Biology subjects

Chakravortty, D.

Publications and source records attributed to Chakravortty, D..

At least 37 records · Page 2Linked to original sources

bioRxiv2024

Evaporation of bacteria-laden surrogate respiratory fluid droplets: On a hydrophilic substrate versus contact-free environment confers differential bacterial infectivity

The transmission of viruses/ bacteria cause infection predominantly via aerosols. The transmission mechanism of respiratory diseases is complex, including direct or indirect contact, large droplet, and airborne routes apart from close contact transmission. With this pretext, we have investigated two modes of droplet evaporation to understand its significance in airborne disease transmission; a droplet in a contact-free environment, which evaporates and forms droplet nuclei, and a droplet on a hydrophilic substrate (fomite). The study examines mass transport, the deposition pattern of bacteria in the precipitates, and their survival and virulence. The osmotic pressure increases with the salt concentration, inactivating the bacteria embedded in the precipitates with accelerated evaporation. Further, the bacterias degree of survival and enhanced pathogenicity are compared for both evaporation modes. The striking differences in pathogenicity are attributed to the evaporation rate, oxygen availability, and reactive oxygen species (ROS) generation.

microbiology↗

bioRxiv2023

Clustered Regularly Interspaced Short Palindromic Repeats-Cas system regulates Salmonella virulence

ObjectivesInvestigating the type 1-E CRISPR-Cas-mediated regulation of Salmonella pathogenesis. MethodsWe assessed the pathogenicity of the wild-type and CRISPR-Cas knockout strains using infection models. The mechanisms were elucidated using antimicrobial assays and expression analysis. ResultsCRISPR-Cas knockout strains were defective in invasion and proliferation in intestinal epithelial cells and macrophages. However, proliferation defects were not observed in the Gp91phox-/- macrophages, suggesting the systems role in antioxidant defence. The knockout strains show hampered colonization in in-vivo infection models, possibly due to increased sensitivity against innate immune barriers like antimicrobial peptides, complement proteins and oxidative stress. The expression studies of various virulence regulators: pmr genes, anti-oxidant genes, SPI-1 and SPI-2 encoded master regulators, and effectors showed repressed expression in the knockout strains. Some of these genes could be directly regulated by the CRISPR-spacers owing to partial complementarity between the sequences. ConclusionOverall, our study shows that the CRISPR-Cas system positively regulates Salmonella pathogenesis by regulating the expression of different virulence factors.

microbiology↗

bioRxiv2023

Salmonella Typhimurium employ spermidine to exert protection against ROS-mediated cytotoxicity and rewires host polyamine metabolism to ameliorate its survival in macrophages

Salmonella infection involves a cascade of attacks and defence measures. After breaching the intestinal epithelial barrier, Salmonella is phagocytosed by the macrophages, inside which, the bacteria face multiple stresses and, consequently, employ appropriate countermeasures. We show that, in Salmonella, the polyamine spermidine activates a stress response mechanism by regulating critical antioxidant genes. Salmonella Typhimurium mutants for spermidine transport and synthesis cannot mount an antioxidative response, resulting in high intracellular ROS levels. These mutants are also compromised in their ability to be phagocytosed by macrophages. Furthermore, it regulates a novel enzyme in Salmonella, Glutathionyl-spermidine synthetase (GspSA), which is known to prevent the oxidation of proteins in E.coli. Moreover, the spermidine mutants and the GspSA mutant show significantly reduced survival in the presence of hydrogen peroxide in vitro, and lesser organ burden in the mouse model of Salmonella infection. Conversely, in macrophages isolated from gp91phox-/- mice, we observed a rescue in the attenuated fold proliferation previously observed upon infection. Interestingly, Salmonella upregulates polyamine biosynthesis in the host through its effectors from SPI-1 and SPI-2, which also solves the mystery of the attenuated proliferation observed in spermidine transport mutants. Thus, inhibition of this pathway in the host abrogates the proliferation of Salmonella Typhimurium in macrophages. From a therapeutic perspective, inhibiting host polyamine biosynthesis using an FDA-approved chemopreventive drug, D,L--difluoromethylornithine (DFMO), reduces Salmonella colonization and tissue damage in the mouse model of infection, while enhancing the survival of infected mice. Therefore, our work provides a mechanistic insight into the critical role of spermidine in stress resistance of Salmonella. It also reveals a strategy of the bacteria in modulating host metabolism to promote their intracellular survival and shows the potential of DFMO to curb Salmonella infection.

