Psychoactive Drugs Induce the SOS Response and Shiga Toxin Production in Escherichia coli

Rapid assembly of biofilms from DNA released by SOS-inducing drugs in enteric bacteria

The SOS response is a bacterial stress response activated by DNA damage in many types of bacteria. SOS-inducing antibiotics trigger the rapid release of DNA into the extracellular medium in many strains. Surprisingly, the DNA released in this way contains greater amounts of single-stranded DNA (ssDNA) than double-stranded DNA (dsDNA). In this study, we observed that addition of DNA-binding proteins following induction of the SOS response in Enterobacter cloacae decreased the amount of DNA measurable in the supernatant medium, but increased the amount of DNA deposited as a biofilm at the air-fluid interface. Bacteria incorporated into the biofilms survived the stress of dessication much better than did planktonic bacteria, with over a 400-fold increase in survival in the biofilm-bound bacteria. SOS-inducing drugs also triggered DNA release in Proteus mirabilis, with ssDNA again being more abundant than dsDNA in the culture supernatants. Addition of urea in this urease-producing organism triggered the formation of struvite crystals (magnesium ammonium phosphate), with the crystals, Proteus bacteria, and extracellular DNA forming mixed biofilms. Last, we tested the effect of inhibitors of the SOS response, such as zinc acetate. We also tested an inhibitor of the generalized stress response, dequalinium, which also indirectly inhibits the SOS response, and found it had a strong ability to inhibit biofilm formation.

Cranberry constituents prevent SOS-mediated filamentation of uropathogenic Escherichia coli

The diameter, length, and shape of bacteria are maintained with such high fidelity that these parameters are classically used as metrics in the distinction of bacterial species. Increasing evidence indicates that bacteria transiently shift their shapes into distinctive morphologies in response to environmental changes. Elongation of bacterial length into a filamentous shape provides unique survival advantages for many bacterial species. Analysis of 42 clinical isolates of uropathogenic Escherichia coli (UPEC) revealed that filamentation to host-derived antimicrobials is a conserved phenotype. Therefore, we hypothesize that filamentation represents a conserved mechanism of pathogenic bacterial persistence that can be targeted for narrow-spectrum, anti-virulence therapies. We demonstrate that cranberries prevent SulA-mediated filamentation of UPEC. Furthermore, we identify multiple fractions of cranberries that retain anti-filamentation properties. These studies provide mechanistic insight into the clinical efficacy of cranberry for patients with recurrent urinary tract infections. Inhibition of filamentation represents a novel approach to promote bacterial pathogen susceptibility to immune and antibiotic-mediated clearance to attenuate disease.

Confounder or Confederate? The Interactions Between Drugs and the Gut Microbiome in Psychiatric and Neurological Diseases

The gut microbiome is emerging as an important factor in signaling along the gut-brain axis. The intimate physiological connection between the gut and the brain allows perturbations in the microbiome to be directly transmitted to the central nervous system and thereby contribute to psychiatric and neurological diseases. Common microbiome perturbations result from the ingestion of xenobiotic compounds including pharmaceuticals such as psychotropic drugs. In recent years, a variety of interactions between these drug classes and the gut microbiome have been reported, ranging from direct inhibitory effects on gut bacteria to microbiome-mediated drug degradation or sequestration. Consequently, the microbiome may play a critical role in influencing the intensity, duration, and onset of therapeutic effects, as well as in influencing the side effects that patients may experience. Furthermore, because the composition of the microbiome varies from person to person, the microbiome may contribute to the frequently observed interpersonal differences in the response to these drugs. In this review, we first summarize the known interactions between xenobiotics and the gut microbiome. Then, for psychopharmaceuticals, we address the question of whether these interactions with gut bacteria are irrelevant for the host (i.e., merely confounding factors in metagenomic analyses) or whether they may even have therapeutic or adverse effects.

Role of Extracellular DNA in Bacterial Response to SOS-Inducing Drugs

The SOS response is a conserved stress response pathway that is triggered by DNA damage in the bacterial cell. Activation of this pathway can, in turn, cause the rapid appearance of new mutations, sometimes called hypermutation. We compared the ability of various SOS-inducing drugs to trigger the expression of RecA, cause hypermutation, and produce elongation of bacteria. During this study, we discovered that these SOS phenotypes were accompanied by the release of large amounts of DNA into the extracellular medium. The release of DNA was accompanied by a form of bacterial aggregation in which the bacteria became tightly enmeshed in DNA. We hypothesize that DNA release triggered by SOS-inducing drugs could promote the horizontal transfer of antibiotic resistance genes by transformation or by conjugation.

