Hierarchical determinants in cytotoxic necrotizing factor (CNF) toxins driving Rho G-protein deamidation versus transglutamination

The cytotoxic necrotizing factor (CNF) family of AB-type bacterial protein toxins catalyze two types of modification on their Rho GTPase substrates: deamidation and transglutamination. It has been established that E. coli CNF1 and its close homolog proteins catalyze primarily deamidation and Bordetella dermonecrotic toxin (DNT) catalyzes primarily transglutamination. The rapidly expanding microbial genome sequencing data have revealed that there are at least 13 full-length variants of CNF1 homologs. CNFx from E. coli strain GN02091 is the most distant from all other members of the CNF family with 50%-55% sequence identity at the protein level and 0.45-0.52 nucleotide substitutions per site at the DNA level. CNFx modifies RhoA, Rac1, and Cdc42, and like CNF1, activates downstream SRE-dependent mitogenic signaling pathways in human HEK293T cells, but at a 1,000-fold higher EC50 value. Unlike other previously characterized CNF toxins, CNFx modifies Rho proteins primarily through transglutamination, as evidenced by gel-shift assay and confirmed by MALDI mass spectral analysis, when coexpressed with Rho-protein substrates in E. coli BL21 cells or through direct treatment of HEK293T cells. A comparison of CNF1 and CNFx sequences identified two critical active-site residues corresponding to positions 832 and 862 in CNF1. Reciprocal site-specific mutations at these residues in each toxin revealed hierarchical rules that define the preference for deamidase versus a transglutaminase activity in CNFs. An additional unique Cys residue at the C-terminus of CNFx was also discovered to be critical for retarding cargo delivery.IMPORTANCECytotoxic necrotizing factor (CNF) toxins not only play important virulence roles in pathogenic E. coli and other bacterial pathogens, but CNF-like genes have also been found in an expanding number of genomes from clinical isolates. Harnessing the power of evolutionary relationships among the CNF toxins enabled the deciphering of the hierarchical active-site determinants that define whether they modify their Rho GTPase substrates through deamidation or transglutamination. With our finding that a distant CNF variant (CNFx) unlike other known CNFs predominantly transglutaminates its Rho GTPase substrates, the paradigm of "CNFs deamidate and DNTs transglutaminate" could finally be attributed to two critical amino acid residues within the active site other than the previously identified catalytic Cys-His dyad residues. The significance of our approach and research findings is that they can be applied to deciphering enzyme reaction determinants and substrate specificities for other bacterial proteins in the development of precision therapeutic strategies.

Investigational Microbiological Therapy for Glioma

Glioma is the most common primary malignancy of the central nervous system (CNS), and 50% of patients present with glioblastoma (GBM), which is the most aggressive type. Currently, the most popular therapies are progressive chemotherapy and treatment with temozolomide (TMZ), but the median survival of glioma patients is still low as a result of the emergence of drug resistance, so we urgently need to find new therapies. A growing number of studies have shown that the diversity, bioactivity, and manipulability of microorganisms make microbial therapy a promising approach for cancer treatment. However, the many studies on the research progress of microorganisms and their derivatives in the development and treatment of glioma are scattered, and nobody has yet provided a comprehensive summary of them. Therefore, in this paper, we review the research progress of microorganisms and their derivatives in the development and treatment of glioma and conclude that it is possible to treat glioma by exogenous microbial therapies and targeting the gut-brain axis. In this article, we discuss the prospects and pressing issues relating to these therapies with the aim of providing new ideas for the treatment of glioma.

Recent advances in microbial toxin-related strategies to combat cancer

It is a major concern to treat cancer successfully, due to the distinctive pathophysiology of cancer cells and the gradual manifestation of resistance. Specific action, adverse effects and development of resistance has prompted the urgent requirement of exploring alternative anti-tumour treatment therapies. The naturally derived microbial toxins as a therapy against cancer cells are a promisingly new dimension. Various important microbial toxins such as Diphtheria toxin, Vibrio cholera toxin, Aflatoxin, Patulin, Cryptophycin-55, Chlorella are derived from several bacterial, fungal and algal species. These agents act on different biotargets such as inhibition of protein synthesis, reduction in cell growth, regulation of cell cycle and many cellular processes. Bacterial toxins produce actions primarily by targeting protein moieties and some immunomodulation and few acts through DNA. Fungal toxins appear to have more DNA damaging activity and affect the cell cycle. Algal toxins produce alteration in mitochondrial phosphorylation. In conclusion, microbial toxins and their metabolites appear to have a great potential to provide a promising option for the treatment and management to combat cancer.

