Comparative Analysis of UV Irradiation Effects on Escherichia coli and Pseudomonas aeruginosa Bacterial Cells Utilizing Biological and Computational Approaches.

Microorganisms have a large number of tools to withstand different, and sometimes strong, environmental stresses, including irradiation, but this ability should be further evaluated for certain applications. Growth inhibition and morphological alterations of Escherichia coli M-17 and Pseudomonas aeruginosa GRP3 wild-type cells caused by UV-A irradiation have been detected in the present study. Comparative analysis was carried out using well-established microbiological methods (determination of specific growth rate, growth lag phase duration, and colony-forming unit number-CFU) and computational approaches, employing light microscopy and digital image analysis to evaluate bacterial cell morphology. Decreases in the specific growth rate, prolonged lag-phases, and lowered CFUs were observed after 5 and 10 min of UV irradiation (approx. 40 Gy) compared to the control (nonirradiated) cells. Accordingly, two computational parameters-the average bacterial cell surface area and the bacterial cell perimeter (i.e., of the 2D projection of bacterial cells in microscopy image)-were reduced. The ratio of bacterial cell surface area (S) to the square of the perimeter (p (2) ) was reduced after 5 min of irradiation, but after 10 min of irradiation the studied bacterial cells became flat cylinders. The revealed findings are concluded to be highly useful in developing new, rapid analysis methods to monitor environmental and UV irradiation effects on bacteria and to detect bacterial cell morphology alterations.