Use of an optical sensor to directly monitor the metabolic activity of growing bacteria.

The metabolic activity of growing bacteria was directly monitored by using an electro-optical (EO) sensor. The sensor enables examination of bacteria in batch and continuous cultures. As examples, we report studies with Еscherichia coli, a bacterium with an aerobic type of metabolism, and Lactobacillus plantarum, a bacterium with an anaerobic type of metabolism. Bacterial growth was accompanied by a simultaneous change in both the hydrodynamic mean size (HMS) of the bacteria and the concentration of ions in the cytoplasm (CIC). Both variables were associated with the regulation of cellular metabolic activity, which can be cyclic during intense bacterial growth. A simultaneous change in metabolic activity and osmotic regulation was also found. For СIC and HMS measurements, we used online results of the EO analysis of cells suspended in water. The measured results for the CIC and HMS can be used to directly monitor bacterial metabolism. The results of this study are of practical importance for the real-time EO monitoring of the metabolic activity of growing bacteria without preliminary sample preparation.

Analysis of Microbial Cell Viability in a Liquid Using an Acoustic Sensor.

A method was developed for the rapid analysis and evaluation of the viability of bacteriophage-infected Escherichia coli (E.coli) XL-1 directly in a conducting suspension by using a slot-mode sensor. The method is based on recording the changes in the depth and frequency of resonant absorption peaks in the frequency dependence of the insertion loss of the sensor before and after the biologic interaction of E. coli with specific bacteriophages. The possibility was shown of recording the infection of E. coli with specific bacteriophages and assessing its viability in suspensions with a conductivity of 4.5-30 µS/cm. Сontrol experiments were carried out with non-specific interactions of E. coli cells with bacteriophages, in which no changes in the sensor variables were observed. The optimal informational variable for estimating the number of viable cells was the degree of change in the depth of the resonant peaks in the frequency dependence of the insertion loss of the sensor. The limit of cell detection was ∼102-103 cells mL-1, with an analysis time of about 5 min. An additional advantage of the sensor was the availability of a removable liquid container, which allows one to use it repeatedly and to facilitate the cleaning of the container from spent samples. The results are promising for the detection of bacteria and assessment of their viability in solutions with conductivity in the range 4.5-30 µS/cm.