Comparative evaluation of alternative therapies against oral opportunistic microorganisms: an in vitro study

Abstract

Introduction: Opportunistic Gram-negative microorganisms such as Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa may colonize the oral cavity and contribute to hospital-acquired infections, particularly in critically ill patients. Alternative strategies to chlorhexidine have been investigated for controlling these pathogens. Methods: This in vitro experimental study was conducted at the Federal University of Rio Grande do Norte. Strains of A. baumannii, K. pneumoniae, and P. aeruginosa were tested against the probiotic Lacticaseibacillus rhamnosus (PLR), antimicrobial photodynamic therapy (aPDT; methylene blue + 660 nm laser), and the hydroethanolic extract of Spondias mombin L. (SME), using 0.12% chlorhexidine (CHX) as a positive control. Outcomes included bacterial growth inhibition, anti-adherent activity, and antibiofilm effects. Data were analyzed using ANOVA and Tukey’s test (p < 0.05). Results: PLR inhibited all tested microorganisms and showed no significant difference compared with CHX for A. baumannii and K. pneumoniae (p > 0.05). aPDT demonstrated greater anti-adherent activity against K. pneumoniae (p < 0.05), whereas PLR showed superior performance against P. aeruginosa (p < 0.05), both comparable to CHX. Significant differences were observed among groups in monospecies biofilms (p < 0.05), although PLR did not differ from CHX. In multispecies biofilms, PLR exhibited activity equivalent to the positive control. Conclusions: PLR and aPDT effectively controlled microbial growth, with PLR demonstrating antimicrobial, anti-adherent, and antibiofilm effects comparable to chlorhexidine, supporting its potential clinical application.