Dynamic Duo-The Salmonella Cytolethal Distending Toxin Combines ADP-Ribosyltransferase and Nuclease Activities in a Novel Form of the Cytolethal Distending Toxin

Hunted Wild Boars in Sardinia: Prevalence, Antimicrobial Resistance and Genomic Analysis of Salmonella and Yersinia enterocolitica

The objective of this investigation was to evaluate Salmonella and Yersinia enterocolitica prevalence in wild boars hunted in Sardinia and further characterize the isolates and analyse antimicrobial resistance (AMR) patterns. In order to assess slaughtering hygiene, an evaluation of carcasses microbial contamination was also carried out. Between 2020 and 2022, samples were collected from 66 wild boars hunted during two hunting seasons from the area of two provinces in northern and central Sardinia (Italy). Samples collected included colon content samples, mesenteric lymph nodes samples and carcass surface samples. Salmonella and Y. enterocolitica detection was conducted on each sample; also, on carcass surface samples, total aerobic mesophilic count and Enterobacteriaceae count were evaluated. On Salmonella and Y. enterocolitica isolates, antimicrobial susceptibility was tested and whole genome sequencing was applied. Salmonella was identified in the colon content samples of 3/66 (4.5%) wild boars; isolates were S. enterica subs. salamae, S. ser. elomrane and S. enterica subs. enterica. Y. enterocolitica was detected from 20/66 (30.3%) wild boars: in 18/66 (27.3%) colon contents, in 3/66 (4.5%) mesenteric lymph nodes and in 3/49 (6.1%) carcass surface samples. In all, 24 Y. enterocolitica isolates were analysed and 20 different sequence types were detected, with the most common being ST860. Regarding AMR, no resistance was detected in Salmonella isolates, while expected resistance towards β-lactams (blaA gene) and streptogramin (vatF gene) was observed in Y. enterocolitica isolates (91.7% and 4.2%, respectively). The low presence of AMR is probably due to the low anthropic impact in the wild areas. Regarding the surface contamination of carcasses, values (mean ± standard deviation log10 CFU/cm2) were 2.46 ± 0.97 for ACC and 1.07 ± 1.18 for Enterobacteriaceae. The results of our study confirm that wild boars can serve as reservoirs and spreaders of Salmonella and Y. enterocolitica; the finding of Y. enterocolitica presence on carcass surface highlights how meat may become superficially contaminated, especially considering that contamination is linked to the conditions related to the hunting, handling and processing of game animals.

Comprehensive Genomic Characterization of Antibiotic Resistance, Virulence, and Clonality in Salmonella Isolates from Wild Animals in Algeria

This study investigated Salmonella spp. in wild animals in Algeria, focusing on their prevalence, serotypes, antibiotic resistance, and virulence profiles. From fecal samples collected between May 2021 and June 2022, 1.9% showed Salmonella shedding. The identified serotypes included S. Bredeney, S. Enteritidis, S. Altona, and S. Virchow. Except for S. Altona, all isolates were resistant to quinolones, with S. Bredeney strains, exhibiting multidrug resistance. Whole-genome sequencing revealed various resistance genes and mutations in gyrA or parC genes. Additionally, plasmids IncX1 and ColpVC were detected in several isolates. A comprehensive analysis identified 201 virulence genes. These findings contribute to understanding Salmonella in wild animal populations and their potential impact on public health.

Genomic Diversity, Antimicrobial Resistance, Plasmidome, and Virulence Profiles of Salmonella Isolated from Small Specialty Crop Farms Revealed by Whole-Genome Sequencing

Salmonella is the leading cause of death associated with foodborne illnesses in the USA. Difficulty in treating human salmonellosis is attributed to the development of antimicrobial resistance and the pathogenicity of Salmonella strains. Therefore, it is important to study the genetic landscape of Salmonella, such as the diversity, plasmids, and presence antimicrobial resistance genes (AMRs) and virulence genes. To this end, we isolated Salmonella from environmental samples from small specialty crop farms (SSCFs) in Northeast Ohio from 2016 to 2021; 80 Salmonella isolates from 29 Salmonella-positive samples were subjected to whole-genome sequencing (WGS). In silico serotyping revealed the presence of 15 serotypes. AMR genes were detected in 15% of the samples, with 75% exhibiting phenotypic and genotypic multidrug resistance (MDR). Plasmid analysis demonstrated the presence of nine different types of plasmids, and 75% of AMR genes were located on plasmids. Interestingly, five Salmonella Newport isolates and one Salmonella Dublin isolate carried the ACSSuT gene cassette on a plasmid, which confers resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline. Overall, our results show that SSCFs are a potential reservoir of Salmonella with MDR genes. Thus, regular monitoring is needed to prevent the transmission of MDR Salmonella from SSCFs to humans.

