Antimicrobial peptides (AMPs) are being explored as a potential solution to combat antibiotic resistance, as they have shown promise in reducing susceptibility to antibiotics. This study explores if [R4W4] peptide is bacteriostatic or bactericidal using modified two-fold serial dilution and evaluates synergism of gentamicin and [R4W4] against Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA) by checkered board assay. The MRSA resistant to [R4W4] and possibility with other antibiotics was evaluated with serial passage. Moreover, we investigated the mechanism of action of [R4W4] against MRSA by applying biophysical assays to evaluate zeta potential, cytoplasmic membrane depolarization, and Lipoteichoic acid (LTA) binding affinity. [R4W4] exhibits bactericidal activity against bacterial isolates (MBC/MIC £ 4), with a synergistic effect with gentamicin against E. coli (FICI=0.3), but not against MRSA (FICI=0.75). [R4W4] at 16 µg/ml concentration stabilizes the zeta potential of MRSA -33 ± 0.88 mV to -8.37 mV. Also, [R4W4] at 2 x MIC and 16 x MIC revealing a membrane perturbation process associated with concentration-dependent effects. Lastly, in the presence of BODIPY-Cadaverine fluorescence dyes, [R4W4] reveals binding affinity to LTA comparable with melittin, the positive control. In addition, a change in the antibacterial activity of [R4W4] against MRSA in the absence and presence of LTA did not change the MIC 8µg/ml. Therefore, the [R4W4] mechanism of action is bactericidal with the potential to interact with bacterial cell membranes, causing concentration-dependent cytoplasm membrane perturbation.
","abstract_html":"<p>Antimicrobial peptides (AMPs) are being explored as a potential solution to combat antibiotic resistance, as they have shown promise in reducing susceptibility to antibiotics. This study explores if [R<sub>4</sub>W<sub>4</sub>] peptide is bacteriostatic or bactericidal using modified two-fold serial dilution and evaluates synergism of gentamicin and [R<sub>4</sub>W<sub>4</sub>] against <em>Escherichia coli</em> (<em>E. coli)</em> and Methicillin-resistant <em>Staphylococcus aureus</em> (MRSA) by checkered board assay. The MRSA resistant to [R<sub>4</sub>W<sub>4</sub>] and possibility with other antibiotics was evaluated with serial passage. Moreover, we investigated the mechanism of action of [R<sub>4</sub>W<sub>4</sub>] against MRSA by applying biophysical assays to evaluate zeta potential, cytoplasmic membrane depolarization, and Lipoteichoic acid (LTA) binding affinity. [R<sub>4</sub>W<sub>4</sub>] exhibits bactericidal activity against bacterial isolates (MBC/MIC £ 4), with a synergistic effect with gentamicin against <em>E. coli</em> (FICI=0.3), but not against MRSA (FICI=0.75). [R<sub>4</sub>W<sub>4</sub>] at 16 µg/ml concentration stabilizes the zeta potential of MRSA -33 ± 0.88 mV to -8.37 mV. Also, [R<sub>4</sub>W<sub>4</sub>] at 2 x MIC and 16 x MIC revealing a membrane perturbation process associated with concentration-dependent effects. Lastly, in the presence of BODIPY-Cadaverine fluorescence dyes, [R<sub>4</sub>W<sub>4</sub>] reveals binding affinity to LTA comparable with melittin, the positive control. In addition, a change in the antibacterial activity of [R<sub>4</sub>W<sub>4</sub>] against MRSA in the absence and presence of LTA did not change the MIC 8µg/ml. Therefore, the [R<sub>4</sub>W<sub>4</sub>] mechanism of action is bactericidal with the potential to interact with bacterial cell membranes, causing concentration-dependent cytoplasm membrane perturbation.</p>","abstract_has_math":false,"creators":["Akinwale, Ajayi"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Pharmaceutical Sciences","degree_department":null,"school":null,"contributors":["Jason Yamaki","Rakesh Tiwari","Ahmed Aftab","Keykavous Parang"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-05-01T07:00:00Z","date_published":"2024-05-01T07:00:00Z","updated_at":"2026-07-24T01:38:37Z","subjects":["Antimicrobial peptides","Methicillin-resistant Staphylococcus aureus","Mechanism of action","Antimicrobial Cyclic Peptide [R4W4]","Other Pharmacy and Pharmaceutical Sciences","Pharmaceutics and Drug Design"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://digitalcommons.chapman.edu/pharmaceutical_sciences_dissertations/36","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Jason Yamaki","Rakesh Tiwari","Ahmed Aftab","Keykavous Parang"]},{"key":"dc:creator","label":"Author","values":["Akinwale, Ajayi"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2026-05-16T07:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Pharmaceutical Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Antimicrobial peptides","Methicillin-resistant Staphylococcus aureus","Mechanism of action","Antimicrobial Cyclic Peptide [R4W4]","Other Pharmacy and Pharmaceutical Sciences","Pharmaceutics and Drug