microbiology↗

bioRxiv2023

Klebsiella Pneumoniae turns more virulent under flow stresses in capillary like microchannels

Fluidic habitats are very common to bacterial life, however, very little is known about the effect of the flow stresses on the virulence of the bacteria. In the present work, we conduct microfluidic experiments to understand the consequence of stresses generated by flowing fluid on the bacterial morphology and virulence. We consider Klebsiella pneumoniae (KP), an ESKAPE pathogen as the model bacteria that are responsible for blood stream infections like bacteremia apart from pneumonia, urinary tract infections and more. We generate four different stress conditions by changing the flow rate and channel geometry subsequently altering the shear rate and stressing time ({tau}). We observe significant changes in the structural aspects of the stressed bacteria. With an increase in stressing parameters, the viability of the bacterial sample deteriorated. Most importantly, these stressed samples proliferate much more than unstressed samples inside the RAW264.7 murine macrophages. The results shed light on the complex relationship between flow stresses and bacterial virulence. Furthermore, we challenge the bacterial samples with ciprofloxacin to see how they behave under different stress conditions. The present study can be extended to model deadly diseases like bacteremia using organ-on-a-chip technology and help understand bacterial pathogenicity under realistic environments. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/558194v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1111ea1org.highwire.dtl.DTLVardef@f20494org.highwire.dtl.DTLVardef@10ac86dorg.highwire.dtl.DTLVardef@ec6eb1_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure:C_FLOATNO A schematic representation of the present work. Figure created with BioRender (www.biorender.com) C_FIG

biophysics↗

bioRxiv2023

SIRT1 and SIRT3 impact host mitochondrial function and host- Salmonella pH balance during infection

Mitochondria are an important organelle regulating energy homeostasis. Mitochondrial health and dynamics are crucial determinants of the outcome of several bacterial infections. SIRT3, a major mitochondrial sirtuin, along with SIRT1 regulates key mitochondrial functions. This led to considerable interest in understanding the role of SIRT1 and SIRT3 in governing mitochondrial functions during Salmonella infection. Here, we show that loss of SIRT1 and SIRT3 function either by shRNA-mediated knockdown or inhibitor treatment led to increased mitochondrial dysfunction with alteration in mitochondrial bioenergetics alongside increased mitochondrial superoxide generation in the Salmonella-infected macrophages. Consistent with dysfunctional mitochondria, mitophagy was induced along with altered mitochondrial fusion-fission dynamics in S. Typhimurium-infected macrophages. Additionally, the mitochondrial bioenergetic alteration promotes acidification of the infected macrophage cytosolic pH. This host cytosolic pH imbalance skewed the intra-phagosomal and intra- bacterial pH in the absence of SIRT1 and SIRT3, resulting in decreased SPI-2 gene expression. Our results suggest a novel role of SIRT1 and SIRT3 in maintaining the intracellular Salmonella niche by modulating the mitochondrial bioenergetics and dynamics in the infected macrophages. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/557159v2_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@486cbaorg.highwire.dtl.DTLVardef@da2fb0org.highwire.dtl.DTLVardef@70cd46org.highwire.dtl.DTLVardef@1b4d0bd_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

A host AAA-ATPase exhibits bacteriolytic activity for clearance of microbial infection

An array of host cytosol guarding factors impede bacterial proliferation and preserve cellular sterility. Amongst them, proteasomal degradation of ubiquitinated pathogens has emerged as a critical mechanism for ensuring cytosolic sanctity. We wondered how proteasomes, with their small size and inability to extract membrane-bound proteins, can eradicate pathogens. Here, we unveil a unique strategy, wherein VCP/p97, a host AAA-ATPase, eliminates pathogens by exerting mechanical force that physically unfolds and pulls out ubiquitinated proteins from bacterial membrane. Combining a single-molecule approach along with molecular dynamic simulation and in-vitro reconstitution, we demonstrate that protein extraction by p97 causes extensive membrane lysis and release of cytosolic contents from phylogenetically diverse microbes. Additionally, in an in-vivo mouse sepsis model, this segregase-dependent bactericidal effect of p97 abrogated microbial proliferation in host tissues. Overall, we discovered a distinct innate antimicrobial function of p97, that protects the host against lethal bacterial infections. One Sentence SummaryA host AAA-ATPase exhibits bacteriolytic activity.