The Role of Cyclomodulins and Some Microbial Metabolites in Bacterial Microecology and Macroorganism Carcinogenesis

A number of bacteria that colonize the human body produce toxins and effectors that cause changes in the eukaryotic cell cycle—cyclomodulins and low-molecular-weight compounds such as butyrate, lactic acid, and secondary bile acids. Cyclomodulins and metabolites are necessary for bacteria as adaptation factors—which are influenced by direct selection—to the ecological niches of the host. In the process of establishing two-way communication with the macroorganism, these compounds cause limited damage to the host, despite their ability to disrupt key processes in eukaryotic cells, which can lead to pathological changes. Possible negative consequences of cyclomodulin and metabolite actions include their potential role in carcinogenesis, in particular, with the ability to cause DNA damage, increase genome instability, and interfere with cancer-associated regulatory pathways. In this review, we aim to examine cyclomodulins and bacterial metabolites as important factors in bacterial survival and interaction with the host organism to show their heterogeneous effect on oncogenesis depending on the surrounding microenvironment, pathological conditions, and host genetic background.

Safest Roasting Times of Coffee To Reduce Carcinogenicity

ABSTRACT

Roasting coffee results in not only the creation of carcinogens such as acrylamide, furan, and polycyclic aromatic hydrocarbons but also the elimination of carcinogens in raw coffee beans, such as endotoxins, preservatives, or pesticides, by burning off. However, it has not been determined whether the concentrations of these carcinogens are sufficient to make either light or dark roast coffee more carcinogenic in a living organism. An Ames test was conducted on light, medium, and dark roast coffee from three origins. We found that lighter roast coffee shows higher mutagenicity, which is reduced to the control level in dark roast coffee varieties, indicating that the roasting process is not increasing mutagenic potential but is beneficial to eliminating the existing carcinogens in raw coffee beans. This result suggests that dark roast coffee is safer and promotes further studies of the various carcinogens in raw coffee that have been burned off.

HIGHLIGHTS

Gastrointestinal tumors and infectious agents: A wide field to explore

Infection is currently one of the main contributors to carcinogenesis. In fact, the International Agency for Research on Cancer has categorized eleven biological agents as group I carcinogens. It is estimated that around 16% of the 12.7 million new cancers diagnosed in 2008 were attributable to infectious agents. Although underdeveloped regions carry the highest incidence rates, about 7.4% of infection-related cancer cases occur in developed areas. Physicians are increasingly aware of the potential carcinogenic role of common virus like the Human Papilloma virus in cervical cancer, or the hepatitis B and C viruses in hepatocarcinoma. However, the carcinogenic role of several other infectious agents is less recognized. Given that gastrointestinal malignancies carry an overall poor prognosis, a better understanding of the carcinogenic mechanisms triggered by infectious agents is key to decrease the rate of cancer related deaths. Preventive measures directed to such infections would ideally impact survival. In this paper we review the main pathogenic mechanisms related to the development of gastrointestinal malignancies induced by infectious microorganisms and other pathogens which are currently under investigation.

From DNA Damage to Cancer Progression: Potential Effects of Cytolethal Distending Toxin

Cytolethal distending toxin (CDT), one of the most important genotoxins, is produced by several gram-negative bacteria and is involved in bacterial pathogenesis. Recent studies have shown that bacteria producing this peculiar genotoxin target host DNA, which potentially contributes to development of cancer. In this review, we highlighted the recent studies focusing on the idea that CDT leads to DNA damage, and the cells with inappropriately repaired DNA continue cycling, resulting in cancer development. Understanding the detailed mechanisms of genotoxins that cause DNA damage might be useful for targeting potential markers that drive cancer progression and help to discover new therapeutic strategies to prevent diseases caused by pathogens.

