Bacterial synthesis parameters and antibacterial mechanisms of titanium dioxide nanoparticles against multidrug resistant Gram-negative pathogens

Gram-negative multidrug-resistant (MDR) pathogens, including Pseudomonas aeruginosa , Klebsiella pneumoniae , Acinetobacter baumannii , and Escherichia coli , represent an escalating global health threat, with mortality projected to reach 10 million deaths annually by 2050. Bacterially synthesized titanium dioxide nanoparticles (TiO₂NPs) have emerged as a promising antimicrobial strategy; however, no study has systematically correlated microbial biosynthesis parameters such as bacterial species, precursor type and concentration, pH, temperature, and incubation time, with nanoparticle properties and their efficacy against MDR Gram-negative bacteria. This review critically evaluates the green synthesis of TiO₂NPs across more than 25 microbial species, with emphasis on how synthesis conditions influence nanoparticle size, morphology, and stability. It further examines the underlying antimicrobial mechanisms, including reactive oxygen species (ROS) generation, membrane disruption, and DNA damage. In addition, the role of biosurfactants in nanoparticle stabilization is discussed, alongside key challenges hindering clinical translation, particularly the lack of standardized synthesis protocols and limited in vivo safety data. By integrating biosynthesis parameters with antimicrobial performance, this review provides a focused framework for advancing TiO₂NPs as sustainable alternatives to conventional antibiotics against drug-resistant Gram-negative pathogens.