microbiology↗

bioRxiv2023

Spermidine facilitates the adhesion and subsequent invasion of Salmonella Typhimurium into epithelial cells via the regulation of surface adhesive structures and the SPI-1

Polyamines are poly-cationic molecules ubiquitously present in all organisms. Salmonella synthesizes and also harbors specialized ABC transporters to uptake polyamines. Polyamines assist in pathogenesis and stress resistance in Salmonella; however, the mechanism remains elusive. The virulence trait of Salmonella depends on the injection of effector proteins into the host cell and modulation of host machinery and employs an array of arsenals to colonize in the host niche successfully. However, prior to this, Salmonella utilizes multiple surface structures to attach and adhere to the surface of the target cells. Our study solves the enigma of how polyamine spermidine assists in the pathogenesis of Salmonella. We show that spermidine mediates the initial attachment and adhesion of Salmonella Typhimurium to Caco-2 cells, facilitating its invasion. In-vivo studies showed that polyamines are required for invasion into the murine Peyers patches. Polyamines have previously been shown to regulate the transcription of multiple genes in both eukaryotes and prokaryotes. We show that spermidine controls the RNA expression of the two-component system, BarA/SirA, that further regulates multiple fimbrial and non-fimbrial adhesins in Salmonella. Flagella is also a vital surface structure aiding in motility and attachment to surfaces of host cells and gall stones. Spermidine regulated the expression of flagellin genes by enhancing the translation of s28, which features an unusual start codon and a poor Shine-Dalgarno sequence. Besides regulating the formation of the adhesive structures, spermidine tunes the expression of the Salmonella pathogenicity island-1 encoded genes. Thus, our study unravels a novel mechanism by which spermidine aids in the adhesion and the subsequent invasion of Salmonella into host cells.

microbiology↗

bioRxiv2023

Salmonella Typhimurium effector SseI regulates host peroxisomal dynamics to acquire lysosomal cholesterol for better intracellular growth

Intracellular Salmonella resides and multiplies in cholesterol-rich specialized compartment called Salmonella-containing vacuoles (SCVs) and avoids fusion with acidic lysosomes. Given, lysosomes are primary organelle that redistributes LDL derived cholesterol to other organelles; we questioned how lysosomal cholesterol can be transported to SCV. We demonstrate here that peroxisomes are recruited to SCVs in human primary macrophages, epithelial cells and functions as pro-bacterial organelles. Further, this interaction is assisted by SseI, a Salmonella effector protein containing mammalian peroxisome targeting sequence. SseI localizes to peroxisome, interacts and activates a host Ras GTPase, ARF-1 on the peroxisome membrane. Activation of ARF-1 leads to recruitment of phosphatidylinsolitol-5- phosphate-4 kinase to generate phosphatidylinsolitol-4-5-bisphosphate on peroxisomes. Accordingly, the{Delta} sseI strain showed reduced virulence in cell lines and during mice infection. Taken together, our work identified a fascinating mechanism by which a pathogen targets host organelles via its secretory effectors and exploits host metabolic intermediates for its intracellular proliferation.

cell biology↗

bioRxiv2022

SIRT1 and SIRT3 mediated immuno-metabolic switch govern Salmonella survival within infected macrophages both in vitro and in vivo.

Sirtuins are the major players in host immuno-metabolic regulation. However, the role of sirtuins in the modulation of the immune metabolism pertaining to Salmonellosis is largely unknown. Here, our investigation focussed on the role of two important sirtuins, SIRT1 and SIRT3, shedding light on their impact on intracellular Salmonellas metabolic switch and pathogenesis establishment. Our study indicated the ability of the live Salmonella Typhimurium to differentially regulate the levels of SIRT1 and SIRT3 for maintaining the high glycolytic metabolism and low fatty acid metabolism in Salmonella. Perturbing SIRT1 or SIRT3 through knockdown or inhibition, resulted in a remarkable shift in the host metabolism to low fatty acid oxidation and high glycolysis. This switch led to decreased proliferation of Salmonella in the macrophages. Further, Salmonella-induced higher levels of SIRT1 and SIRT3 led to a skewed polarization state of the macrophages from a pro-inflammatory M1 state toward an immunosuppressive M2 making it more conducive for the intracellular life of Salmonella. Alongside, governing immunological functions by modulating p65 NF-{kappa}B acetylation, SIRT1, and SIRT3 also skew Salmonella-induced host metabolic switch by regulating the acetylation status of HIF-1 and PDHA1. Interestingly, though knock-down of SIRT1/3 attenuated Salmonella proliferation in macrophages, in in vivo mice-model of infection, inhibition or knockdown of SIRT1/3 led to more dissemination and higher organ burden which can be attributed to enhanced ROS and IL-6 production. Our study hence reports for the first time that Salmonella modulates SIRT1/3 levels to maintain its own metabolism for successful pathogenesis.

