Zhaoming Su

Identification of BfmR, a Response Regulator Involved in Biofilm Development, as a Target for a 2‑Aminoimidazole-Based Antibiofilm Agent

2-Aminoimidazoles (2AIs) have been documented to disrupt bacterial protection mechanisms, including biofilm formation and genetically encoded antibiotic resistance traits. Using Acinetobacter baumannii, we provide initial insight into the mechanism of action of a 2AI-based antibiofilm agent. Confocal microscopy confirmed that the 2AI is cell permeable, while pull-down assays identified BfmR, a response regulator that is the master controller of biofilm formation, as a target for this compound. Binding assays demonstrated specificity of the 2AI for response regulators, while computational docking provided models for 2AI-BfmR interactions. The 2AI compound studied here represents a unique small molecule scaffold that targets bacterial response regulators.

Evaluation of 4,5‐Disubstituted‐2‐Aminoimidazole–Triazole Conjugates for Antibiofilm/Antibiotic Resensitization Activity Against MRSA and Acinetobacter baumannii

A library of 4,5‐disubstituted‐2‐aminoimidazole–triazole conjugates (2‐AITs) was synthesized, and the antibiofilm activity was investigated. This class of small molecules was found to inhibit biofilm formation by methicillin‐resistant Staphylococcus aureus (MRSA) at low‐micromolar concentrations; 4,5‐disubstituted‐2‐AITs were also able to inhibit and disperse Acinetobacter baumannii biofilms. The activities of the lead compounds were compared against the naturally occurring biofilm dispersant cis‐2‐decenoic acid and were revealed to be more potent. The ability of selected compounds to resensitize MRSA to traditional antibiotics (resensitization activity) was also determined. Lead compounds were observed to resensitize MRSA to oxacillin by 2–4‐fold.

Structural studies on 4,5-disubstituted 2-aminoimidazole-based biofilm modulators that suppress bacterial resistance to β-lactams.

A library of 4,5‐disubstituted 2‐aminoimidazole triazole amide (2‐AITA) conjugates has been successfully assembled. Upon biological screening, this class of small molecules was discovered as enhanced biofilm regulators through non‐microbicidal mechanisms against methicillin‐resistant Staphylococcus aureus (MRSA) and multidrug‐resistant Acinetobacter baumannii (MDRAB), with active concentrations in the low micromolar range. The library was also subjected to synergism and resensitization studies with β‐lactam antibiotics against MRSA. Lead compounds were identified that suppress the antibiotic resistance of MRSA by working synergistically with oxacillin, a β‐lactam antibiotic resistant to penicillinase. A further structure–activity relationship (SAR) study on the parent 2‐AITA compound delivered a 2‐aminoimidazole diamide (2‐AIDA) conjugate with significantly increased synergistic activity with oxacillin against MRSA, decreasing the MIC value of the β‐lactam antibiotic by 64‐fold. Increased anti‐biofilm activity did not necessarily lead to increased suppression of antibiotic resistance, which indicates that biofilm inhibition and resensitization are most likely occurring via distinct mechanisms.

Membrane-Permeabilizing Activity of Reverse-Amide 2-Aminoimidazole Antibiofilm Agents Against Acinetobacter baumannii

Acinetobacter baumannii has quickly become one of the most insidious and prevalent nosocomial infections. Recently, the reverse-amide class of 2-aminoimidazole compounds (RA-2AI) was found both to prevent A. baumannii biofilm formation and also to disperse preexisting formations, putatively through interactions with cytosolic response regulators. Here we focus on how this class of antibiofilm agent traverses cellular membranes. Following the discovery of dosage-dependent growth rate changes, the cellular effects of RA-2AI were investigated using a combination of molecular assays and microscopic techniques. It was found that RA-2AI exposure has measureable effects on the bacterial membranes, resulting in a period of increased permeability and visible structural aberrations. Based on these results, we propose a model that describes how the structure of RA-2AI allows it to insert itself into and disrupt the fluidity of the membrane, creating an opportunity for increased molecular permeability.