## 1 Introduction  
Novel sensor technologies offer high-throughput and sensitive kinetic measurements on biomolecules and whole cells [1]. Traditionally, chemical and biochemical sensors are simply used to measure the concentration of a given analyte in an investigated sample. It was, however, then found that the novel sensor technologies could be used to investigate the deposition of particles [2, 3], and the formation of adsorbed protein layers [4, 5, 6, 7]. Further work led to the novel sensors being used to investigate cell adhesion and spreading [8, 9], and today, these novel sensors offer the possibility to investigate important biological processes in real time, in a completely label-free manner [10]. This possibility has already been found to have applications in research with mammalian cells. For example, basic adhesion processes and signaling events could be investigated with precision and sensitivity beyond the reach of traditional methods. Yet, these novel sensing technologies are still relatively unexploited in research and development involving bacterial cells. Bacteria are microscopic organisms showing different morphologies, including cylindrical (bacilli), spherical (cocci), comma-shaped (vibrio), and spiral-like (spirilla or spirochets), inter alia. They vary in size--typically 0.2-2 \(\upmu\)m in diameter and 3-5 \(\upmu\)m in length. Most bacteria have a cell wall providing shape and rigidity enveloping their lipid membrane. The cell wall consists of mainly peptidoglycan (PG), a polymer matrix comprising cross-linked chains of glucose derivatives, \(N\)-acetylglucosamine, and \(N\)-acetylmuramic acid. Bacteria that take up the dye crystal violet are called Gram-positive (after [PERSON] developed the staining technique in 1884) and if they do not, Gram-negative. Gram-positive bacteria have a much thicker PG layer. Pathogenic Gram-positive bacteria include _Streptococcus_, _Staphylococcus_, _Bacillus_, and _Clostridium_. Gram-negative have a thinner PG layer between inner and outer membranes, and in addition to proteins and phospholipids have lipopolysaccharidesaccharides (LPS) anchored into the outer membrane and projecting into the environment. LPS is made up of three different components: lipid A acting as an endotoxin, the O-antigen triggering an immune response in an infected host, and the core polysaccharide. Gram-negative bacteria cause many serious infections: _Neisseria gonorrhoeae_, _Neisseria meningitudes_, _Legionella_, _Haemophilus influenzae_, _Escherichia coli_, _Salmonella_, and _Shigella_ are a few examples of the pathogenic members of this class. Dielectric properties of _E. coli_ have been studied by a three-shell spheroidal model [11]. Based on the results of [PERSON] et al., the specific capacitance of the inner membrane is 0.6-0.7 \(\upmu\)F/cm\({}^{2}\)[11]. The conductivity of the periplasmic space is 2.2-3.2 S/m, and the relative permittivity and the conductivity of the cytoplasm are approximately 100 and 0.22 S/m, respectively [11]. In the study by [PERSON], the periplasmic space was found to increase with the square root of the medium ionic strength and they showed that heat treatment of the cells leads to a reduction of cytoplasmic conductivity to 0.9 mS/cm, likely due to the efflux of ions through the permeabilized inner membrane, measured by electrorotation [12]. Some bacteria--belonging to the phylum Tenericutes--lack a cell wall; many members of this phylum are pathogens. Myobacterial belong to the diverse family of Actinobacteria and the main components of their cell wall are the PG layer, mycolic acid, and arabin-galactan. Myobacterial are Gram-positive organisms, but their envelopes share notable features with Gram-negative cell walls, having a thin PG layer and an outer permeability barrier acting as a pseudo-outer membrane [13; 14]. Bacterial cell wall components are promising targets for antibiotic/antimicrobial compound discovery. Gram-positive and Gram-negative bacteria respond to different antibiotics and antimicrobial drugs.