IN VITRO ANTIMICROBIAL ACTIVITY OF L-MALIC ACID-BASED COMPOSITION

The increasing prevalence of antimicrobial resistance has intensified the search for safe and effective alternatives to conventional antimicrobial agents, including natural compounds. L-malic acid, a naturally occurring in fruits and plant tissues, has attracted interest in this respect. The present study evaluated the in vitro antimicrobial activity of a formulation containing L-malic acid against reference strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans using a suspension assay. The tested formulation comprised 60% (w/w) L-malic acid, 30% (w/w) starch, and 10% (w/w) organosilica, obtained from product IONSIEVE MALOX®. The formulation was evaluated at nominal L-malic acid concentrations of 1, 2, and 3 mg·L-1 and exposure times of 1, 4, and 24 h using final inoculum levels of 5×10² or 1×10² CFU/mL. Under the tested conditions, the formulation reduced the number of recoverable cells of all examined microorganisms in a concentration-, time-, and inoculum-dependent manner. At 3 mg·L-1, no recoverable E. coli cells were detected after 1 h at 5×10² CFU/mL, whereas C. albicans reached undetectable levels after 4 h and P. aeruginosa and S. aureus after 24 h. At 1×10² CFU/mL no recoverable C. albicans cells were detected after 1 h, while in the other tested microorganisms - after 4 h. The formulations at 1 and 2 mg·L-1 also reduced recoverable counts of all tested strains, although with weaker early effects. These findings indicate that, under in vitro suspension-test conditions, L-malic acid exhibited significant antimicrobial activity against the tested bacterial and yeast strains and merit further investigation under application-relevant conditions.