Weather-related changes in the dehydration of respiratory droplets on surfaces bolster bacterial endurance

Abstract

HypothesisThe study shows for the first time a fivefold difference in the survivability of the bacteriumPseudomonas Aeruginosa(PA) in a realistic respiratory fluid droplet on fomites undergoing drying at different environmental conditions. For instance, in 2023, the annual average relative humidity (RH) in London (UK) is 71%, whereas in Delhi (India), it is 45%, showing that disease spread from fomites could have a demographic dependence. Respiratory fluid droplet ejections containing pathogens on inanimate surfaces are crucial in disease spread, especially in nosocomial settings. However, the interplay between evaporation dynamics, internal fluid flow and precipitation and their collective influence on the distribution and survivability of pathogens at different environmental conditions are less known.ExperimentsShadowgraphy imaging is employed to study evaporation, and optical microscopy imaging is used for precipitation dynamics. Micro-particle image velocimetry (MicroPIV) measurements reveal the internal flow dynamics. Confocal imaging of fluorescently labelled PA elucidates the bacterial distribution within the deposits.FindingsThe study finds that the evaporation rate is drastically impeded during drying at elevated solutal concentrations, particularly at high RH conditions. MicroPIV shows reduced internal flow under high RH conditions. Evaporation rate influences crystal growth, with delayed efflorescence and extending crystallisation times. PA forms denser peripheral arrangements under high evaporation rates and shows a fivefold increase in survivability under low evaporation rates. These findings highlight the critical impact of environmental conditions on pathogen persistence and disease spread from inanimate surfaces.Graphical abstract

Interfacial Stresses within Droplets and Channels Influence Bacterial Physiology: A Perspective

“…Moreover, they substantiated their findings through in vivo experiments, demonstrating that deposition on surfaces, such as door handles as well as tomato and cucumber skins, did not diminish the virulence of the pathogen. The literature has highlighted the mystery surrounding the translation mechanism of shear stresses into biological responses by bacteria. , Rasheed et al investigated the effect of relative humidity (RH) on the evaporation characteristics of a bacteria (Pseudomonas aeruginosa)-laden SRF sessile droplet. They observed a lower evaporation rate in the case of high RH and vice versa, which was supported by lower internal flow inside droplets at high RH conditions.…”

Unravelling the Dynamics of Bacterial-Laden Respiratory Droplets: Epidemiological Transfer from Fomites to Susceptible Host

“…Viable pathogens are found on inanimate surface deposits [5][6][7], that can transfer pathogens through contact. The evaporation and deposition process of respiratory fluid droplets, which contain a complex mix of proteins, electrolytes, and colloids, differs from that of pure solvents [8][9][10]. Factors such as droplet composition [11], drying conditions [12,13], and substrate properties [14] influence evaporation characteristics.…”

“…Pathogen viability on inanimate surfaces can be influenced by environmental conditions and drying-induced stress [9,10,19]. Studies on respiratory droplets have examined deposit morphology, pathogen distribution, and infectivity, but have typically used a single composition of respiratory fluid [8,[20][21][22].…”

“…The evaporation and deposition behaviour of biofluid droplets containing pathogens are critical for understanding disease transfer through fomites. Pathogen viability on inanimate surfaces can be influenced by environmental conditions and drying-induced stress[9,10,19]. Studies on respiratory droplets have examined deposit morphology, pathogen distribution, and infectivity, but have typically used a single composition of respiratory fluid[8,20–22].…”