Small non-coding RNA STnc640 regulates expression of fimA fimbrial gene and virulence of Salmonella enterica serovar Enteritidis

STnc1280, a trans-coding sRNA is involved in virulence modulation via targeting gldA mRNA in Salmonella Typhimurium

Introduction. Salmonella Typhimurium (STM) is a food-borne Gram-negative bacterium, which can infect humans and a wide range of livestock and poultry, causing a variety of diseases such as septicaemia, enteritis and abortion.Hypothesis/Gap Statement. We will decipher the impacts of sRNA STnc1280 on STM virulence and provide a theoretical basis to reveal the regulatory role and molecular mechanism of STnc1280.Aim. The main objective of this study was to clarify whether sRNA STnc1280 exerts regulatory roles on STM pathogenicity.Methodology. The STnc1280 gene was amplified and its molecular characteristics were analysed in this study. Then, STnc1280 gene deletion strain (STM-ΔSTnc1280) and the complementary strain (ΔSTnc1280/STnc1280) were constructed by λ-Red homologous recombination method, respectively, to analyse of adhesion and invasive ability and pathogenicity of different strains. Subsequently, the potential target gene regulated by STnc1280 was predicted using target RNA2 software, followed by the verification of the interaction between STnc1280 and target mRNA using the dual plasmid reporter system (DPRS). Furthermore, the mRNA and protein level of target gene was determined using qRT-PCR and Western blot, respectively.Results. The results revealed that the cell adhesion and invasive ability and pathogenicity of STM-ΔSTnc1280 were significantly reduced compared to STM-SL1344 strain, indicating that the deficiency of STnc1280 gene significantly influenced STM pathogenicity. The DPRS results showed that STnc1280 can interact with the mRNA of target gene gldA, thus suppressing the expression of lacZ gene. Furthermore, the level of gldA mRNA was not influenced in STM-ΔSTnc1280, but the expression of GldA protein decreased significantly.Conclusion. Combining the bioinformatic analysis, these findings suggested that STnc1280 may bind to the SD sequence of gldA mRNA, hindering the binding of ribosomes to gldA mRNA, thereby inhibiting the expression of GldA protein to modulate the virulence of STM.

Virulence genes identification in Salmonella enterica isolates from humans, crocodiles, and poultry farms from two regions in Colombia

Background and Aim

Salmonella spp. is frequently found in the digestive tract of birds and reptiles and transmitted to humans through food. Salmonellosis is a public health problem because of pathogenicity variability in strains for virulence factors. This study aimed to identify the virulence genes in Salmonella isolates from humans, crocodiles, broiler cloacas, and broiler carcasses from two departments of Colombia.

Materials and Methods

This study was conducted on 31 Salmonella enterica strains from humans with gastroenteritis (seven), crocodiles (seven), broiler cloacas (six), and broiler carcasses (12) from Tolima and Santander departments of Colombia, belonging to 21 serotypes. All samples were tested for Salmonella spp. using culture method on selective and non-selective mediums. Extraction of genomic DNA was performed from fresh colonies, DNA quality was verified by spectrophotometry and confirmed by amplification of InvA gene using conventional polymerase chain reaction (PCR). bapA, fimA, icmF, IroB, marT, mgtC, nlpI, oafA, pagN, siiD, spvC, spvR, spvB, Stn, and vexA genes were amplified by PCR.

Results

The most prevalent gene was bapA (100%), followed by marT (96.77%), mgtC (93.55%), and fimA (83.87%). Likewise, IroB (70.97%), Stn (67.74%), spvR (61.29%), pagN (54.84%), icmF (54.8%), and SiiD (45.16%) were positive for more than 50% of the strains. Furthermore, none of the isolates tested positive for the vexA gene. Salmonella isolates presented 26 virulence profiles.

Conclusion

This study reported 14 virulence genes in Salmonella spp. isolates from humans with gastroenteritis, crocodiles, and broiler cloacas and carcasses. The distribution of virulence genes differed among sources. This study could help in decision-making by health and sanitary authorities.