Cytolethal distending toxin: from genotoxin to a potential biomarker and anti-tumor target

Cytolethal Distending Toxin (CDT) belongs to the AB toxin family and is produced by a plethora of Gram-negative bacteria. Eight human-affecting enteropathogens harbor CDT that causes irritable bowel syndrome (IBS), dysentery, chancroid, and periodontitis worldwide. They have a novel molecular mode of action as they interfere in the eukaryotic cell-cycle progression leading to G₂/M arrest and apoptosis. CDT, the first bacterial genotoxin described, is encoded in a single operon possessing three proteins, CdtA, CdtB, and CdtC. CdtA and CdtC are needed for the binding of the CDT toxin complex to the cholesterol-rich lipid domains of the host cell while the CdtB is the active moiety. Sequence and 3D structural-based analysis of CdtB showed similarities with nucleases and phosphatases, it was hypothesized that CdtB exercises a biochemical function identical to both these enzymes. CDT is secreted through the outer membrane vesicles from the producing bacteria. It is internalized in the target cells via clathrin-dependent endocytosis and translocated to the host cell nucleus through the Golgi complex and ER. This study discusses the virulence role of CDT, causing pathogenicity by acting as a tri-perditious complex in the CDT-producing species with an emphasis on its potential role as a biomarker and an anti-tumor agent.

Microbiota Effects on Carcinogenesis: Initiation, Promotion, and Progression

Carcinogenesis is a multistep process by which normal cells acquire genetic and epigenetic changes that result in cancer. In combination with host genetic susceptibility and environmental exposures, a prominent procarcinogenic role for the microbiota has recently emerged. In colorectal cancer (CRC), three nefarious microbes have been consistently linked to cancer development: (a) Colibactin-producing Escherichia coli initiates carcinogenic DNA damage, (b) enterotoxigenic Bacteroides fragilis promotes tumorigenesis via toxin-induced cell proliferation and tumor-promoting inflammation, and (c) Fusobacterium nucleatum enhances CRC progression through two adhesins, Fap2 and FadA, that promote proliferation and antitumor immune evasion and may contribute to metastases. Herein, we use these three prominent microbes to discuss the experimental evidence linking microbial activities to carcinogenesis and the specific mechanisms driving this stepwise process. Precisely defining mechanisms by which the microbiota impacts carcinogenesis at each stage is essential for developing microbiota-targeted strategies for the diagnosis, prognosis, and treatment of cancer.

Gut Microbiota and Colon Cancer: A Role for Bacterial Protein Toxins?

Accumulating evidence indicates that the human intestinal microbiota can contribute to the etiology of colorectal cancer. Triggering factors, including inflammation and bacterial infections, may favor the shift of the gut microbiota from a mutualistic to a pro-carcinogenic configuration. In this context, certain bacterial pathogens can exert a pro-tumoral activity by producing enzymatically-active protein toxins that either directly induce host cell DNA damage or interfere with essential host cell signaling pathways involved in cell proliferation, apoptosis, and inflammation. This review is focused on those toxins that, by mimicking carcinogens and cancer promoters, could represent a paradigm for bacterially induced carcinogenesis.

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.

Prospects of NSAIDs administration as double-edged agents against endometrial cancer and pathological species of the uterine microbiome

Many types of cancers, including endometrial cancer, were found to have cyclooxygenase-2 (COX-2) overexpression. Because this enzyme belongs to the group of pro-inflammatory enzymes, so-called NSAIDs (non-steroidal anti–inflammatory drugs) directly inhibit its activity. An increasing number of reports on COX-2 involvement in cancer, as well as on the role of microbiota in abnormal metabolism and signaling of cells, forces the development of new NSAID types. Besides, NSAIDs can affect some bacteria, which are vaginal/endometrial microbiome members. The overgrowth of those species was found to be a major cause of some uterus diseases. Those infections can lead to chronic inflammatory response and suppress anti-tumorigenic cell pathways. The purpose of this review is to highlight the COX-2 enzyme role in endometrial cancer, the potential effect of the endometrial microbiome on COX-2 enzyme overexpression, and the prospects of NSAIDs use in terms of this type of cancer.

Hernandez R, T. Erira A, Kandaurova L, L. Juarez C, Juarez V, Cid-Arregui A. Oral Microbiota Associated with Oral and Gastroenteric Cancer

When the normal microbiota-host interactions are altered, the commensal microbial community evolves to a dysbiotic status resulting in some species becoming pathogenic and acting synergistically in the development of local and systemic diseases, including cancer. Advances in genetics, immunology and microbiology during the last years have made it possible to gather information on the oral and gastrointestinal microbiome and its interaction with the host, which has led to a better understanding of the interrelationship between microbiota and cancer. There is growing evidence in support for the role of some species in the development, progression and responses to treatment of various types of cancer. Accordingly, the number of studies investigating the association between oral microbiota and oral and gastrointestinal cancers has increased significantly during the last years. Here, we review the literature documenting associations of oral microbiota with oral and gastroenteric cancers.

