Effect of air drying on bacterial viability: A multiparameter viability assessment

• Published in: Journal of microbiological methods 2012-08, Vol.90 (2), p.86-95
• Main Authors: Nocker, Andreas, Fernández, Priscilla Sossa, Montijn, Roy, Schuren, Frank
• Format: Article
• Language: English
• Subjects: Air; air drying; Biological and medical sciences; Cell Membrane - physiology; Colony Count, Microbial; Culture Media; Desiccation; Desiccation - methods; Enterococcus hirae; Escherichia coli; esterases; Esterases - metabolism; Extracellular polysaccharides; fluorescence; fluorescent dyes; Fluorescent Dyes - metabolism; Freeze drying; Fundamental and applied biological sciences. Psychology; Gram-negative bacteria; Gram-Negative Bacteria - enzymology; Gram-Negative Bacteria - growth & development; Gram-Negative Bacteria - metabolism; Gram-Negative Bacteria - physiology; Gram-positive bacteria; Gram-Positive Bacteria - enzymology; Gram-Positive Bacteria - growth & development; Gram-Positive Bacteria - metabolism; Gram-Positive Bacteria - physiology; industrial applications; Magnesium chloride; membrane potential; Membrane Potentials; Microbial Viability; Microbiology; Oxidation-Reduction; plate count; Pseudomonas aeruginosa; public health; Real time viability (RTV) assay; Staining and Labeling - methods; Staphylococcus aureus; Viability
• ISSN: 0167-7012; 1872-8359
• DOI: 10.1016/j.mimet.2012.04.015

The effect of desiccation on the viability of microorganisms is a question of great interest for a variety of public health questions and industrial applications. Although viability is traditionally assessed by plate counts, cultivation-independent methods are increasingly applied with the aim to gain more insight into why cells might not form colonies and to optimize production processes. To evaluate their usefulness, we applied in this study a multiparameter viability assay to selected bacteria (Escherichia coli, Pseudomonas aeruginosa, Enterococcus hirae, and Staphylococcus aureus) subjected to air-drying in the absence or presence of supplements. Tests included growth on solid culture medium and the measurement of membrane integrity, membrane potential, esterase and respiratory activities using fluorescent dyes. All measured parameters were responsive to desiccation stress. Results suggested that extending plate count analysis with cultivation-independent methods can greatly enhance resolution especially for moderate stress conditions, which do not get reflected in plate counts due to cellular recovery. Whereas plate counts reflect the final effect on viability, immediate measurement of cellular functions provides a snapshot picture of the fitness status at a specific point in time. Special emphasis was given to MgCl2 which in concentrations≥50mM dramatically increased the bacterial susceptibility to desiccation in the case of the gram-negative bacteria and to a lesser extent also for the gram-positive bacteria. The study in addition confirmed a good agreement of results obtained with the recently developed real-time viability (RTV) assay and the BacLight LIVE/DEAD method in combination with a fluorescence plate reader. ► Bacteria are subjected to drying in the presence or absence of supplements. ► Viability and fitness are assessed using a multiparameter viability assay. ► Presence of magnesium chloride during desiccation greatly reduces viability. ► Presence of extracellular polysaccharides during desiccation increases viability. ► Fluorescent assays offer greater resolution than plate counting for moderate stress.