Design"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://digitalcommons.chapman.edu/pharmaceutical_sciences_dissertations/36"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Antimicrobial peptides (AMPs) are being explored as a potential solution to combat antibiotic resistance, as they have shown promise in reducing susceptibility to antibiotics. This study explores if [R4W4] peptide is bacteriostatic or bactericidal using modified two-fold serial dilution and evaluates synergism of gentamicin and [R4W4] against Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA) by checkered board assay. The MRSA resistant to [R4W4] and possibility with other antibiotics was evaluated with serial passage. Moreover, we investigated the mechanism of action of [R4W4] against MRSA by applying biophysical assays to evaluate zeta potential, cytoplasmic membrane depolarization, and Lipoteichoic acid (LTA) binding affinity. [R4W4] exhibits bactericidal activity against bacterial isolates (MBC/MIC £ 4), with a synergistic effect with gentamicin against E. coli (FICI=0.3), but not against MRSA (FICI=0.75). [R4W4] at 16 µg/ml concentration stabilizes the zeta potential of MRSA -33 ± 0.88 mV to -8.37 mV. Also, [R4W4] at 2 x MIC and 16 x MIC revealing a membrane perturbation process associated with concentration-dependent effects. Lastly, in the presence of BODIPY-Cadaverine fluorescence dyes, [R4W4] reveals binding affinity to LTA comparable with melittin, the positive control. In addition, a change in the antibacterial activity of [R4W4] against MRSA in the absence and presence of LTA did not change the MIC 8µg/ml. Therefore, the [R4W4] mechanism of action is bactericidal with the potential to interact with bacterial cell membranes, causing concentration-dependent cytoplasm membrane perturbation.
"]},{"key":"dc:source","label":"Dc Source","values":["Akinwale, AD. Mechanistic Study of Antimicrobial Cyclic Peptide [R4W4] Antibacterial Effectiveness against Methicillin-resistant Staphylococcus aureus (MRSA). [dissertation]. Irvine, CA: Chapman University; 2024. https://doi.org/10.36837/chapman.000580"]},{"key":"dc:title","label":"Title","values":["Mechanistic Study of Antimicrobial Cyclic Peptide [R4W4] Antibacterial Effectiveness against Methicillin-resistant Staphylococcus aureus (MRSA)"]}]}],"canonical_facts":{"dc:contributor":["Jason Yamaki","Rakesh Tiwari","Ahmed Aftab","Keykavous Parang"],"dc:creator":["Akinwale, Ajayi"],"dc:date.available":["2026-05-16T07:00:00Z"],"dc:description.abstract":["Antimicrobial peptides (AMPs) are being explored as a potential solution to combat antibiotic resistance, as they have shown promise in reducing susceptibility to antibiotics. This study explores if [R4W4] peptide is bacteriostatic or bactericidal using modified two-fold serial dilution and evaluates synergism of gentamicin and [R4W4] against Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA) by checkered board assay. The MRSA resistant to [R4W4] and possibility with other antibiotics was evaluated with serial passage. Moreover, we investigated the mechanism of action of [R4W4] against MRSA by applying biophysical assays to evaluate zeta potential, cytoplasmic membrane depolarization, and Lipoteichoic acid (LTA) binding affinity. [R4W4] exhibits bactericidal activity against bacterial isolates (MBC/MIC £ 4), with a synergistic effect with gentamicin against E. coli (FICI=0.3), but not against MRSA (FICI=0.75). [R4W4] at 16 µg/ml concentration stabilizes the zeta potential of MRSA -33 ± 0.88 mV to -8.37 mV. Also, [R4W4] at 2 x MIC and 16 x MIC revealing a membrane perturbation process associated with concentration-dependent effects. Lastly, in the presence of BODIPY-Cadaverine fluorescence dyes, [R4W4] reveals binding affinity to LTA comparable with melittin, the positive control. In addition, a change in the antibacterial activity of [R4W4] against MRSA in the absence and presence of LTA did not change the MIC 8µg/ml. Therefore, the [R4W4] mechanism of action is bactericidal with the potential to interact with bacterial cell membranes, causing concentration-dependent cytoplasm membrane perturbation.
"],"dc:identifier":["https://digitalcommons.chapman.edu/pharmaceutical_sciences_dissertations/36"],"dc:source":["Akinwale, AD. Mechanistic Study of Antimicrobial Cyclic Peptide [R4W4] Antibacterial Effectiveness against Methicillin-resistant Staphylococcus aureus (MRSA). [dissertation]. Irvine, CA: Chapman University; 2024. https://doi.org/10.36837/chapman.000580"],"dc:subject":["Antimicrobial peptides","Methicillin-resistant Staphylococcus aureus","Mechanism of action","Antimicrobial Cyclic Peptide [R4W4]","Other Pharmacy and Pharmaceutical Sciences","Pharmaceutics and Drug Design"],"dc:title":["Mechanistic Study of Antimicrobial Cyclic Peptide [R4W4] Antibacterial Effectiveness against Methicillin-resistant Staphylococcus aureus (MRSA)"],"thesis:degree_discipline":["Pharmaceutical Sciences"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T01:38:37Z"}