Cho W, Soleimanpour S. Bacteriotherapy in Breast Cancer

Breast cancer is the second most common cause of cancer-related mortality among women around the world. Conventional treatments in the fight against breast cancer, such as chemotherapy, are being challenged regarding their effectiveness. Thus, strategies for the treatment of breast cancer need to be continuously refined to achieve a better patient outcome. We know that a number of bacteria are pathogenic and some are even associated with tumor development, however, recent studies have demonstrated interesting results suggesting some bacteria may have potential for cancer therapy. Therefore, the therapeutic role of bacteria has aroused attention in medical and pharmaceutical studies. Furthermore, genetic engineering has been used in bacterial therapy and may led to greater efficacy with few side effects. Some genetically modified non-pathogenic bacterial species are more successful due to their selectivity for cancer cells but with low toxicity for normal cells. Some live, attenuated, or genetically modified bacterias are capable to multiply in tumors and inhibit their growth. This article aims to review the role of bacteria and their products including bacterial peptides, bacteriocins, and toxins for the treatment of breast cancer.

Intestinal colonization of genotoxic Escherichia coli strains encoding colibactin and cytotoxic necrotizing factor in small mammal pets

Escherichia coli encoding colibactin (clb), cytolethal distending toxin (cdt), and hemolysin-associated cytotoxic necrotizing factor (cnf) are associated with various intestinal and extra-intestinal diseases in humans and animals. Small mammal pets are not evaluated for genotoxin-encoding E. coli. Thus, the prevalence of such strains is unknown. The objective of this study was to isolate and characterize genotoxin-encoding E. coli from healthy and ill small mammal pets examined at a veterinary clinic and at two animal adoption centers. E. coli isolates were cultured from fecal samples and biochemically characterized. A total of 65 animals, including mice, rats, rabbits, guinea pigs, and hedgehogs, were screened. Twenty-six E. coli isolates were obtained from 24 animals. Twelve of the 26 isolates (46.2 %) were PCR-positive for the pks genes clbA and clbQ. Two isolates (7.7 %) were PCR-positive for cnf. All isolates were PCR-negative for cdt. All genotoxin-encoding isolates belonged to the pathogen-associated phylogenetic group B2. Representative genotoxin-encoding isolates had serotypes previously associated with clinical disease in humans and animals. Isolates encoding pks or cnf induced megalocytosis and cytotoxicity to HeLa cells in vitro. Although most isolates were obtained from healthy pets, two guinea pigs with diarrhea had pks-positive isolates cultured from their feces. Whole genome sequencing on four representative isolates confirmed the presence of pks and cnf genes and identified other virulence factors associated with pathogenicity in animals and humans. Our results suggest that small mammalian pets may serve as a reservoir for potentially pathogenic E. coli and implicate a zoonotic risk.

The Escherichia coli protein toxin cytotoxic necrotizing factor 1 induces epithelial mesenchymal transition

Some toxigenic bacteria produce protein toxins with carcinogenic signatures, which either directly damage DNA or stimulate signalling pathways related to cancer. So far, however, only a few of them have been proved to favour the induction or progression of cancer. In this work, we report that the Rho-activating Escherichia coli protein toxin, cytotoxic necrotising factor 1 (CNF1), induces epithelial to mesenchymal transition (EMT) in intestinal epithelial cells. EMT is a crucial step in malignant tumour conversion and invasiveness. In the case of CNF1, it occurs by up-regulation of the transcription factors ZEB1 and Snail1, delocalisation of E-cadherin and β-catenin, activation of the serine/threonine kinase mTOR, accelerated wound healing, and invasion. However, our results highlight that nontransformed epithelial cells entail the presence of inflammatory factors, in addition to CNF1, to acquire a mesenchymal-like behaviour. All this suggests that the surrounding microenvironment, as well as the cell type, dramatically influences the CNF1 ability to promote carcinogenic traits.