Carriage of CdtB Encoding Campylobacter spp., Salmonella enterica, and Yersinia entercolitica in Patients with Gastroenteritis and Irritable Bowel Syndrome

INTRODUCTION

Cytolethal distending toxin (Cdt) is one of the bacterial toxins that present in a variety of gram-negative human pathogens, such as E. coli, Salmonella spp., and Campylobacter spp. CDT is composed of three subunits encoded by three adjacent genes, including cdtA, cdtB, and cdtC. cdtB has been shown to have toxic activity and cause DNA damage in host cells. Despite its presence in different bacterial species, the role of CdtB in acute and chronic infections, such as gastroenteritis and irritable bowel syndrome (IBS), is unclear. To analyze this correlation, we studied the prevalence of cdtB among different enteropathogenic bacteria in patients with gastroenteritis and IBS compared with healthy people.

MATERIALS AND METHODS

In this cross-sectional descriptive study, 230 stool samples were collected from patients with gastroenteritis, IBS, and healthy people. The presence of CdtB encoding bacteria, including Escherichia coli, Campylobacter spp., Yersinia entercolitica, Providencia alkalifacience, and Salmonella enterica, was examined by polymerase chain reaction using genus-specific primers.

RESULTS

Out of 230 stool samples, CdtB encoding Campylobacter spp. were found in 34.6% (52/150), 6.25% (5/80), and 4% (2/50) of the patients with gastroenteritis, IBS, and the control group, respectively. Carriage of CdtB encoding Salmonella enterica was characterized among 5.3% (8/150) of the patients with gastroenteritis and 17.5% (14/80) of the IBS patients. Although none of the patients carried CdtB encoding E. coli and Providencia spp., cdtB of Y. enterocolitica was detected in one of the patients with gastroenteritis (0.6%). Statistical analysis showed significant correlation between infection with CdtB encoding Campylobacter spp. and IBS-D subtype. No significant correlation was found between infection with CdtB encoding bacteria and other clinical and demographic data.

CONCLUSION

Our results confirmed a relatively higher frequency of CdtB encoding bacteria in the intestine of patients with gastroenteritis and those with IBS compared with healthy individuals. Regarding the frequency of CdtB encoding Salmonella and Campylobacter bacteria, it was proposed that infection with these enteropathogens could be considered a risk factor for the development or progression of IBS among Iranian patients. Further studies are needed to establish this involvement.

The Effect of Acute and Chronic Infection-Induced by AvrA Protein of Salmonella typhimurium on Radical Oxygen Species, Phosphatase and Tensin Homolog, and Cellular Homolog Expression During the Development of Colon Cancer

AIM. The aim of the study was to analyze Avra's effector in inducing cancer stem cells into colon cancer through increased radical oxygen species (ROS), PTEN expression and c-myC as markers of tumorigenesis in mice model of the colorectal cancer infected with S. typhimurium. METHODS. The study used balb c mice induced once a week by 10 mg / mL / day of AOM for 1-week and 12-week treatment period. Isolation of S. typhimurium specific protein had been carried out before being induced to mice in intraperitoneal manner in the amount of 40 mL / 50 mL. Propagation of S. typhimurium ATCC bacteria with MacConkey media and isolation of S. typhimurium protein were administered. The sample was divided into 4 groups, positive control group (group that was only exposed to azoxymethane (AOM), group exposed to both AOM and AvrA (AOM + AvrA), and group exposed to both AOM and S. typhimurium (AOM + S. typhimurium). Blood flow cytometry and soft tissue sampling for IHC and data analysis were then conducted. RESULTS. The results of the study showed that there was an increase in the expression of ROS, PTEN and c-Myc. Increased ROS expression was found in the 12-week treatment period group and it was known that such increase was due to AOM + S. typhimurium (45.78 ± 2.93) induction compared to AOM, AOM + AvrA and control (p <0.05). PTEN and C-myc expression increased at the 12th week compared to the negative control. CONCLUSION. Inflammation is the triggering factor for colorectal cancer, in which the expression of ROS, PTEN and c-Myc as the colorectal cancer markers increases in both the acute and chronic phases.

