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In Vitro and In Vivo Antibacterial and Antibiofilm Activity of Zinc Sulfate (ZnSO4) and Carvacrol (CV) Alone and in Combination with Antibiotics Against Pseudomonas aeruginosa

Melika Moradi, Effat Abbasi Montazeri, Sirous Rafiei Asl, Ali Pormohammad, Zahra Farshadzadeh, Dian Dayer, Raymond Joseph Turner

Antibiotics, 2025

12 citations

Abstract

Background/Objectives: Biofilm-embedded bacteria, such as Pseudomonas aeruginosa (P. aeruginosa), are highly resistant to antibiotics, making their treatment challenging. Plant-based natural compounds (PBCs) and metal(loid)-based antimicrobials (MBAs) are promising alternatives. This study evaluated the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and synergistic effects of zinc sulfate (ZnSO4), carvacrol (CV), and antibiotics (ciprofloxacin [CIP], tobramycin [TOB], and azithromycin [AZM]) against P. aeruginosa PAO1. Methods: The MIC and MBC of ZnSO4, CV, and antibiotics were determined using a 96-well plate method. Cytotoxicity was assessed via MTT assay. Fractional inhibitory concentration (FIC), fractional bactericidal concentration (FBC), minimal biofilm inhibition concentration (MBIC), and minimum biofilm eradication concentration (MBEC) indices were calculated for each combination of agents. Checkerboard assays identified interactions, and the effectiveness of combinations was further evaluated in a mouse chronic lung infection model with treatments delivered intratracheally, intraperitoneally, and orally. Results: TOB had the lowest MIC and MBC values, proving most effective against P. aeruginosa PAO1. Strong synergy was observed with CV + ZnSO4 (CV + Zn) combined with CIP, CV with CIP, and CV + Zn with TOB, as indicated by low FIC indices. CV + Zn with TOB and CV with TOB had low FBC indices, while CV + Zn with AZM showed…

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