Current Knowledge of the Potential Links between Inflammation and Prostate Cancer

Inflammation is inherent in prostatic diseases and it is now accepted that it may facilitate cellular proliferation in both benign and malignant conditions. The strong relationship between prostatic inflammation and pathogenesis of benign prostatic hyperplasia (BPH) is supported by epidemiologic, histopathologic and molecular evidence. Contrariwise, the role of inflammation in prostate carcinogenesis is still controversial, although current data indicate that the inflammatory microenvironment can regulate prostate cancer (PCa) growth and progression. Knowledge of the complex molecular landscape associated with chronic inflammation in the context of PCa may lead to the introduction and optimization of novel targeted therapies. In this perspective, evaluation of the inflammatory component in prostate specimens could be included in routine pathology reports.

Genotoxic Escherichia coli Strains Encoding Colibactin, Cytolethal Distending Toxin, and Cytotoxic Necrotizing Factor in Laboratory Rats

Although many Escherichia coli strains are considered commensals in mammals, strains encoding the cyclomodulin genotoxins are associated with clinical and subclinical disease in the urogenital and gastrointestinal tracts, meningitis, and inflammatory disorders. These genotoxins include the polyketide synthase (pks) pathogenicity island, cytolethal distending toxin (cdt), and hemolysin-associated cytotoxic necrotizing factor (cnf). E. coli strains are not excluded from rodents housed under SPF conditions in academic or vendor facilities. This study isolated and characterized genotoxin-encoding E. coli from laboratory rats obtained from 4 academic institutions and 3 vendors. A total of 69 distinct E. coli isolates were cultured from feces, rectal swab, nares, or vaginal swab of 52 rats and characterized biochemically. PCR analysis for cyclomodulin genes and phylogroup was performed on all 69 isolates. Of the 69 isolates, 45 (65%) were positive for pks, 20/69 (29%) were positive for cdt, and 4 (6%) were positive for cnf. Colibactin was the sole genotoxin identified in 21 of 45 pks+ isolates (47%), whereas cdt or cnf was also present in the remaining 24 isolates (53%); cdt and cnf were never present together or without pks. All genotoxin-associated strains were members of pathogen-associated phylogroup B2. Fisher exact and χ² tests demonstrated significant differences in genotoxin prevalence and API code distribution with regard to vendor. Select E. coli isolates were characterized by HeLa cell in vitro cytotoxicity assays, serotyped, and whole-genome sequenced. All isolates encoding cyclomodulins induced megalocytosis. Serotypes corresponded with vendor origin and cyclomodulin composition, with the cnf+ serotype representing a known human uropathogen. Whole-genome sequencing confirmed the presence of complete pks, cdt, and hemolysin-cnf pathogenicity islands. These findings indicate that genotoxin-encoding E. coli colonize laboratory rats from multiple commercial vendors and academic institutions and suggest the potential to contribute to clinical disease and introduce confounding variables into experimental rat models.

Bacterial infections and cancer

Infections are estimated to contribute to 20% of all human tumours. These are mainly caused by viruses, which explains why a direct bacterial contribution to cancer formation has been largely ignored. While epidemiological data link bacterial infections to particular cancers, tumour formation is generally assumed to be solely caused by the ensuing inflammation responses. Yet, many bacteria directly manipulate their host cell in various phases of their infection cycle. Such manipulations can affect host cell integrity and can contribute to cancer formation. We here describe how bacterial surface moieties, bacterial protein toxins and bacterial effector proteins can induce host cell DNA damage, and thereby can interfere with essential host cell signalling pathways involved in cell proliferation, apoptosis, differentiation and immune signalling.

Bacterial Toxins and Targeted Brain Therapy: New Insights from Cytotoxic Necrotizing Factor 1 (CNF1)

Pathogenic bacteria produce toxins to promote host invasion and, therefore, their survival. The extreme potency and specificity of these toxins confer to this category of proteins an exceptionally strong potential for therapeutic exploitation. In this review, we deal with cytotoxic necrotizing factor (CNF1), a cytotoxin produced by Escherichia coli affecting fundamental cellular processes, including cytoskeletal dynamics, cell cycle progression, transcriptional regulation, cell survival and migration. First, we provide an overview of the mechanisms of action of CNF1 in target cells. Next, we focus on the potential use of CNF1 as a pharmacological treatment in central nervous system’s diseases. CNF1 appears to impact neuronal morphology, physiology, and plasticity and displays an antineoplastic activity on brain tumors. The ability to preserve neural functionality and, at the same time, to trigger senescence and death of proliferating glioma cells, makes CNF1 an encouraging new strategy for the treatment of brain tumors.

