Effect of antibiotics on cellular stress generated in Shiga toxin-producing Escherichia coli O157:H7 and non-O157 biofilms

The action of phytochemicals in biofilm control

Covering: 2009 to 2021Antimicrobial resistance is now rising to dangerously high levels in all parts of the world, threatening the treatment of an ever-increasing range of infectious diseases. This has becoming a serious public health problem, especially due to the emergence of multidrug-resistance among clinically important bacterial species and their ability to form biofilms. In addition, current anti-infective therapies have low efficacy in the treatment of biofilm-related infections, leading to recurrence, chronicity, and increased morbidity and mortality. Therefore, it is necessary to search for innovative strategies/antibacterial agents capable of overcoming the limitations of conventional antibiotics. Natural compounds, in particular those obtained from plants, have been exhibiting promising properties in this field. Plant secondary metabolites (phytochemicals) can act as antibiofilm agents through different mechanisms of action from the available antibiotics (inhibition of quorum-sensing, motility, adhesion, and reactive oxygen species production, among others). The combination of different phytochemicals and antibiotics have revealed synergistic or additive effects in biofilm control. This review aims to bring together the most relevant reports on the antibiofilm properties of phytochemicals, as well as insights into their structure and mechanistic action against bacterial pathogens, spanning December 2008 to December 2021.

Synergistic Effects of Bacteriophage vB_Eco4-M7 and Selected Antibiotics on the Biofilm Formed by Shiga Toxin-Producing Escherichia coli

Apart from antibiotic resistance of pathogenic bacteria, the formation of biofilms is a feature that makes bacterial infections especially difficulty to treat. Shiga toxin-producing Escherichia coli (STEC) strains are dangerous pathogens, causing severe infections in humans, and capable of biofilm production. We have reported previously the identification and characterization of the vB_Eco4-M7 bacteriophage, infecting various STEC strains. It was suggested that this phage might be potentially used in phage therapy against these bacteria. Here, we tested the effects of vB_Eco4-M7 alone or in a phage cocktail with another STEC-infecting phage, and/or in a combination with different antibiotics (ciprofloxacin and rifampicin) on biofilm formed by a model STEC strain, named E. coli O157:H7 (ST2-8624). The vB_Eco4-M7 phage appeared effective in anti-biofilm action in all these experimental conditions (2–3-fold reduction of the biofilm density, and 2–3 orders of magnitude reduction of the number of bacterial cells). However, the highest efficiency in reducing a biofilm’s density and number of bacterial cells was observed when phage infection preceded antibiotic treatment (6-fold reduction of the biofilm density, and 5–6 orders of magnitude reduction of the number of bacterial cells). Previous reports indicated that the use of antibiotics to treat STEC-caused infections might be dangerous due to the induction of Shiga toxin-converting prophages from bacterial genomes under stress conditions caused by antibacterial agents. We found that ciprofloxacin was almost as efficient in inducing prophages from the E. coli O15:H7 (ST2-8624) genome as a classical inducer, mitomycin C, while no detectable prophage induction could be observed in rifampicin-treated STEC cells. Therefore, we conclude the latter antibiotic or similarly acting compounds might be candidate(s) as effective and safe drug(s) when used in combination with phage therapy to combat STEC-mediated infections.

Host-pathogen interaction between macrophage co-cultures with Staphylococcus aureus biofilms

The ability of Staphylococcus aureus to form biofilms is an important virulence factor. During the infectious process, the interaction between biofilms and immune cells is determinant; however, the properties that make biofilms resistant to the immune system are not well characterized. In order to better understand this, we evaluated the in vitro interaction of macrophages during the early stages of S. aureus biofilm formation. Biofilm formation was evaluated by crystal violet staining, light microscopy, and confocal scanning laser microscopy. Furthermore, different activation on L-arginine pathways such as nitric oxide (NO^•) release and the arginase, the production of reactive oxygen species (ROS), the total oxidative stress response (OSR), and levels of cytokine liberation, were determined. Our findings show that the interaction between biofilms and macrophages results in stimuli for catabolism of L-arginine via arginase, but not for NO^•, an increase of ROS production, and activation of the non-enzymatic OSR. We also observed the production of IL-6, but not of TNFα o IL-10 in these co-cultures. These results contribute to a better understanding of host-pathogen interactions and suggest that biofilms increase resistance against immune cell mechanisms, a phenomenon that could contribute to the ability of S. aureus biofilms to establish mature biofilms.

Paeoniflorin Derivative in Paeoniae Radix Aqueous Extract Suppresses Alpha-Toxin of Staphylococcus aureus

The emergence and dissemination of bacterial infections is paralyzing our public health systems worldwide. Worse still, there are no effective antibiotics against bacterial toxins, which facilitate the infection. Natural herbs that target bacterial toxins may be a better choice for therapy of infectious diseases. However, most natural drugs present unknown compositions and unclear mechanisms. Here we demonstrated that the Chinese herb Paeoniae Radix aqueous extract (PRAE) could suppress alpha-toxin (α-toxin) of Staphylococcus aureus. We observed that the paeoniflorin derivative (PRAE-a) derivative in PRAE significantly abolished the hemolytic activity of S. aureus α-toxin. The analyses of high-performance liquid chromatography (HPLC), mass spectrometer (MS), Fourier transform infrared spectrometer (FTIR), and nuclear magnetic resonance (NMR) showed that PRAE-a was a glycoside compound with a paeoniflorin nucleus. We further found that PRAE-a disrupted the pore-forming ability of α-toxin by prevention of the dimer to heptamer. Therefore, PRAE-a proved to be an effective therapy for S. aureus lung infections in mice by inhibiting α-toxin. Collectively, these results highlighted that PRAE-a can be used as an antibacterial agent to attenuate S. aureus virulence by targeting α-toxin.