microbiology↗

bioRxiv2022

Syntaxin 3-SPI 2 dependent cross-talk facilitates the division of Salmonella containing vacuole (SCV)

Intracellular membrane fusion is mediated by membrane-bridging complexes of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SNARE proteins are one of the key players in the vesicular transport. Several reports shed light on intracellular bacteria modulating host SNARE machinery to establish infection successfully. The critical SNAREs in macrophages responsible for phagosome maturation are Syntaxin 3 (STX3) and Syntaxin 4 (STX4). Salmonella actively modulates its vacuole membrane composition to escape lysosomal fusion. A report showed that Salmonella containing vacuole (SCV) harbors recycling endosomal SNARE Syntaxin 12 (STX12). However, the role of host SNAREs in SCV biogenesis and pathogenesis is unclear. Upon knockdown of STX3, we have observed a reduction in bacterial proliferation and is restored upon the overexpression of STX3. Post infected live-cell imaging of cells showed STX3 localises to the SCV membranes and thus might help in fusion of SCV with intracellular vesicles to acquire membrane for its division. We also found this interaction abrogated when we infected with SPI-2 encoded T3SS apparatus mutant (STM {Delta}ssaV) but not with SPI-1 encoded T3SS (STM{Delta} invC). These observations were also consistent in mice model of Salmonella infection. Together, these results shed a light on the effector molecules secreted through SPI-2 encoded by T3SS possibly involved in interaction with host SNARE STX3, which is essential to maintain the division of Salmonella in SCV and maintenance the principle single bacterium per vacuole. SynopsisSalmonella Typhimurium infection in murine macrophage leads to upregulation of host Syntaxin 3 both at transcript and protein levels at late stage of infection. Syntaxin 3 cross-talk with Salmonella containing vacuoles (SCVs) is essential for establishment of replicative niche in host macrophages. The cross-talk between STX3 and SCVs is Salmonella pathogenicity island 2 (SPI-2) dependent and is consistent in mice model of Salmonella Typhimurium infection.

microbiology↗

bioRxiv2022

PHYSIOLOGICAL CHARACTERISTICS OF BACTERIAL DROPLETS INDICATE A CATASTROPHIC CONSEQUENCE WITH AN INCREASE IN IMPACT VELOCITY

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{Delta} phoP 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. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

bioengineering↗

bioRxiv2022

Physics of Self-Assembly and Morpho-Topological Changes of Klebsiella Pneumoniae in Desiccating Sessile Droplets

We have investigated the flow and desiccation-driven self-assembly of Klebsiella Pneumoniae in the naturally evaporating sessile droplets. Klebsiella Pneumoniae exhibits extensive changes in its morphology and forms unique patterns as the droplet dries, revealing hitherto unexplored rich physics governing its survival and infection strategies. Self-assembly of bacteria at the droplet contact line is characterized by order-to-disorder packing transitions with high packing densities and excessive deformations (bacteria deforms nearly twice its original length scales). In contrast, thin-film instability-led hole formation at the center of the droplet engenders spatial packing of bacteria analogous to honeycomb weathering. The varying physical forces acting on bacteria based on their respective spatial location inside the droplet cause an assorted magnitude of physical stress. Self-assembly favors the bacteria at the rim of the droplet, leading to enhanced viability and pathogenesis on the famously known "coffee ring" of the droplet compared to the bacteria present at the center of the droplet residue. Mechanistic insights gained via our study can have far-reaching implications for bacterial infection through droplets, e.g., through open wounds.

microbiology↗

bioRxiv2022

Deceiving The Big Eaters: Salmonella Typhimurium SopB subverts host cell Xenophagy through the Akt-TFEB axis in macrophages

