 Original Contribution ANALYSIS OF MICROBIAL CELL VIABILITY IN A LIQUID USING AN ACOUSTIC SENSOR TAGGEDPOLGA I. GULIY,* BORIS D. ZAITSEV, y SURYA K. MEHTA, z and IRINA A. BORODINA y TAGGEDEND * Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences Saratov, Russia; y Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Saratov, Russia; and z Mizoram University, Aizawl, India (Received 19 June 2019; revised 5 December 2019; in final from 6 December 2019) Abstract—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 mS/cm. Eontrol experiments were carried out with non-specific interac- tions 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 reso- nant peaks in the frequency dependence of the insertion loss of the sensor. The limit of cell detection was »10 2 10 3 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 solu- tions with conductivity in the range 4.530 mS/cm. (E-mail: guliy_olga@mail.ru) © 2019 World Federation for Ultrasound in Medicine & Biology. All rights reserved. Key Words: Acoustic sensor, Insertion loss of the sensor, Depth and frequency of resonant peaks, Microbial cells, Bacteriophages, Cell viability. INTRODUCTION Research on microbial contamination of water, food- stuffs and household articles is important for the timely prevention of food poisoning and mass disease. Various methods to evaluate microbial contamination are avail- able for use in the sanitary and bacteriologic control of surfaces in medical laboratories and food-processing facilities. Determining the viability of bacteria by assess- ing cell growth on nutrient agar (the so-called “gold standard”) is a routine and yet simple method used in microbiology laboratories. Determination of viability can be qualitative (whether colonies are formed) and quantitative (counting the number of viable cells in a sample) (Davey 2011). The classic method of assessing viability takes much time (no less than 24 h) and recog- nizes only those species that grow easily on nutrient media. The distinction between viability and death in the analysis of microbial cells is a complex and controversial problem, and even the gold standard method may not provide an accurate viability estimate (Vartoukian et al. 2010; Davey 2011). For example, lack of growth in cul- ture methods does not always mean the absence of living target cells and may be owing to a number of factors such as: (i) improperly selected culture medium (because many types of bacteria do not grow under artificial con- ditions; (ii) stress or damage to cells, leading to a dor- mant or damaged state; (iii) low density of the suspension, because of which no noticeable cell growth occurs; (iv) inhibition of target bacteria owing to the presence of bacteriocins of other bacteria in a mixed cul- ture (Vartoukian et al. 2010; Kumar and Ghosh 2019). Because the cultural diagnosis of bacteria has sev- eral disadvantages, alternative non-cultural methods for assessing cell viability are being developed (Kumar and Ghosh 2019). A variety of techniques have been devel- oped to assess cell survival, including the 3-(4,5- Address correspondence to: Olga I. Guliy, Institute of Biochem- istry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, Saratov 410049, Russia. E-mail: guliy_olga@mail.ru 1 ARTICLE IN PRESS Ultrasound in Med. & Biol., Vol. 00, No. 00, pp. 114, 2019 Copyright © 2019 World Federation for Ultrasound in Medicine & Biology. All rights reserved. Printed in the USA. All rights reserved. 0301-5629/$ - see front matter https://doi.org/10.1016/j.ultrasmedbio.2019.12.010