A Small RNA, SaaS, Promotes Salmonella Pathogenicity by Regulating Invasion, Intracellular Growth, and Virulence Factors

Salmonella enterica serovar Enteritidis is a common foodborne pathogen that infects both humans and animals. The S. Enteritidis virulence regulation network remains largely incomplete, and knowledge regarding the specific virulence phenotype of small RNAs (sRNAs) is limited. Here, we investigated the role of a previously identified sRNA, Salmonella adhesive-associated sRNA (SaaS), in the virulence phenotype of S. Enteritidis by constructing mutant (ΔsaaS) and complemented (ΔsaaS/psaaS) strains. SaaS did not affect S. Enteritidis; it was activated in the simulated intestinal environment (SIE), regulating the expression of virulence target genes. We discovered that it directly binds ssaV mRNA. Caco-2 and RAW 264.7 cell assays revealed that SaaS promoted S. Enteritidis invasion and damage to epithelial cells while suppressing macrophage overgrowth and destruction. Furthermore, a BALB/c mouse model demonstrated that the deletion of SaaS significantly reduced mortality and attenuated the deterioration of pathophysiology, bacterial dissemination into systemic circulation, and systemic inflammation. Our findings indicate that SaaS is required for S. Enteritidis virulence and further highlight its biological role in bacterial pathogenesis. IMPORTANCE Salmonella is a zoonotic pathogen with high virulence worldwide, and sRNAs have recently been discovered to play important roles. We explored the biological characteristics of the sRNA SaaS and developed two cell infection models and a mouse infection model. SaaS is an SIE-responsive sRNA that regulates the expression of virulence-targeted genes. Additionally, it differentially mediates invasion and intracellular growth for survival and infection of the epithelium and macrophages. We further found that SaaS enhanced bacterial virulence by promoting lethality, colonization, and inflammatory response. These findings provide a better understanding of the critical role of sRNA in bacterial virulence.

RyhB in Avian Pathogenic Escherichia coli Regulates the Expression of Virulence-Related Genes and Contributes to Meningitis Development in a Mouse Model

Avian pathogenic Escherichia coli (APEC) is an important member of extraintestinal pathogenic Escherichia coli (ExPEC). It shares similar pathogenic strategies with neonatal meningitis E. coli (NMEC) and may threaten human health due to its potential zoonosis. RyhB is a small non-coding RNA that regulates iron homeostasis in E. coli. However, it is unclear whether RyhB regulates meningitis occurrence. To investigate the function of RyhB in the development of meningitis, we constructed the deletion mutant APEC XM∆ryhB and the complemented mutant APEC XM∆ryhB/pryhB, established a mouse meningitis model and evaluated the role of RyhB in virulence of APEC. The results showed that the deletion of ryhB decreased biofilm formation, adhesion to the brain microvascular endothelial cell line bEnd.3 and serum resistance. RNA-seq data showed that the expression of multiple virulence-related genes changed in the ryhB deletion mutant in the presence of duck serum. Deletion of ryhB reduced the clinical symptoms of mice, such as opisthotonus, diarrhea and neurological signs, when challenged with APEC. Compared with the mice infected with the wild-type APEC, fewer histopathological lesions were observed in the brain of mice infected with the ryhB deletion mutant APEC XM∆ryhB. The bacterial loads in the tissues and the relative expression of cytokines (IL-1β, IL-6, and TNF-α) in the brain significantly decreased when challenged with the APEC XM∆ryhB. The expressions of tight junction proteins (claudin-5, occludin and ZO-1) were not reduced in the brain of mice infected with APEC XM∆ryhB; that is, the blood-brain barrier permeability of mice was not significantly damaged. In conclusion, RyhB contributes to the pathogenicity of APEC XM in the meningitis-causing process by promoting biofilm formation, adhesion to endothelial cells, serum resistance and virulence-related genes expression.

The salmonella effector Hcp modulates infection response, and affects salmonella adhesion and egg contamination incidences in ducks

