The objective of this paper is to present a new class of polylactic acid (PLA) fibers containing cobalt-based metal organic frameworks (MOF). The material used was Co-SIM-1, a cobalt-based substituted imidazolate. Composite mats were prepared by electrospinning PLA with a suspension of polyvinylpyrrolidone-stabilized Co-SIM-1. MOF particles formed aggregate of a small number of primary particles that, after electrospun, became completely embedded inside polymeric fibers. The dispersion of particles was better for lower loadings, for which the relative amount of metal released to culture media was also higher. The antimicrobial activity of composite mats was assessed using SEM images, fluorescence microscopy, direct plate reading of fluorescent stains and plate count of colony forming units among other. The microorganisms used in this study were Pseudomonas putida and Staphylococcus aureus. Fluorescence techniques allowed recording viable and damaged cells directly on mat surface and in the culture media embedding the fibers. The results showed higher sensitivity of S. aureus to cobalt-containing fibers, with a reduction in colony forming units of up to 60% with respect to PLA mats. The results also showed the presence of viable but non-culturable microorganisms, which fail to form colonies but yield a positive signal to viable cell staining. Cobalt-based MOF included in electrospun mats provide antibacterial activity suitable to be used to prepare membranes for various biomedical applications. (C) 2014 Elsevier B.V. All rights reserved.