Heterogeneous Family of Cyclomodulins: Smart Weapons That Allow Bacteria to Hijack the Eukaryotic Cell Cycle and Promote Infections

Some bacterial pathogens modulate signaling pathways of eukaryotic cells in order to subvert the host response for their own benefit, leading to successful colonization and invasion. Pathogenic bacteria produce multiple compounds that generate favorable conditions to their survival and growth during infection in eukaryotic hosts. Many bacterial toxins can alter the cell cycle progression of host cells, impairing essential cellular functions and impeding host cell division. This review summarizes current knowledge regarding cyclomodulins, a heterogeneous family of bacterial effectors that induce eukaryotic cell cycle alterations. We discuss the mechanisms of actions of cyclomodulins according to their biochemical properties, providing examples of various cyclomodulins such as cycle inhibiting factor, γ-glutamyltranspeptidase, cytolethal distending toxins, shiga toxin, subtilase toxin, anthrax toxin, cholera toxin, adenylate cyclase toxins, vacuolating cytotoxin, cytotoxic necrotizing factor, Panton-Valentine leukocidin, phenol soluble modulins, and mycolactone. Special attention is paid to the benefit provided by cyclomodulins to bacteria during colonization of the host.

Microbiome and Anticancer Immunosurveillance

Anticancer immune responses can be considered a desirable form of autoimmunity that may be profoundly shaped by the microbiome. Here, we discuss evidence for the microbiome's influence on anti-tumor immunosurveillance, including those that are indirect and can act at a distance, and we put forward hypotheses regarding mechanisms of how these effects are implemented. These may involve cross-reactivity between microbial and tumor antigens shaping T cell repertoires and/or microbial products stimulating pattern recognition receptors that influence the type and intensity of immune responses. Understanding how the microbiome impacts natural cancer immunosurveillance as well as treatment-induced immune responses will pave the way for more effective therapies and prophylactics.

The Enterobacterial Genotoxins: Cytolethal Distending Toxin and Colibactin

While the DNA damage induced by ionizing radiation and by many chemical compounds and drugs is well characterized, the genotoxic insults inflicted by bacteria are only scarcely documented. However, accumulating evidence indicates that we are exposed to bacterial genotoxins. The prototypes of such bacterial genotoxins are the Cytolethal Distending Toxins (CDTs) produced by Escherichia coli and Salmonella enterica serovar Typhi. CDTs display the DNase structure fold and activity, and induce DNA strand breaks in the intoxicated host cell nuclei. E. coli and certain other Enterobacteriaceae species synthesize another genotoxin, colibactin. Colibactin is a secondary metabolite, a hybrid polyketide/nonribosomal peptide compound synthesized by a complex biosynthetic machinery. In this review, we summarize the current knowledge on CDT and colibactin produced by E. coli and/or Salmonella Typhi. We describe their prevalence, genetic determinants, modes of action, and impact in infectious diseases or gut colonization, and discuss the possible involvement of these genotoxigenic bacteria in cancer.

Use of Bacteria in Cancer Therapy

Cancer is one of the most dreaded diseases in humans and most common cause of death in twenty-first century. New cancer therapies are urgently required because of the existing pharmacological side effects of the conventional chemotherapy, radiation, or surgery. Newer modalities such as cancer vaccines and biological therapies are proving very helpful in the treatment of cancer along with the conventional therapies. The success of these novel cancer therapies is attributed to their lesser toxicity and the specific killing of the cancer cells. Bacterial therapy for cancer has been recognized a century ago. Live, attenuated, or genetically modified obligate or facultative anaerobic bacterial species exhibit the inherent property of colonizing the tumors and are capable of multiplying selectively inside the tumors, thereby inhibiting cancerous growths. The bacteria and their spores are used in the target specific therapies, delivering the prodrugs and the various proteins to the tumors. Albeit bacterial treatment of cancer is providing new perspective in the treatment of disease, the use of microorganisms to target tumors has certain confinements. The biosafety, genetic instability and the confounded interaction of the bacteria with treatment drugs, requires the more noteworthy consideration regarding the use of this novel treatment in the cancer treatment.