N-Benzylanilines as Fatty Acid Synthesis Inhibitors against Biofilm-related Methicillin-resistant Staphylococcus aureus

Insight into the Antibacterial Action of Iodinated Imine, an Analogue of Rafoxanide: a Comprehensive Study of Its Antistaphylococcal Activity

In this study, we have focused on a multiparametric microbiological analysis of the antistaphylococcal action of the iodinated imine BH77, designed as an analogue of rafoxanide. Its antibacterial activity against five reference strains and eight clinical isolates of Gram-positive cocci of the genera Staphylococcus and Enterococcus was evaluated. The most clinically significant multidrug-resistant strains, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant S. aureus (VRSA), and vancomycin-resistant Enterococcus faecium, were also included. The bactericidal and bacteriostatic actions, the dynamics leading to a loss of bacterial viability, antibiofilm activity, BH77 activity in combination with selected conventional antibiotics, the mechanism of action, in vitro cytotoxicity, and in vivo toxicity in an alternative animal model, Galleria mellonella, were analyzed. The antistaphylococcal activity (MIC) ranged from 15.625 to 62.5 μM, and the antienterococcal activity ranged from 62.5 to 125 μM. Its bactericidal action; promising antibiofilm activity; interference with nucleic acid, protein, and peptidoglycan synthesis pathways; and nontoxicity/low toxicity in vitro and in vivo in the Galleria mellonella model were found to be activity attributes of this newly synthesized compound. In conclusion, BH77 could be rightfully minimally considered at least as the structural pattern for future adjuvants for selected antibiotic drugs. IMPORTANCE Antibiotic resistance is among the largest threats to global health, with a potentially serious socioeconomic impact. One of the strategies to deal with the predicted catastrophic future scenarios associated with the rapid emergence of resistant infectious agents lies in the discovery and research of new anti-infectives. In our study, we have introduced a rafoxanide analogue, a newly synthesized and described polyhalogenated 3,5-diiodosalicylaldehyde-based imine, that effectively acts against Gram-positive cocci of the genera Staphylococcus and Enterococcus. The inclusion of an extensive and comprehensive analysis for providing a detailed description of candidate compound-microbe interactions allows the valorization of the beneficial attributes linked to anti-infective action conclusively. In addition, this study can help with making rational decisions about the possible involvement of this molecule in advanced studies or may merit the support of studies focused on related or derived chemical structures to discover more effective new anti-infective drug candidates.

Efflux pump inhibitor combined with ofloxacin decreases MRSA biofilm formation by regulating the gene expression of NorA and quorum sensing

Carbonyl cyanide p-nitrophenylhydrazone (2e) displayed a lone or synergistic efficacy against MRSA (RSC Adv., 2020, 10, 17854). In this work, the synergistic mechanism of 2e with ofloxacin was studied. MRSA2858 had potential for biofilm formation, and the value of MBEC of 2e alone was 0.78-1.56 μM, while that of 2e + ofloxacin was 0.39-0.78 μM. 2e combined with ofloxacin showed a synergistic anti-biofilm effect against MRSA. Efflux pump inhibitor 2e can better bind to NorA protein. After MRSA2858 was treated with 2e of 1/2MIC (0.78 μM) and ofloxacin of 1/8MIC (0.097 μM), the transcript levels of efflux genes (norA) and quorum-sensing (QS) regulatory genes (agrA, sarA, icaA, hla) were substantially down-regulated, and alpha-hemolysin (Hla) was inhibited by 99.15%. 2e combined with ofloxacin was more effective than 2e alone in reducing bacterial load in vivo. All in all, efflux pump inhibitor 2e enhanced the bactericidal activities of antibiotics through regulating the gene expression of NorA and QS system.

Novel benzothiazole‒urea hybrids: Design, synthesis and biological activity as potent anti-bacterial agents against MRSA

Novel benzothiazole‒urea hybrids were designed, synthesized and evaluated their anti-bacterial activity. They only exhibited anti-bacterial activity against Gram-positive bacteria, including clinical methicillin-resistant S. aureus (MRSA), compounds 5f, 5i, 8e, 8k and 8l exhibited potent activity (MIC = 0.39 and 0.39/0.78 μM against SA and MRSA, respectively). Crystal violet assay showed that compounds 5f, 8e and 8l not only inhibited the formation of biofilms but also eradicated preformed biofilms. Compound 8l had membrane disruption, little propensity to induce resistance, benign safety and in vivo anti-MRSA efficacy in a mouse model of abdominal infection. Therefore, our data demonstrated the potential to advance benzothiazole‒urea hybrids as a new class of antibiotics.