Repurposing Antidepressants and Phenothiazine Antipsychotics as Efflux Pump Inhibitors in Cancer and Infectious Diseases

Multidrug resistance (MDR) is a major obstacle in the therapy of infectious diseases and cancer. One of the major mechanisms of MDR is the overexpression of efflux pumps (EPs) that are responsible for extruding antimicrobial and anticancer agents. EPs have additional roles of detoxification that may aid the development of bacterial infection and the progression of cancer. Therefore, targeting EPs may be an attractive strategy to treat bacterial infections and cancer. The development and discovery of a new drug require a long timeline and may come with high development costs. A potential alternative to reduce the time and costs of drug development is to repurpose already existing drugs. Antidepressants and antipsychotic agents are widely used in clinical practice in the treatment of psychiatric disorders and some somatic diseases. Antidepressants and antipsychotics have demonstrated various beneficial activities that may be utilized in the treatment of infections and cancer. This review aims to provide a brief overview of antibacterial and anticancer effects of selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs) and phenothiazine antipsychotics, while focusing on EPs. However, it should be noted that the antimicrobial activity of a traditionally non-antibiotic drug may have clinical implications regarding dysbiosis and bacterial MDR.

Defects in DNA double-strand break repair resensitize antibiotic-resistant Escherichia coli to multiple bactericidal antibiotics

Antibiotic resistance is becoming increasingly prevalent amongst bacterial pathogens and there is an urgent need to develop new types of antibiotics with novel modes of action. One promising strategy is to develop resistance-breaker compounds, which inhibit resistance mechanisms and thus resensitize bacteria to existing antibiotics. In the current study, we identify bacterial DNA double-strand break repair as a promising target for the development of resistance-breaking co-therapies. We examined genetic variants of Escherichia coli that combined antibiotic-resistance determinants with DNA repair defects. We observed that defects in the double-strand break repair pathway led to significant resensitization toward five bactericidal antibiotics representing different functional classes. Effects ranged from partial to full resensitization. For ciprofloxacin and nitrofurantoin, sensitization manifested as a reduction in the minimum inhibitory concentration. For kanamycin and trimethoprim, sensitivity manifested through increased rates of killing at high antibiotic concentrations. For ampicillin, repair defects dramatically reduced antibiotic tolerance. Ciprofloxacin, nitrofurantoin, and trimethoprim induce the promutagenic SOS response. Disruption of double-strand break repair strongly dampened the induction of SOS by these antibiotics. Our findings suggest that if break-repair inhibitors can be developed they could resensitize antibiotic-resistant bacteria to multiple classes of existing antibiotics and may suppress the development of de novo antibiotic-resistance mutations.

Inhibition of SOS Response by Nitric Oxide Donors in Escherichia coli Blocks Toxin Production and Hypermutation

Background

Previous reports have differed as to whether nitric oxide inhibits or stimulates the SOS response, a bacterial stress response that is often triggered by DNA damage. The SOS response is an important regulator of production of Shiga toxins (Stx) in Shiga-toxigenic E. coli (STEC). In addition, the SOS response is accompanied by hypermutation, which can lead to de novo emergence of antibiotic resistance. We studied these effects in vitro as well as in vivo.

Results

Nitric oxide donors inhibited induction of the SOS response by classical inducers such as mitomycin C, ciprofloxacin, and zidovudine, as measured by assays for E. coli RecA. Nitric oxide donors also inhibited Stx toxin protein production as well as stx2 RNA in vitro and in vivo. In vivo experiments were performed with ligated ileal segments in the rabbit using a 20 h infection. The NO donor S-nitroso-acetylpenicillamine (SNAP) reduced hypermutation in vitro and in vivo, as measured by emergence of rifampin resistance. SNAP blocked the ability of the RecA protein to bind to single-stranded DNA in an electrophoretic mobility shift assay (EMSA) in vitro, an early event in the SOS response. The inhibitory effects of SNAP were additive with those of zinc acetate.

Conclusions

Nitric oxide donors blocked the initiation step of the SOS response. Downstream effects of this blockade included inhibition of Stx production and of hypermutation. Infection of rabbit loops with STEC resulted in a downregulation, rather than stimulation, of nitric oxide host defenses at 20 h of infection.