Functional analysis of superoxide dismutase ofSalmonellatyphimurium in serum resistance and biofilm formation

Synergistic antimicrobial activity of alpha-linolenic acid in combination with tetracycline or florfenicol against multidrug-resistant Salmonella typhimurium

Salmonella is a major foodborne pathogen that can be transmitted from livestock and poultry to humans through the food chain. Due to the widespread use of antibiotics, antibiotic resistance Salmonella has become an important factor threatening food safety. Combining antibiotic and non-antibiotic agents is a promising approach to address the widespread emergence of antibiotic-resistant pathogens. In this study, we investigated the antibiotic resistance profile and molecular characterization of different serotypes of Salmonella isolated from large-scale egg farms using drug susceptibility testing and whole genome sequencing. The synergistic effect of alpha-linolenic acid (ALA) with antibiotics was evaluated using the checkerboard test and time-kill curve. The molecular mechanism of α-linolenic acid synergism was explored using biochemical assays, pull-down assays, and molecular docking. In vivo efficacy of ALA in combination with florfenicol (FFC) or tetracycline (TET) against multidrug-resistant (MDR) Salmonella enterica subsp. enterica serovar typhimurium was also investigated using a mouse model. We found that ALA reduced the minimum inhibitory concentration (MIC) of tetracycline and florfenicol in all strains tested. When ALA (512 mg/L) was combined with florfenicol (32 mg/L) or tetracycline (16 mg/L), we observed disruption of cell membrane integrity, increased outer membrane permeability, lowered cell membrane potential, and inhibition of proton-drive-dependent efflux pumps. The synergistic treatment also inhibited biofilm production and promoted oxidative damage. These changes together led to an increase in bacterial antibiotic susceptibility. The improved efficacy of ALA combination treatment with antibiotics was validated in the mouse model. Molecular docking results indicate that ALA can bind to membrane proteins via hydrogen bonding. Our findings demonstrated that combined treatment using ALA and antibiotics is effective in preventing infections involving MDR bacteria. Our results are of great significance for the scientific and effective prevention and control of antibiotic resistance Salmonella, as well as ensuring food safety.

Phenotypic impacts and genetic regulation characteristics of the DNA adenine methylase gene (dam) in Salmonella Typhimurium biofilm forms

In this study, transcriptional level gene expression changes in biofilm forms of Salmonella Typhimurium ATCC 14028 and its dam mutant were investigated by performing RNAseq analysis. As a result of these analyzes, a total of 233 differentially expressed genes (DEGs) were identified in the dam mutant, of which 145 genes were downregulated and 88 genes were upregulated compared to the wild type. According to data from miRNA sequence analysis, of 13 miRNAs differentially expressed in dam mutant, 9 miRNAs were downregulated and 4 miRNAs were upregulated. These data provide the first evidence that the dam gene is a global regulator of biofilm formation in Salmonella. In addition, phenotypic analyses revealed that bacterial swimming and swarming motility and cellulose production were highly inhibited in the dam mutant. It was determined that bacterial adhesion in Caco-2 and HEp-2 cell lines was significantly reduced in dam mutant. At the end of 90 min, the adhesion rate of wild type strain was 43.3% in Caco-2 cell line, while this rate was 14.9% in dam mutant. In the HEp-2 cell line, while 45.5% adherence was observed in the wild-type strain, this rate decreased to 15.3% in the dam mutant.

Genome-wide characterization of Salmonella Typhimurium genes required for the fitness under iron restriction

Background

Iron is a crucial element for bacterial survival and virulence. During Salmonella infection, the host utilizes a variety of mechanisms to starve the pathogen from iron. However, Salmonella activates distinctive defense mechanisms to acquire iron and survive in iron-restricted host environments. Yet, the comprehensive set of the conditionally essential genes that underpin Salmonella survival under iron-restricted niches has not been fully explored.

Results

Here, we employed transposon sequencing (Tn-seq) method for high-resolution elucidation of the genes in Salmonella Typhimurium (S. Typhimurium) 14028S strain required for the growth under the in vitro conditions with four different levels of iron restriction achieved by iron chelator 2,2′-dipyridyl (Dip): mild (100 and 150 μM), moderate (250 μM) and severe iron restriction (400 μM). We found that the fitness of the mutants reduced significantly for 28 genes, suggesting the importance of these genes for the growth under iron restriction. These genes include sufABCDSE, iron transport fepD, siderophore tonB, sigma factor E ropE, phosphate transport pstAB, and zinc exporter zntA. The siderophore gene tonB was required in mild and moderate iron-restricted conditions, but it became dispensable in severe iron-restricted conditions. Remarkably, rpoE was required in moderate and severe iron restrictions, leading to complete attenuation of the mutant under these conditions. We also identified 30 genes for which the deletion of the genes resulted in increased fitness under iron-restricted conditions.