Salmonella, a stealthy facultative intracellular pathogen, harbors an array of host immune evasion strategies. This facilitates successful survival and replicative niches establishment in otherwise hostile host innate immune cells such as macrophages. Salmonella survives and utilizes macrophages for effective dissemination throughout the host causing systemic infection. One of the central host defense mechanisms in macrophages is bacterial xenophagy or macro-autophagy. Here we report for the first time that Salmonella pathogenicity island-1 (SPI-1) effector SopB is involved in subverting host autophagy through dual mechanisms. SopB is known to act as a phosphoinositide phosphatase and thereby can alter the phosphoinositide dynamics of the host cell. Here we demonstrate that this activity helps the bacterium escape autophagy by inhibiting terminal fusion of Salmonella containing vacuole (SCV) with both lysosomes and autophagosomes. We also report the second mechanism, wherein SopB downregulates overall lysosomal biogenesis through Akt- transcription factor EB (TFEB) axis. TFEB is a master regulator of lysosomal biogenesis and autophagy, and SopB restricts the nuclear localization of TFEB. This reduces the overall lysosome content inside host macrophages, further facilitating survival in macrophages and systemic dissemination of Salmonella in the host.

microbiology↗

bioRxiv2022

Outer membrane protein A (OmpA) deficient Salmonella Typhimurium displays enhanced susceptibility towards β-lactam antibiotics: third-generation cephalosporins (ceftazidime) and carbapenems (meropenem)

The invasive non-typhoidal serovar of Salmonella enterica, namely Salmonella Typhimurium ST313, causes bloodstream infection in sub-Saharan Africa. Like other bacterial pathogens, the development of antimicrobial resistance is a severe problem in curing non-typhoidal Salmonella infection. In this work, we have investigated the role of four prominent outer membrane porins of S. Typhimurium, namely OmpA, OmpC, OmpD, and OmpF, in resistance against broad-spectrum {beta}-lactam antibiotics-ceftazidime and meropenem. We found that deleting OmpA from Salmonella makes the bacteria susceptible to {beta}-lactam drugs. The MIC for both the antibiotics reduced significantly for STM{Delta} ompA compared to the wild-type and the ompA complemented strains. Despite the presence of antibiotics, the uninterrupted growth of STM{Delta} ompC,{Delta} ompD, and{Delta} ompF endorsed the dispensability of these three porins in antimicrobial resistance. The {beta}-lactam antibiotics caused massive depolarization in the outer membrane of the bacteria in the absence of OmpA. We have proved that none of the extracellular loops but the complete structure of perfectly folded OmpA is required by the bacteria for developing antimicrobial resistance. Our data revealed that STM{Delta} ompA consumed more antibiotics than the wild-type and the complemented strain, resulting in severe damage of the bacterial outer membrane and subsequent killing of the pathogen by antibiotic-mediated oxidative stress. Upon deleting ompA, the steady decrease in the relative proportion of antibiotic-resistant persisters and the clearance of the STM{Delta} ompA from the liver and spleen of C57BL/6 mice upon treatment with ceftazidime proved the role of OmpA in rendering protection against {beta}-lactam antibiotics.

microbiology↗

bioRxiv2021

The extracellular loops of Salmonella Typhimurium outer membrane protein A (OmpA) maintain the stability of Salmonella containing vacuole (SCV) in murine macrophages and protect the bacteria from autophagy-dependent lysosomal degradation

After entering the host cells, Salmonella Typhimurium (STM) stays inside a modified membrane-bound compartment called Salmonella containing vacuole (SCV). The biogenesis and stability of SCV are crucial for the intracellular proliferation of Salmonella. Our research has provided a novel mechanistic view on the role of a bacterial porin OmpA in maintaining the stability of SCV. We found that the deletion of OmpA forces the bacteria to escape from the SCV during the immediate early stage of infection. In the absence of OmpA, the bacteria failed to retain the LAMP-1 and came into the host cells cytosol. Subsequently, the cytosolic population of STM{Delta} ompA activated the host autophagy machinery after colocalizing with syntaxin 17 and LC3B. The autophagosomes carrying STM{Delta} ompA were targeted to the lysosomes for degradation. Inhibition of autophagy pathway using bafilomycin A1 restored the intracellular proliferation of STM{Delta} ompA. We further showed that the four extracellular loops of OmpA played a crucial role in holding the LAMP-1 pool around the SCV. We have altered the extracellular loop sequences of Salmonella OmpA by site-directed mutagenesis and observed that the bacteria failed to maintain the LAMP-1 pool around the SCV, which finally resulted in their release into the cytosol of the host macrophages. Surprisingly, the cytosolic population of Salmonella having mutations in the extracellular loops of OmpA didnt activate the lysosomal degradation pathway like STM{Delta} ompA, which helped them to survive within the murine macrophages. In summary, our study revealed an OmpA dependent novel strategy utilized by Salmonella to combat host autophagy by promoting the stability of SCV.

