Structure–Activity Relationship of Amino Acid Tunable Lipidated Norspermidine Conjugates: Disrupting Biofilms with Potent Activity against Bacterial Persisters

The emergence of bacterial resistance and biofilm associated infections has created a challenging situation in global health. In this present state of affairs where conventional antibiotics are falling short of being able to provide a solution to these problems, development of novel antibacterial compounds possessing the twin prowess of antibacterial and antibiofilm efficacy is imperative. Herein, we report a library of amino acid tunable lipidated norspermidine conjugates that were prepared by conjugating both amino acids and fatty acids with the amine functionalities of norspermidine through amide bond formation. These lipidated conjugates displayed potent antibacterial activity against various planktonic Gram-positive and Gram-negative bacteria including drug-resistant superbugs such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and β-lactam-resistant Klebsiella pneumoniae. This class of nontoxic and fast-acting antibacterial molecules (capable of killing bacteria within 15 min) did not allow bacteria to develop resistance against them after several passages. Most importantly, an optimized compound in the series was also capable of killing metabolically inactive persisters and stationary phase bacteria. Additionally, this compound was capable of disrupting the preformed biofilms of S. aureus and E. coli. Therefore, this class of antibacterial conjugates have potential in tackling the challenging situation posed by both bacterial resistance as well as drug tolerance due to biofilm formation

Chitosan Derivatives Active against Multidrug-Resistant Bacteria and Pathogenic Fungi: <i>In Vivo</i> Evaluation as Topical Antimicrobials

The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. Cationic chitosan derivatives, <i>N</i>-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure–activity relationship, activity toward drug-resistant bacteria and fungi, and mode of action are very rare. Moreover, toxicity and efficacy of these polymers under <i>in vivo</i> conditions are yet to be established. Herein, we investigated antibacterial and antifungal efficacies of the HTCC polymers against multidrug resistant bacteria including clinical isolates and pathogenic fungi, studied their mechanism of action, and evaluated cytotoxic and antimicrobial activities <i>in vitro</i> and <i>in vivo</i>. The polymers were found to be active against both bacteria and fungi (MIC = 125–250 μg/mL) and displayed rapid microbicidal kinetics, killing pathogens within 60–120 min. Moreover, the polymers were shown to target both bacterial and fungal cell membrane leading to membrane disruption and found to be effective in hindering bacterial resistance development. Importantly, very low toxicity toward human erythrocytes (HC₅₀ = >10000 μg/mL) and embryo kidney cells were observed for the cationic polymers <i>in vitro</i>. Further, no inflammation toward skin tissue was observed <i>in vivo</i> for the most active polymer even at 200 mg/kg when applied on the mice skin. In a murine model of superficial skin infection, the polymer showed significant reduction of methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) burden (3.2 log MRSA reduction at 100 mg/kg) with no to minimal inflammation. Taken together, these selectively active polymers show promise to be used as potent antimicrobial agents in topical and other infections