Salmonella Entertidis (SE) often causes persistent infections and egg contamination in laying ducks. Hcp, the core structural and effector proteins of the Type VI Secretion System (T6SS) in SE, contributes to bacterial invasion, adhesion and virulence. However, little is known about the effect of Hcp on the host’s infection responses and egg contamination incidences in duck. Herein, we generated an hcp deletion mutant SE MY1△hcp and detected its ability to invade duck granulosa cells (dGCs) and contaminate eggs. In comparison with MY1-infected group, the SE adhesion decreased by 15.96% in MY1△hcp-infected dGCs, and the apoptosis in MY1△hcp-infected dGCs decreased by 26.58% and 30.99% at 3 and 6 hours postinfection, respectively. However, the expression levels of immunogenic genes TLR4, NOD1, TNFα, IL-1β and proinflammatory cytokines IL-6, IL-1β, TNF-α release were markedly lower in the dGCs inoculated with MY1△hcp than that of the wild type. Besides, the laying ducks were challenged with MY1 or MY1△hcp in vivo, respectively. The lower egg production and higher egg contamination were observed in MY1-infected ducks in comparison with MY1△hcp-infected birds. Furthermore, the host’s infection response of differentially abundant proteins (DAPs) to Salmonella effector Hcp was identified using quantitative proteomics. A total of 164 DAPs were identified between the MY1- and MY1△hcp-infected cells, which were mainly engaged in the immune, hormone synthesis, cell proliferation and cell apoptotic process. Among them, STAT3, AKT1, MAPK9, MAPK14, and CREBBP were the center of the regulatory network, which might serve as key host response regulators to bacterial Hcp. In conclusion, we demonstrated that effector Hcp contributed to not only SE invasion, induction of dGCs apoptosis, and trigger of immune responses, but also enhanced contamination incidences. Also, the STAT3, AKT1, MAPK9, MAPK14, and CREBBP were identified as host’s infection response regulators of bacterial Hcp in duck. Overall, these results not only offered a novel evidence of SE ovarian transmission but also identified some promising candidate regulators during SE infection.

Functions of Small Non-Coding RNAs in Salmonella–Host Interactions

Simple Summary

In the process of infecting the host, Salmonella senses and adapts to the environment within the host, breaks through the host’s defense system, and survives and multiplies in the host cell. As a class of universal regulators encoded in intergenic space, an increasing number of small non-coding RNAs (sRNAs) have been found to be involved in a series of processes during Salmonella infection, and they play an important role in interactions with the host cell. In this review, we discuss how sRNAs help Salmonella resist acidic environmental stress by regulating acid resistance genes and modulate adhesion and invasion to non-phagocytic cells by regulating virulent genes such as fimbrial subunits and outer membrane proteins. In addition, sRNAs help Salmonella adapt to oxidative stress within host cells and promote survival within macrophages. Although the function of a variety of sRNAs has been studied during host–Salmonella interactions, many of sRNAs’ functions remain to be discovered.

Abstract

Salmonella species infect hosts by entering phagocytic and non-phagocytic cells, causing diverse disease symptoms, such as fever, gastroenteritis, and even death. Therefore, Salmonella has attracted much attention. Many factors are involved in pathogenesis, for example, the capsule, enterotoxins, Salmonella pathogenicity islands (SPIs), and corresponding regulators. These factors are all traditional proteins associated with virulence and regulation. Recently, small non-coding RNAs (sRNAs) have also been reported to function as critical regulators. Salmonella has become a model organism for studying sRNAs. sRNAs regulate gene expression by imperfect base-pairing with targets at the post-transcriptional level. sRNAs are involved in diverse biological processes, such as virulence, substance metabolism, and adaptation to stress environments. Although some studies have reported the crucial roles of sRNAs in regulating host–pathogen interactions, the function of sRNAs in host–Salmonella interactions has rarely been reviewed. Here, we review the functions of sRNAs during the infection of host cells by Salmonella, aiming to deepen our understanding of sRNA functions and the pathogenic mechanism of Salmonella.

Phosphopantetheinyl transferase ClbA contributes to the virulence of avian pathogenic Escherichia coli in meningitis infection of mice

Avian pathogenic Escherichia coli (APEC), which has potential zoonotic risk, can cause severe systemic infections such as septicemia and meningitis in poultry. Colibactin is a hybrid non-ribosomal peptide/polyketide secondary metabolite produced by bacteria, which induces double-strand DNA breaks and chromosome instability in eukaryotic cells. ClbA is a 4’-phosphopantetheinyl transferase (PPTase) that is essential for colibactin and plays a role in siderophore synthesis. However, whether ClbA is associated with meningitis development in APEC is unclear. In this study, we abolished the clbA gene in the APEC XM strain, investigated the effect of clbA on colibactin synthesis and evaluated the pathogenic capacity of colibactin on meningitis development. Deletion of clbA reduced DNA damage to cells and hindered the normal synthesis of colibactin. Compared with the mice infected by wild-type APEC XM, the clbA deletion mutant infected mice had significant reduction in a series of characteristics associated with meningitis including clinical symptoms, bacterial loads of blood and brain, disruption of the blood brain barrier and the expression of inflammatory factors in the brain tissue. Complementation of ClbA recovered some APEC XM virulence. We conclude that ClbA is obligatory for the synthesis of colibactin and is responsible for the development of meningitis in mice infected by APEC.

