Topical Delivery of Autochthonous Lactic Acid Bacteria Using Calcium Alginate Microspheres as a Probiotic Carrier...

Background/Objectives: Three distinct strains of lactic acid bacteria (LAB), isolated from naturally fermented bread sourdough and representing the local autochthonous microflora, were selected to evaluate their potential probiotic properties. In addition, we evaluated whether these strains could be used in topical formulations. Methods: We evaluated probiotic properties such as the ability to co-aggregate with pathogens, antimicrobial activity, inhibition of pathogenic biofilms, and ability to adhere to human keratinocyte cells. Further, bacteria were encapsulated in calcium alginate microspheres using the emulsification/external gelation method, and their viability in topical formulations was assessed. Results: LAB significantly inhibited biofilm formation by the tested pathogens with complete inhibition observed in certain cases. The strength and specificity of these probiotic effects varied depending on the LAB strain and the target pathogen. Furthermore, among the tested strains, L. reuteri 182 exhibited the highest adhesion rates, reaching 77.94 ± 1.84%. In the context of potential topical applications, the preservative present in the formulation completely inactivated the planktonic cells of L. reuteri 182. In contrast, encapsulation within a biopolymeric system conferred protection against the preservative's bactericidal effect. After 35 days of storage at room temperature, viable cell counts reached 5.94 ± 0.06 lg CFU/g. Conclusions: Our findings confirm that local LAB strains, specifically L. reuteri 182 and L. plantarum F1, possess essential probiotic characteristics and can be effectively incorporated into preservative-containing topical formulations via efficient encapsulation strategies. This underscores the potential of these topical probiotics for skin health and highlights the need for clear regulatory guidance to ensure their safe and effective application.