Novel FabI inhibitor disrupts the biofilm formation of MRSA through down-regulating the expression of quorum-sensing regulatory genes

OBJECTIVES

The aim of this study was to explore the antibiofilm and antivirulence efficacy of benzylaniline 4k against MRSA.

METHODS

The clinical MRSA strains were identified and used to evaluate their potential to form biofilm using crystal violet assay. The minimal inhibitory concentration (MIC) was determined using broth microdilution method. The expression of genes was detected using quantitative real-time PCR (qRT-PCR). Rabbit blood hemolytic assay was used to observe the inhibitory ability of alpha-hemolysin (Hla).

RESULTS

Compound 4k showed potent antibacterial activity against 16 clinical MRSA with an MIC₅₀ of 1.25 mg/L and MIC₉₀ of 2.25 mg/L. The value of minimum biofilm eradication concentration (MBEC) against MRSA2858 biofilm was of 1.5 mg/L, close to its MIC, superior to those of vancomycin and erythromycin. Compound 4k eradicated the formation of biofilm through inhibiting the gene expression of branched-chain fatty acid synthesis, down-regulating the expression of quorum-sensing (QS) regulatory genes (norA, agrA, icaA, hla), decreasing the level of hemolysis in a dose-dependent manner, and inhibiting rabbit blood hemolysis by 86.9% at a concentration of 1.25 mg/L. In a mouse model of abdominal infection, compound 4k was more effective than vancomycin in reducing bacterial load.

CONCLUSIONS

These results suggested that compound 4k could be developed as promising an anti-MRSA agent through affecting quorum-sensing system.

Fascaplysin derivatives binding to DNA via unique cationic five-ring coplanar backbone showed potent antimicrobial/antibiofilm activity against MRSA in vitro and in vivo

Methicillin-resistant Staphylococcus aureus (MRSA) is considered as one of the most dangerous clinical pathogens. Biofilms forming ability of MRSA is also a major cause of drug resistance. Hence, it is in urgent need to develop novel antibacterial/antibiofilm drugs. Fascaplysin with a unique cationic five-ring coplanar backbone is emerging as a potential antibacterial compound. In this study, aiming at developing novel and more effective agents, a series of fascaplysin derivatives and their corresponding β-carboline precursors have been synthesized. Then their antibacterial/antibiofilm activity and mechanisms against MRSA were investigated for the first time. The results showed that most fascaplysins rather than β-carboline precursors exhibit superior antimicrobial activity against MRSA ATCC43300, demonstrating the important role of cationic five-ring coplanar backbone playing in antibacterial activity. Among them, 14 and 18 are the most potent compounds with MIC value of 0.098 μg/ml (10-fold lower than vancomycin), and 18 featuring the lowest toxicity. Subsequent mechanisms exploration indicates that 18 has relatively stronger ability to destroy bacterial cell wall and membrane, higher binding affinity to bacterial genomic DNA. Molecular docking study revealed that besides the key role of cationic five-ring coplanar backbone, introduction of N-aryl amide at 9-position of fascaplysin promoted the combination of compound 18 and DNA via additional π-π stacking and hydrogen bonding of the naphthyl group. Moreover, fascaplysins could inhibit MRSA biofilm formation in vitro and bacterial infection in vivo. All these results illustrate that fascaplysin derivative 18 is a strong and safe multi-target antibacterial agent, which makes it an attractive candidate for the treatment of MRSA and its biofilm infections.

Inhibitory effects of two types of food additives on biofilm formation by foodborne pathogens

The inhibition of microbial biofilms is a significant concern in food safety. In the present study, the inhibitory effect of sodium citrate and cinnamic aldehyde on biofilm formation at minimum inhibitory concentrations (MICs) and sub-MICs was investigated for Escherichia coli O157:H7 and Staphylococcus aureus. The biofilm inhibition rate was measured to evaluate the effect of sodium citrate on S. aureus biofilms at 24, 48, 72, and 96 hr. According to the results, an antibiofilm effect was shown by both food additives, with 10 mg/ml of sodium citrate exhibiting the greatest inhibition of S. aureus biofilms at 24 hr (inhibition rate as high as 77.51%). These findings strongly suggest that sodium citrate exhibits a pronounced inhibitory effect on biofilm formation with great potential in the extension of food preservation and storage.