Physiological Characteristics of Bacterial Droplets Indicate a Catastrophic Consequence With an Increase in Impact Velocity

Abstract

Droplet impacts on various surfaces play a profound role in different bio-physiological processes and engineering applications. The current study opens a new realm that investigates the plausible effect of impact velocities on bacteria-laden droplets against a solid surface. We unveiled the alarming consequences of Salmonella Typhimurium (STM) laden drop, carrying out the in vitro and intracellular viability of STM to the impact Weber numbers ranging from 100-750. The specified Weber number range mimics the velocity range occurring during the respiratory processes, especially the airborne dispersion of drops during cough. A thick ring of bacterial deposition was observed in all cases irrespective of impacting velocity and the nutrient content of the bacterial medium. The mechanical properties of the bacterial deposit examined using Atomic Force Microscopy reveals the deformation of bacterial morphology, cushioning effect and adhesion energy to determine the cell-cell interactions. The impact velocity induces the shear stress onto the cell walls of STM, thereby deteriorating the in vitro viability. However, we found that even with compromised in vitro viability, Salmonella retrieved from deposited patterns impacted at higher velocity revealed an increased expression of phoP (the response regulator of the PhopQ two-component system) and uninterrupted intracellular proliferation in macrophages. The inability of STM ΔphoP growth in nutrient-rich dried droplets to the subjected impact velocities signifies the predominant role of phoP in maintaining the virulence of Salmonella during desiccation stress. Our findings open a promising avenue for understating the effect of bacteria-laden drop impact and its role in disease spread.Abstract Figure

KlebsiellaPneumoniae turns more virulent under flow stresses in capillary like microchannels

“…This difference is significant in straight channel compared to serpentine channels. Similar trends have been previously reported by our group for Salmonella Typhimurium subjected to mechanical stresses 68 . Ares et al 78 reported the importance of cholesterol in reducing the anti-phagocytic properties of KP capsules.…”

Observations on phenomenological changes in Klebsiella Pneumoniae under fluidic stresses

“…67 Interestingly, there can be bacteria that are alive but not culturable. 68 It has been shown that various stress conditions like osmotic stress, 69 thermal stress, 69 oxidative stress, 70 shear stress, 71 evaporative and impact stress 72 result in a loss of viability of the bacterial population. We conduct different tests by maintaining the flow rate and geometry constant in each one of them to understand how the viability of bacterial cells changes.…”

Bacteria–surface interactions: role of impacting bacteria-laden droplets

“…Upon impact, the kinetic energy can create substantial mechanical stresses inside the microbial droplet as it spreads. 28 However, the time scale of the mechanical stresses developed inside the microbial droplet is typically in the range of milliseconds. Our study, however, reveals that this millisecond time scale plays a central role in determining the outcome of the bacterial-surface interactions.…”