC of VA against CREH was determined by the agar diffusion method. The antibacterial action of VA against CREH was elucidated by measuring variations in intracellular ATP concentration, intracellular pH, membrane potential, and cell morphology. Moreover, the efficacy of VA against biofilm formation and VA damage to CREH cells embedded in biofilms were further explored. Our results show that VA was effective against CREH with a MIC of 0.8 mg/mL. VA could rupture the cell membrane integrity of CREH, as measured by a decrease of intracellular ATP, pH, and membrane potential, along with distinctive alternations in cell morphology. In addition, VA exerted a remarkable inhibitory effect on the biofilm formation of CREH and also killed CREH cells within biofilms. These findings show that VA has a potent antibacterial and antibiofilm activity against CREH and, hence, has the potential to be used clinically as a novel candidate agent to treat CREH infections and in the food industry as a food preservative and surface disinfectant.

Antimicrobial activity of eugenol against carbapenem-resistant Klebsiella pneumoniae and its effect on biofilms.

A preliminary study found that eugenol expressed an antibacterial activity against Klebsiella pneumoniae. However, the mechanism of action of eugenol against K. pneumoniae still remains unexplored. The aim of this study was to gain further insight into the antibacterial effect of eugenol against carbapenem-resistant Klebsiella pneumoniae (CRKP) and possible mode of action. Here, minimum inhibitory concentration (MIC) of eugenol against CRKP strains was determined using the agar dilution method. Moreover, variations in intracellular ATP concentration, intracellular pH (pHin), membrane potential and membrane integrity were measured to evaluate the effect of eugenol on cell membrane. Besides, changes in cell structure and biofilm formation of CRKP as well as biofilm-associated cell damage were determined using field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and confocal laser scanning microscopy (CLSM). Finally, gene expression of biofilm-related biosynthesis was investigated. The results showed that MICs of eugenol against four tested CRKP were 0.2 mg/mL. Eugenol damaged the cell membrane of CRKP, as evidenced by decreased intracellular ATP concentration, reduced pHin and cell membrane hyperpolarization, coupled with enhanced membrane permeability. Furthermore, eugenol compromised cell structure and induced loss of intracellular components of CRKP. Additionally, eugenol inhibited biofilm formation and inactivated biofilm CRKP cells. Finally, eugenol presented strong inhibitory effects on biofilm formation and biofilm-associated gene expression, and inactivated CRKP cells growing in biofilms. These findings suggest that eugenol exhibits antimicrobial effect against CRKP strains and could be potentially used to control CRKP-related infections.

In Vitro Antibacterial Activity and Mechanism of Vanillic Acid against Carbapenem-Resistant Enterobacter cloacae.

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.