microbiology↗

bioRxiv2021

A novel innate pathogen sensing strategy involving ubiquitination of bacterial surface proteins

Sensing of pathogens by ubiquitination is critical for maintaining cytosolic sanctity. However, universal ubiquitination targets on bacteria, especially of proteinaceous origin, remain unidentified. Here, we unveil a novel strategy, involving recognition of degron-like motifs for identification of first protein-based ubiquitination substrates on phylogenetically distinct bacteria. Such motifs can form a new class of intra-cytosolic pathogen associated molecular patterns (PAMPs) as their incorporation enables identification of non-ubiquitin targets by host Ub-ligases. We find SCFFBW7 E3-ligase, supported by the regulatory kinase, GSK3{beta}, is crucial for effective pathogen detection and clearance. This may explain the enhanced risk of infections in Chronic Lymphocytic Leukaemia patients bearing FBXW7 mutations. We conclude that exploitation of such ubiquitous pathogen sensing strategy allows conservation of cellular resources and boost anti-microbial immunity. One Sentence SummaryUbiquitination of bacterial surface proteins fosters sensing and clearance of diverse pathogens

microbiology↗

bioRxiv2021

GH18 family glycoside hydrolase Chitinase A of Salmonella facilitates bacterial invasion and survival by modulating host immune responses

Salmonella is a facultative intracellular pathogen that has co-evolved with its host and has also developed various strategies to evade the host immune responses. Salmonella recruits an array of virulence factors to escape from host defense mechanisms. Previously chitinase A (chiA) was found to be upregulated in intracellular Salmonella. Although studies show that chitinases and chitin binding proteins (CBP) of many human pathogens have a profound role in various aspects of pathogenesis, like adhesion, virulence and immune evasion, the role of chitinase in strict intravacuolar pathogen Salmonella has not yet been elucidated. In this study, we deciphered the role of chitinase of Salmonella in the pathogenesis of the serovars, Typhimurium and Typhi. Our data propose that ChiA mediated modification of the glycosylation on the epithelial cell surface facilitates the invasion of the pathogen into the epithelial cells. Further we found that ChiA aids in reactive nitrogen species (RNS) and reactive oxygen species (ROS) production in phagocytes, leading to MHCII downregulation followed by suppression of antigen presentation and antibacterial responses. In continuation of the study in animal model C. elegans, Salmonella Typhi ChiA was found to facilitate attachment to the intestinal epithelium, gut colonization and persistence by downregulating antimicrobial peptides.

microbiology↗

bioRxiv2021

Vapor mediation as a tool to control micro-nano scale dendritic crystallization and preferential bacterial distribution in drying respiratory droplets

Deposits of biofluid droplets on surfaces (such as respiratory droplets formed during an expiratory event fallen on surfaces) are composed of the water-based salt-protein solution that may also contain an infection (bacterial/viral).The final patterns of the deposit formed are dictated by the composition of the fluid and flow dynamics within the droplet. This work reports the spatio-temporal, topological regulation of deposits of respiratory fluid droplets and control of motility of bacteria by tweaking flow inside droplets using non-contact vapor-mediated interactions. When evaporated on a glass surface, respiratory droplets form haphazard multiscale dendritic, cruciform-shaped precipitates--using vapor mediation as a tool to control these deposits at the level of nano-micro-millimeter scales. Wemorphologically control dendrite orientation, size and subsequently suppress cruciform-shaped crystals. The nucleation sites are controlled via preferential transfer of solutes in the droplets; thus, achieving control over crystal occurrence and growth dynamics. The active living matter like bacteria is also preferentially segregated with controlled motility without attenuation of its viability and pathogenesis. For the first time, we have experimentally presented a proof-of-concept to control the motion of live active matter like bacteria in a near non-intrusive manner. The methodology can have ramifications in biomedical applications like disease detection, controlling bacterial motility, and bacterial segregation.

bioengineering↗