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

Colorectal cancer (CRC) incidence increases yearly, and is three to four times higher in developed countries compared to developing countries. The well-known risk factors have been attributed to low physical activity, overweight, obesity, dietary consumption including excessive consumption of red processed meats, alcohol, and low dietary fiber content. There is growing evidence of the interplay between diet and gut microbiota in CRC carcinogenesis. Although there appears to be a direct causal role for gut microbes in the development of CRC in some animal models, the link between diet, gut microbes, and colonic carcinogenesis has been established largely as an association rather than as a cause-and-effect relationship. This is especially true for human studies. As essential dietary factors influence CRC risk, the role of proteins, carbohydrates, fat, and their end products are considered as part of the interplay between diet and gut microbiota. The underlying molecular mechanisms of colon carcinogenesis mediated by gut microbiota are also discussed. Human biological responses such as inflammation, oxidative stress, deoxyribonucleic acid (DNA) damage can all influence dysbiosis and consequently CRC carcinogenesis. Dysbiosis could add to CRC risk by shifting the effect of dietary components toward promoting a colonic neoplasm together with interacting with gut microbiota. It follows that dietary intervention and gut microbiota modulation may play a vital role in reducing CRC risk.

Whole-Genome Sequences of Salmonella Isolates from an Ecological Wastewater Treatment System

Twenty-seven Salmonella isolates were collected from four locations within an ecological wastewater treatment system located at The Pennsylvania State University and were subjected to whole-genome sequencing. The sequences obtained were used for in silico characterization, including serotyping and phylogenetic relatedness analysis.

Twenty-seven Salmonella isolates were collected from four locations within an ecological wastewater treatment system located at The Pennsylvania State University and were subjected to whole-genome sequencing. The sequences obtained were used for in silico characterization, including serotyping and phylogenetic relatedness analysis.

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

Typhoid toxin exhausts the RPA response to DNA replication stress driving senescence and Salmonella infection

Salmonella Typhi activates the host DNA damage response through the typhoid toxin, facilitating typhoid symptoms and chronic infections. Here we reveal a non-canonical DNA damage response, which we call RING (response induced by a genotoxin), characterized by accumulation of phosphorylated histone H2AX (γH2AX) at the nuclear periphery. RING is the result of persistent DNA damage mediated by toxin nuclease activity and is characterized by hyperphosphorylation of RPA, a sensor of single-stranded DNA (ssDNA) and DNA replication stress. The toxin overloads the RPA pathway with ssDNA substrate, causing RPA exhaustion and senescence. Senescence is also induced by canonical γΗ2ΑΧ foci revealing distinct mechanisms. Senescence is transmitted to non-intoxicated bystander cells by an unidentified senescence-associated secreted factor that enhances Salmonella infections. Thus, our work uncovers a mechanism by which genotoxic Salmonella exhausts the RPA response by inducing ssDNA formation, driving host cell senescence and facilitating infection.

Distribution of virulence factors, determinants of antibiotic resistance and molecular fingerprinting of Salmonella species isolated from cattle and beef samples: suggestive evidence of animal-to-meat contamination

In this study, three hundred presumptive Salmonella strains isolated from cattle faeces and raw beef samples were subjected to both preliminary and confirmatory tests specific for Salmonella. PCR assays revealed that 100%, 20% and 26.7% of the isolates were positive for 16S rRNA, fliC and fljB gene fragments, respectively. Large proportions (62.4 to 94.3%) of these isolates were multiple antibiotic resistant (MAR) strains that were resistant to three or more antibiotics belonging to different classes. MAR phenotypes Ab1, Ab2, Ab3, Ab7, Ab8, Ab9, Ab26 and Ab27 were dominant among the isolates. Cluster analysis of antibiotic inhibition zone diameter data revealed two major clusters (clusters 1 and 2), and each cluster contained two sub-clusters (1A, 1B, 2A and 2B). PCR data revealed that 27.1% and 30.7% of the isolates possessed the spvC and invA virulent genes, respectively. There was a significant correlation between the possession of MAR phenotypes and virulent gene determinants. Analysis of restriction fragment length polymorphism (RFLP) of 16S rRNA gene fragments using EcoRI and HaeIII showed that large proportions of isolates from beef and cattle faeces produced similar genetic fingerprints. From these results, it is suggested that Salmonella species in cattle are transmitted to beef and, therefore, the consumption of undercooked beef could pose severe health complications on consumers. These findings provide baseline data that could be of great epidemiological importance and, thus, the need to utilise more sensitive typing tools in determining the genetic relatedness of isolates from different sources.

