Combinatorial Antibacterial Activity of Allium sativum (Garlic) with Titanium Dioxide (TiO?) and Zinc Oxide (ZnO) Nanoparticles against Selected Bacterial Isolates from a University Hostel Wastewater in Oyo, Nigeria

Abstract

Researchers are looking into new ways to fight bacteria because antibiotics are becoming less effective. This has sparked interest in phytochemical agents and metal oxide nanomaterials as substitutes for antimicrobial strategies. This study examined the individual and combined antibacterial effect of extracts of red garlic (RG) and white garlic (WG) (Allium sativum) with zinc oxide (ZnO) and titanium dioxide (TiO?) nanoparticles against bacteria isolated from university hostel wastewater. Wastewater samples were collected aseptically from two female hostels at Ajayi Crowther University, Oyo, Nigeria. Bacterial isolates were characterised by morphological and biochemical methods, and antibiotic susceptibility was profiled by Kirby-Bauer disc diffusion method following Clinical and Laboratory Standards Institute (CLSI, 2022) guidelines. We assessed the antibacterial activity using the agar well diffusion and disc methods. Data analysis was carried out by one-way ANOVA followed by the Tukey honest significant difference (HSD) test (p < 0.05). A total of eight isolates were identified, namely Bacillus cereus (50%), Escherichia coli (25%), Pseudomonas aeruginosa (12.5%), and Staphylococcus aureus (12.5%). Ethanol extracts produced larger zones of inhibition (Zoo) than aqueous extracts across all treatment combinations (p < 0.001). Combinations containing ZnO led to zones of inhibition (ZoI) up to 24 mm, while similar combinations with TiO? reached 22 mm. The combination of RG and TiO? in aqueous solution had the maximum ZoI on Pseudomonas aeruginosa (22 mm). Escherichia coli was the organism more resistant to individual and aqueous garlic preparations. At least one combination of ethanol agar wells achieved CSI ‘Susceptible’ threshold of 13 mm for all isolates. The synergy of Garlic-ZnO exhibits significant antibacterial activity against pathogens from wastewater, which advocates further studies on minimum inhibitory concentrations, biofilm disruption, and in-vivo safety.