Composite i-PP/PEDOT films made of isotactic polypropylene (i-PP), which is frequently used for the fabrication of implantable medical devices for internal use, and chemically synthesized poly(3,4-ethylendioxythiophene) (PEDOT) nanoparticles, which are electroactive and biocompatible, have been prepared and used to detect bacterial metabolism. After chemical and morphological characterization, the properties (interfacial, mechanical, thermal, and electrochemical) and biocompatibility of i-PP/PEDOT have been examined. Besides, carbon screen-printed electrodes coated with i-PP/PEDOT have been found to detect the growth of Gram-positive and Gram-negative bacteria through the oxidation of nicotinamide adenine dinucleotide (NADH), which arises from the metabolism of bacteria (i.e., respiration). Thus, as outer bacterial membranes are permeable to cytosolic NADH, this metabolite has been found to be an appropriate target for the detection of bacterial proliferation. In addition, the sensor does not respond to eukaryotic cells. This is because the major NADH pool in eukaryotic cells is located at the mitochondria and, therefore, the concentration of NADH in the medium is not high enough to be detected since the inner mitochondrial membrane is impermeable to NADH or NAD+.