Evaluation of Newcastle disease virus vaccine effectiveness in dogs with neurological signs of canine distemper

Canine Distemper Virus (CDV) is the cause of a highly lethal infectious disease affecting a broad range of carnivores. Despite using various treatments, there is still no effective treatment, especially in the neurological form of distemper. The aim of this study was to evaluate the therapeutic effect of injecting Newcastle disease vaccine into the subarachnoid space of dogs with neurological form of distemper. The dogs that had symptoms of nervous distemper, particularly myoclonus, were included in the plan. After anesthetizing of dogs, 0.10 to 1.00 mL of cerebrospinal fluid (CSF) were removed and, 0.10 to 0.50 mL of the prepared Newcastle solution were injected into their subarachnoid space. Another 0.50 to 1.00 mL of normal saline was then injected to remove the needle from the vaccine. The live attenuated LaSota or B1 vaccine was used in this study. Rapid kit tests and reverse transcription polymerase chain reaction (RT-PCR) assays were used to diagnose of the disease. Dogs were monitored for up to 3 to 24 months during that time they were evaluated for improvement or worsening of clinical symptoms. Out of nine dogs in which distemper were diagnosed with different tests, one dog recovered completely and another dog recovered greatly. Therefore, the overall recovery rate was 22.20%. It is concluded that administration of Newcastle vaccine into the subarachnoid space of dogs with nervous distemper causes at least 22.20% improvement and does not cause specific side effects and can be used to treat affected dogs.

Positive regulation of Type III secretion effectors and virulence by RyhB paralogs in Salmonella enterica serovar Enteritidis

Small non-coding RNA RyhB is a key regulator of iron homeostasis in bacteria by sensing iron availability in the environment. Although RyhB is known to influence bacterial virulence by interacting with iron metabolism related regulators, its interaction with virulence genes, especially the Type III secretion system (T3SS), has not been reported. Here, we demonstrate that two RyhB paralogs of Salmonella enterica serovar Enteritidis upregulate Type III secretion system (T3SS) effectors, and consequently affect Salmonella invasion into intestinal epithelial cells. Specifically, we found that RyhB-1 modulate Salmonella response to stress condition of iron deficiency and hypoxia, and stress in simulated intestinal environment (SIE). Under SIE culture conditions, both RyhB-1 and RyhB-2 are drastically induced and directly upregulate the expression of T3SS effector gene sipA by interacting with its 5′ untranslated region (5′ UTR) via an incomplete base-pairing mechanism. In addition, the RyhB paralogs upregulate the expression of T3SS effector gene sopE. By regulating the invasion-related genes, RyhBs in turn affect the ability of S. Enteritidis to adhere to and invade into intestinal epithelial cells. Our findings provide evidence that RyhBs function as critical virulence factors by directly regulating virulence-related gene expression. Thus, inhibition of RyhBs may be a potential strategy to attenuate Salmonella.

Targeting effect of berberine on type I fimbriae of Salmonella Typhimurium and its effective inhibition of biofilm

As a primary cause of food contamination and human diseases, Salmonella Typhimurium can easily form a biofilm that is difficult to remove from food surfaces, and often causes significant invisible threats to food safety. Although berberine has been widely used as an anti-infective drug in traditional medicine, some basic principles underlying its mechanism, especially the interaction between berberine and type I fimbriae genes, has not been verified yet. In this study, two strains of major fimbrial gene mutants (ΔfimA and ΔfimH) were constructed to demonstrate the possible action of berberine on type I fimbriae genes. The broth microdilution method was used to determine the antibacterial activity of berberine against selected strains (WT, ΔfimA, and ΔfimH). Cell agglutination experiments revealed that the number of S. Typhimurium type I fimbriae reduced after berberine treatment, which was consistent with transmission electron microscopy results. Quantitative real-time PCR experiments also confirmed that berberine reduced fimA gene expression, indicating a certain interaction between berberine and fimA gene. Furthermore, confocal laser scanning microscopy imaging of biofilm clearly revealed that berberine prevents biofilm formation by reducing the number of type I fimbriae. Overall, it is well speculated for us that berberine could be an excellent combating-biofilm drug in clinical microbiology and food preservation. KEY POINTS: • Reduce the number of fimbriae. • Berberine targeting fimA. • Effective biofilm inhibitor.