A composite medium enabling co-culture of Lactobacillus spp. and Pseudomonas aeruginosa with application to surface growth studies.

Investigation of interbacterial antagonism in mixed cultures requires cultivation conditions that support the growth of physiologically distinct microorganisms. Standard systems often favor one interaction partner and distort observed outcomes, particularly during co-cultivation of Gram-positive and Gram-negative bacteria. Lactobacillus spp. are commonly cultivated in De Man, Rogosa and Sharpe (MRS) medium, whereas Pseudomonas aeruginosa grows optimally in Luria-Bertani (LB) or nutrient broth. These media do not permit balanced co-cultivation and may suppress characteristic phenotypic traits associated with surface attachment of P. aeruginosa. This article describes a composite liquid medium formulated by combining MRS broth with LB (Lennox modification) or nutrient broth in a defined volumetric ratio. The formulation enables co-cultivation of Pseudomonas aeruginosa and Lactobacillus spp. under static conditions while supporting surface-associated growth and qualitative assessment of quorum sensing-linked phenotypes. The method provides a standardized in vitro tool for studying interactions and growth mode transitions in mixed bacterial cultures. The method can be applied for in vitro screening of antagonistic or quorum sensing-modulating effects in mixed bacterial cultures.•Composite liquid medium for co-cultivation of pathogenic and probiotic bacteria•Support of surface-associated growth and quorum sensing-linked phenotypes in Pseudomonas aeruginosa•Reproducible in vitro framework for studying interspecies antagonism․.