Investigation of the growth kinetics of Streptococcus mutans bacteria on Zr-C coating surfaces deposited on 316L stainless steel substrates

Purpose: The conducted research aims to describe the kinetics of Streptococcus mutans bacteria growth on the surface of Zr-C coatings with varying carbon content deposited on 316L medical-grade stainless steel substrates. Design/methodology/approach: The coatings were deposited using the MS PVD (Magnetron Sputtering Physical Vapour Deposition) technique at a constant temperature of 400°C. Varying carbon contents in the coatings were achieved by changing the flow rate of acetylene during the process. The dynamics of bacteria growth cultivated at 37°C were examined on the surface of the coatings for incubation times ranging from 0 to 72 hours. Generalised logistic functions were utilised for the mathematical description of the obtained results. Findings: The produced coatings exhibited varying carbon content, determining the structural composition ranging from a mixture of metallic Zr and ZrC through stoichiometric zirconium carbide to nanocrystalline grains of ZrC in an amorphous carbon matrix. The obtained results unequivocally demonstrate that in the case of ZrC coatings, the carbon content influences both the bacterial growth rate during the proliferation phase and the final population of bacteria. Research limitations/implications: In the conducted research on bacterial population dynamics, only a single strain of Streptococcus mutans was considered, and the mathematical description was limited to reaching a pseudo-steady state by the population. Practical implications: The proposed model can successfully be adapted to describe the dynamics of other individual strains of bacteria dwelling on metallic surfaces as well as coatings. Originality/value: The proposed model can serve as a tool for studying, among other things, inflexion points of logistic curves, which are considered as the boundary between the dominance of anabolic and catabolic processes in the bacterial population.