Conclusions

The findings broaden our knowledge of how S. Typhimurium survives in iron-deficient environments, which could be utilized for the development of new therapeutic strategies targeting the pathways vital for iron metabolism, trafficking, and scavenging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01069-3.

Environmentally relevant concentrations of microplastics modulated the immune response and swimming activity, and impaired the development of marine medaka Oryzias melastigma larvae

Microplastics (MPs), due to their impacts on the ecosystem and their integration into the food web either through trophic transfer or ingestion directly from the ambient environment, are an emerging class of environmental contaminants posing a great threat to marine organisms. Most reports on the toxic effects of MPs exclusively focus on bioaccumulation, oxidative stress, pathological damage, and metabolic disturbance in fish. However, the collected information on fish immunity in response to MPs is poorly defined. In particular, little is known regarding mucosal immunity and the role of mucins. In this study, marine medaka (Oryzias melastigma) larvae were exposed to 6.0 µm beads of polystyrene microplastics (PS-MPs) at three environmentally relevant concentrations (10² particles/L, 10⁴ particles/L, and 10⁶ particles/L) for 14 days. The experiment was carried out to explore the developmental and behavioural indices, the transcriptional profiles of mucins, pro-inflammatory, immune, metabolism and antioxidant responses related genes, as well as the accumulation of PS-MPs in larvae. The results revealed that PS-MPs were observed in the gastrointestinal tract, with a concentration- and exposure time-dependent manner. No significant difference in the larval mortality was found between the treatment groups and the control, whereas the body length of larvae demonstrated a significant reduction at 10⁶ particles/L on 14 days post-hatching. The swimming behaviour of the larvae became hyperactive under exposure to 10⁴ and 10⁶ particles/L PS-MPs. In addition, PS-MP exposure significantly up-regulated the mucin gene transcriptional levels of muc7-like and muc13-like, however down-regulated the mucin gene expression levels of heg1, muc2, muc5AC-like and muc13. The immune- and inflammation and metabolism-relevant genes (jak, stat-3, il-6, il-1β, tnf-а, ccl-11, nf-κb, and sod) were significantly induced by PS-MPs at 10⁴ and 10⁶ particles/L compared to the control. Taken together, this study suggests that PS-MPs induced inflammation response and might obstruct the immune functions and retarded the growth of the marine medaka larvae even at environmentally relevant concentrations.

GH18 family glycoside hydrolase Chitinase A of Salmonella enhances virulence by facilitating invasion and 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 several structurally similar 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 the intravacuolar pathogen Salmonella has not yet been elucidated. Therefore, we made chromosomal deletions of the chitinase encoding gene (chiA) to study the role of chitinase of Salmonella enterica in the pathogenesis of the serovars, Typhimurium, and Typhi using in vitro cell culture model and two different in vivo hosts. Our data indicate that ChiA removes the terminal sialic acid moiety from the host cell surface, and facilitates the invasion of the pathogen into the epithelial cells. Interestingly we found that the mutant bacteria also quit the Salmonella-containing vacuole and hyper-proliferate in the cytoplasm of the epithelial cells. Further, we found that ChiA aids in reactive nitrogen species (RNS) and reactive oxygen species (ROS) production in the phagocytes, leading to MHCII downregulation followed by suppression of antigen presentation and antibacterial responses. Notably, in the murine host, the mutant shows compromised virulence, leading to immune activation and pathogen clearance. In continuation of the study in C. elegans, Salmonella Typhi ChiA was found to facilitate bacterial attachment to the intestinal epithelium, intestinal colonization, and persistence by downregulating antimicrobial peptides. This study provides new insights on chitinase as an important and novel virulence determinant that helps in immune evasion and increased pathogenesis of Salmonella.

Quantitative proteomic analysis of marine biofilms formed by filamentous cyanobacterium

