No abstract

Inappropriate and uncontrolled use of antibiotics results in the emergence of antibiotic resistance, thereby threatening the present clinical regimens to treat infectious diseases. Therefore, new antimicrobial agents that can prevent bacteria from developing drug resistance are urgently needed. Selective disruption of bacterial membranes is the most effective strategy for combating microbial infections as accumulation of genetic mutations will not allow for the emergence of drug resistance against these antimicrobials. In this work, we tested cholic acid (CA) derived amphiphiles tethered with different alkyl chains for their ability to combat Gram-positive bacterial infections. In-depth biophysical and biomolecular simulation studies suggested that the amphiphile with a hexyl chain (6) executes more effective interactions with Gram-positive bacterial membranes as compared to other hydrophobic counterparts. Amphiphile 6 is effective against multidrug resistant Gram-positive bacterial strains as well and does not allow the adherence of S. aureus on amphiphile 6 coated catheters implanted in mice. Further, treatment of wound infections with amphiphile 6 clears the bacterial infections. Therefore, the current study presents strategic guidelines in design and development of CA-derived membrane-targeting antimicrobials for Gram-positive bacterial infections.

Infections caused by fungal species via their existence as biofilms on medical devices can cause organ damage via candidiasis and candidemia. Different Candida species like Candida albicans can pose a serious threat by resisting host's immune system and by developing drug resistance against existing antimycotic agents. Therefore, targeting of fungal membranes can be used as an alternative strategy to combat the fungal infections. Here, we present screening of different amphiphiles based on cholic acid against different Candida strains as these amphiphiles can act as potent membrane-targeting antimycotic agents. Structure−activity correlations, biochemical assays and electron microscopy studies showed that amphiphiles having 4 and 6 carbon chains are most potent, safe and can act on the fungal membranes. Candida albicans did not show emergence of drug resistance on repeated usage of these amphiphiles unlike fluconazole. We show that these amphiphiles can prevent the formation of biofilms and also have the ability to degrade preformed biofilms on different substrates including acrylic teeth. We further demonstrate that amphiphiles 4 and 6 can clear the Candida albicans wound infections and prevent the biofilm formation on indwelling devices in murine models. Therefore, amphiphiles derived from cholic acid and their coatings provide suitable alternatives for inhibiting the fungal infections.

Emergence of vancomycin resistance in Gram-positive bacteria and the prevalence of vancomycin-resistant Enterococci (VRE) infections are highly alarming as very limited antibiotic options are available against VRE infections. Here, we present the synthesis of cholic acid-derived dimeric amphiphiles where two cholic acid moieties are tethered through carboxyl terminals using different alkylene spacers. Our investigations revealed that dimer 5 possessing a propylene spacer and glycine-valine peptides tethered on hydroxyl groups is the most effective antimicrobial against VRE. Dimer 5 can permeabilize bacterial membranes, generate reactive oxygen species, and clear preformed biofilms. We further demonstrate that dimer 5 downregulates vancomycinmediated transcriptional activation of the vanHAX gene cluster and does not allow VSE to develop vancomycin resistance until 100 generations. Therefore, this study, for the first time, presents a bacterial membrane-targeting amphiphile that can mitigate VRE infections and inhibit the emergence of vancomycin resistance.

Tuberculosis (TB), including extrapulmonary TB, is responsible for more than one million deaths in a year worldwide. Existing methods of mycobacteria detection have poor sensitivity, selectivity, and specificity, especially in human tissues. Herein, the synthesis of a cholic acid‐derived fluorescent probe (P4) that can specifically stain the mycobacterium species is presented. It is shown that P4 probe specifically binds with mycobacterial lipids, trehalose monomycolate, and phosphatidylinositol mannoside 6. P4 probe can detect mycobacteria in polymicrobial planktonic cultures and biofilms with high specificity, selectivity, and sensitivity. Moreover, it can detect a single mycobacterium in the presence of 10 000 other bacilli. Unlike the probes that depend on active mycobacterial enzymes, the membrane‐specific P4 probe can detect mycobacteria even in formalin‐fixed paraffin‐embedded mice and human tissue sections. Therefore, the ability of the P4 probe to detect mycobacteria in different biological milieu makes it a potential candidate for diagnostic and prognostic applications in clinical settings.