The Typhoid Toxin Produced by the Nontyphoidal Salmonella enterica Serotype Javiana Is Required for Induction of a DNA Damage Response In Vitro and Systemic Spread In Vivo

The Salmonella cytolethal distending toxin (S-CDT), first described as the “typhoid toxin” in Salmonella enterica subsp. enterica serotype Typhi, induces DNA damage in eukaryotic cells. Recent studies have shown that more than 40 nontyphoidal Salmonella (NTS) serotypes carry genes that encode S-CDT, yet very little is known about the activity, function, and role of S-CDT in NTS. Here we show that deletion of genes encoding the binding subunit (pltB) and a bacteriophage muramidase predicted to play a role in toxin export (ttsA) does not abolish toxin activity in the S-CDT-positive NTS Salmonella enterica subsp. enterica serotype Javiana. However, S. Javiana strains harboring deletions of both pltB and its homolog artB, had a complete loss of S-CDT activity, suggesting that S. Javiana carries genes encoding two variants of the binding subunit. S-CDT-mediated DNA damage, as determined by phosphorylation of histone 2AX (H2AX), producing phosphorylated H2AX (γH2AX), was restricted to epithelial cells in S and G₂/M phases of the cell cycle and did not result in apoptosis or cell death. Compared to mice infected with a ΔcdtB strain, mice infected with wild-type S. Javiana had significantly higher levels of S. Javiana in the liver, but not in the spleen, ileum, or cecum. Overall, we show that production of active S-CDT by NTS serotype S. Javiana requires different genes (cdtB, pltA, and either pltB or artB) for expression of biologically active toxin than those reported for S-CDT production by S. Typhi (cdtB, pltA, pltB, and ttsA). However, as in S. Typhi, NTS S-CDT influences the outcome of infection both in vitro and in vivo.

Nontyphoidal Salmonella (NTS) are a major cause of bacterial food-borne illness worldwide; however, our understanding of virulence mechanisms that determine the outcome and severity of nontyphoidal salmonellosis is incompletely understood. Here we show that S-CDT produced by NTS plays a significant role in the outcome of infection both in vitro and in vivo, highlighting S-CDT as an important virulence factor for nontyphoidal Salmonella serotypes. Our data also contribute novel information about the function of S-CDT, as S-CDT-mediated DNA damage occurs only during certain phases of the cell cycle, and the resulting damage does not induce cell death as assessed using a propidium iodide exclusion assay. Importantly, our data support that, despite having genetically similar S-CDT operons, NTS serotype S. Javiana has different genetic requirements than S. Typhi, for the production and export of active S-CDT.

Biofilm Producing Salmonella Typhi: Chronic Colonization and Development of Gallbladder Cancer

Salmonella enterica subspecies enterica serovar Typhi is the aetiological agent of typhoid or enteric fever. In a subset of individuals, S. Typhi colonizes the gallbladder causing an asymptomatic chronic infection. Nonetheless, these asymptomatic carriers provide a reservoir for further spreading of the disease. Epidemiological studies performed in regions where S. Typhi is endemic, revealed that the majority of chronically infected carriers also harbour gallstones, which in turn, have been indicated as a primary predisposing factor for the onset of gallbladder cancer (GC). It is now well recognised, that S. Typhi produces a typhoid toxin with a carcinogenic potential, that induces DNA damage and cell cycle alterations in intoxicated cells. In addition, biofilm production by S. Typhi may represent a key factor for the promotion of a persistent infection in the gallbladder, thus sustaining a chronic local inflammatory response and exposing the epithelium to repeated damage caused by carcinogenic toxins. This review aims to highlight the putative connection between the chronic colonization by highly pathogenic strains of S. Typhi capable of combining biofilm and toxin production and the onset of GC. Considering the high risk of GC associated with the asymptomatic carrier status, the rapid identification and profiling of biofilm production by S. Typhi strains would be key for effective therapeutic management and cancer prevention.

Towards Engineering Novel PE-Based Immunotoxins by Targeting Them to the Nucleus

Exotoxin A (PE) from Pseudomonas aeruginosa is a bacterial ADP-ribosyltransferase, which can permanently inhibit translation in the attacked cells. Consequently, this toxin is frequently used in immunotoxins for targeted cancer therapies. In this study, we propose a novel modification to PE by incorporating the NLS sequence at its C-terminus, to make it a selective agent against fast-proliferating cancer cells, as a nucleus-accumulated toxin should be separated from its natural substrate (eEF2) in slowly dividing cells. Here, we report the cytotoxic activity and selected biochemical properties of newly designed PE mutein using two cellular models: A549 and HepG2. We also present a newly developed protocol for efficient purification of recombinant PE and its muteins with very high purity and activity. We found that furin cleavage is not critical for the activity of PE in the analyzed cell lines. Surprisingly, we observed increased toxicity of the toxin accumulated in the nucleus. This might be explained by unexpected nuclease activity of PE and its potential ability to cleave chromosomal DNA, which seems to be a putative alternative intoxication mechanism. Further experimental investigations should address this newly detected activity to identify catalytic residues and elucidate the molecular mechanism responsible for this action.