Cyanobacterial molecular biology can identify pathways that affect the adhesion and settlement of biofouling organisms and, consequently, obtain novel antifouling strategies for marine applications. Proteomic analyses can provide an essential understanding of how cyanobacteria adapt to different environmental settings. However, only a few qualitative studies have been performed in some cyanobacterial strains. Considering the limited knowledge about protein expression in cyanobacteria in different growing conditions, a quantitative proteomic analysis by LC-MS/MS of biofilm cells from a filamentous strain was performed. Biofilms were also analysed through standard methodologies for following cyanobacterial biofilm development. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4 s^-1 and 40 s^-1). Biofilm development was higher at 4 s^-1 and no significant differences were found between surfaces. Proteomic analysis identified 546 proteins and 41 were differentially expressed. Differences in protein expression were more noticeable between biofilms formed on glass and perspex at 4 s^-1. When comparing biofilms formed on different surfaces, results suggest that biofilm development may be related to the expression of several proteins like a beta-propeller domain-containing protein, chaperone DnaK, SLH domain-containing proteins, an OMF family outer membrane protein, and/or additional uncharacterized proteins. Regarding the hydrodynamic effect, biofilm development can be related to SOD enzyme expression, to proteins related to photosynthetic processes and to a set of uncharacterized proteins with calcium binding domains, disordered proteins, and others involved in electron transfer activity. Studies that combine distinct approaches are essential for finding new targets for antibiofilm agents. The characterisation performed in this work provides new insights into how shear rate and surface affect cyanobacterial biofilm development and how cyanobacteria adapt to these different environmental settings from a macroscopic standpoint to a proteomics context.

Cappable-Seq Reveals Specific Patterns of Metabolism and Virulence for Salmonella Typhimurium Intracellular Survival within Acanthamoeba castellanii

The bacterial pathogen Salmonella enterica, which causes enteritis, has a broad host range and extensive environmental longevity. In water and soil, Salmonella interacts with protozoa and multiplies inside their phagosomes. Although this relationship resembles that between Salmonella and mammalian phagocytes, the interaction mechanisms and bacterial genes involved are unclear. Here, we characterized global gene expression patterns of S. enterica serovar Typhimurium within Acanthamoeba castellanii at the early stage of infection by Cappable-Seq. Gene expression features of S. Typhimurium within A. castellanii were presented with downregulation of glycolysis-related, and upregulation of glyoxylate cycle-related genes. Expression of Salmonella Pathogenicity Island-1 (SPI-1), chemotaxis system, and flagellar apparatus genes was upregulated. Furthermore, expression of genes mediating oxidative stress response and iron uptake was upregulated within A. castellanii as well as within mammalian phagocytes. Hence, global S. Typhimurium gene expression patterns within A. castellanii help better understand the molecular mechanisms of Salmonella adaptation to an amoeba cell and intracellular persistence in protozoa inhabiting water and soil ecosystems.

Biochemical and molecular changes of the zosteric acid-treated Escherichia coli biofilm on a mineral surface

Purpose

The main goal of the present work was to assess the effectiveness of zosteric acid (ZA) in hindering Escherichia coli biofilm formation on a mineral surface.

Methods

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) flow system was used to probe in situ the biochemical changes induced by ZA on E. coli sessile cells growing on the zinc selenide ATR plate. Comparative proteome analysis was conducted on the sessile cells to better understand the principal molecular changes that occur on ZA-treated biofilms.

Results

The ZA treatment modified the kinetics of the biofilm development. After the ZA exposure, dramatic changes in the carbohydrates, proteins, and DNA profiles were observed over time in the ATR-FTIR spectra. These results were translated into the physiological effects such as the reduction of both the biomass and the EPS contents, the inhibition of the biofilm growth, and the promotion of the detachment. In E. coli sessile cells, the comparative proteome analysis revealed that, while the stress responses were upregulated, the pathways belonging to the DNA replication and repair were downregulated in the ZA-treated biofilms.

Conclusions

The ZA reduced the binding capability of E. coli cells onto the ZnSe crystal, hindering the firm adhesion and the subsequent biofilm development on a mineral surface. The variation of the protein patterns indicated that the ZA acted as a stress factor on the sessile cells that seemed to discourage biomass proliferation, consequently decreasing the surface colonization.

Relation of the pdxB-usg-truA-dedA Operon and the truA Gene to the Intracellular Survival of Salmonella enterica Serovar Typhimurium

Salmonella is the genus of Gram-negative, facultative intracellular pathogens that have the ability to infect large numbers of animal or human hosts. The S. enterica usg gene is associated with intracellular survival based on ortholog screening and identification. In this study, the λ-Red recombination system was used to construct gene deletion strains and to investigate whether the identified operon was related to intracellular survival. The pdxB-usg-truA-dedA operon enhanced the intracellular survival of S. enterica by resisting the oxidative environment and the usg and truA gene expression was induced by H₂O₂. Moreover, the genes in this operon (except for dedA) contributed to virulence in mice. These findings indicate that the pdxB-usg-truA-dedA operon functions in resistance to oxidative environments during intracellular survival and is required for in vivo S. enterica virulence. This study provides insight toward a better understand of the characteristics of intracellular pathogens and explores the gene modules involved in their intracellular survival.