Investigation of Bacterial Growth Dynamics by the Physical Method of Turbidity

Author: Tamaz Mdzinarashvili
Co-authors: Irina Papukashvili1,2, Nino Shengelia1, Mariam Khvedelidze1
Keywords: Turbidity Methods, Bacterial Growth, Antimicrobial Agents, Mechanism of Infection
Annotation:

Continuous real-time observation of bacterial growth has a great advantage in detection and study of the mechanisms of various biologically active compounds interactions with the bacterial cell membrane. This approach gives us opportunity to measure the influence of antimicrobial drugs on the growth pattern of a bacterial colony. It can also help us to investigate early stages of bacteriophage-bacterial interaction, as these early stages define whether a bacteriophage infects a bacterial cell or not. We designed and created a method using a device which we built, that measures turbidity of liquid media and determines the number of bacteria with high precision. It is well known, that as the number of bacteria increases in liquid medium, the medium gets more turbid and with the method of turbidity it is possible to measure bacterial growth in a continuous real-time fashion. To study the process of bacterial growth, it is important to determine how the timing of bacterial growth changes in response to variability of composition of media, or if we introduce an antimicrobial drug or bacteriophage into the media. Using the method of turbidimetry, we showed that bacterial growth pattern is influenced not only by just presence of the antimicrobial drug, but also the concentration of the drug into the medium, as different concentrations of the drug showed different patterns of growth. We also showed that, the pattern and the speed of bacterial growth depends on the concentration of the liquid media (dilution of the standard medium). It is well known, that the concentration of antibiotics and bacteriophages in media are directly correlated to the inhibition of bacterial growth, conversely their very small amount is practically incapable of inhibiting the growth process. According to our results, if the proteins on the bacterial cell membrane are not fully saturated with antibiotics or bacteriophages and there are free unbound membrane proteins, the bacterial growth is not inhibited. If all antibiotic receptor proteins are occupied with drugs on the bacterial membrane surface, bacteria stops growth. In the case of bacteriophages, only after all receptor proteins are filled (about 103), phage starts the injection process of DNA into the bacterial cytoplasm.