A pediatric neurologic assessment score may drive the eculizumab-based treatment of Escherichia coli-related hemolytic uremic syndrome with neurological involvement

BACKGROUND

Thrombotic microangiopathy (TMA) is a clinical syndrome encompassing a large group of rare but severe disorders including thrombotic thrombocytopenic purpura (TTP) and both typical and atypical forms of hemolytic uremic syndrome (HUS). The key role of the complement system is well known in TTP and atypical HUS, but recent reports describe its involvement in the pathogenesis of HUS secondary to gastrointestinal infections due to Shiga toxin-producing Escherichia coli (STEC).

METHODS

TMA mainly affects the kidney, but extra-renal complications are frequently described. The involvement of the central nervous system (CNS) represents often a life-threatening condition and it can result in serious long-term disability in HUS patients who overcome the acute phase of illness. In the present study, we retrospectively analyzed a pediatric cohort of a single tertiary pediatric hospital in Southern Italy, in which this complication occurred in 12/54 children (22% of cases), of whom five with severe neurological involvement had been successfully treated with eculizumab.

RESULTS

The great clinical variability of brain injury in our cohort has led us to retrospectively build a "neurological score" useful to assess the clinical severity of neurologic involvement. Subjects with higher neurologic score due to the most severe CNS involvement resulted in the group of patients early treated with eculizumab, obtaining a good clinical response (four out five patients). In conclusion, the early treatment with eculizumab in children with severe neurological involvement during STEC-HUS was associated with complete regression of both acute kidney injury (AKI) and neurological lesions observed at magnetic resonance imaging (MRI).

CONCLUSIONS

A "neurological score" may be a useful tool to drive the early treatment of CNS complications in STEC-HUS with eculizumab, although future perspective controlled studies are urgently needed to validate this therapeutic approach.

Antibacterial Efficacy of Silver Nanoparticles on Endometritis Caused by Prevotella melaninogenica and Arcanobacterum pyogenes in Dairy Cattle

Bovine postpartum diseases remain one of the most significant and highly prevalent illnesses with negative effects on the productivity, survival, and welfare of dairy cows. Antibiotics are generally considered beneficial in the treatment of endometritis; however, frequent usage of each antibiotic drug is reason for the emergence of multidrug resistance (MDR) of the pathogenic microorganisms, representing a major impediment for the successful diagnosis and management of infectious diseases in both humans and animals. We synthesized silver nanoparticles (AgNPs) with an average size of 10 nm using the novel biomolecule apigenin as a reducing and stabilizing agent, and evaluated the efficacy of the AgNPs on the MDR pathogenic bacteria Prevotella melaninogenica and Arcanobacterium pyogenes isolated from uterine secretion samples. AgNPs inhibited cell viability and biofilm formation in a dose- and time-dependent manner. Moreover, the metabolic toxicity of the AgNPs was assessed through various cellular assays. The major toxic effect of cell death was caused by an increase in oxidative stress, as evidenced by the increased generation of reactive oxygen species (ROS), malondialdehyde, protein carbonyl content, and nitric oxide. The formation of ROS is considered to be the primary mechanism of bacterial death. Therefore, the biomolecule-mediated synthesis of AgNPs shows potential as an alternative antimicrobial therapy for bovine metritis and endometritis.

On the mechanism of Candida tropicalis biofilm reduction by the combined action of naturally-occurring anthraquinones and blue light

The photoprocesses involved in the photo-induced Candida tropicalis biofilm reduction by two natural anthraquinones (AQs), rubiadin (1) and rubiadin-1-methyl ether (2), were examined. Production of singlet oxygen (¹O₂) and of superoxide radical anion (O₂^•−) was studied. Although it was not possible to detect the triplet state absorption of any AQs in biofilms, observation of ¹O₂ phosphorescence incubated with deuterated Phosphate Buffer Solution, indicated that this species is actually formed in biofilms. 2 was accumulated in the biofilm to a greater extent than 1 and produced measurable amounts of O₂^•− after 3h incubation in biofilms. The effect of reactive oxygen species scavengers on the photo-induced biofilm reduction showed that Tiron (a specific O₂^•− scavenger) is most effective than sodium azide (a specific ¹O₂ quencher). This suggests that O₂^•− formed by electron transfer quenching of the AQs excited states, is the main photosensitizing mechanism involved in the photo-induced antibiofilm activity, whereas ¹O₂ participation seems of lesser importance.

Intra- and Extracellular Biosynthesis and Characterization of Iron Nanoparticles from Prokaryotic Microorganisms with Anticoagulant Activity

BACKGROUND

The use of microorganisms for the synthesis of nanoparticles (NPs) is relatively new in basic research and technology areas.

PURPOSE

This work was conducted to optimized the biosynthesis of iron NPs intra- and extracellular by Escherichia coli or Pseudomonas aeruginosa and to evaluate their anticoagulant activity.

STUDY DESIGN/METHODS

The structures and properties of the iron NPs were investigated by Ultraviolet-visible (UV-vis) spectroscopy, Zeta potential, Dynamic light scattering (DLS), Field emission scanning electron microscope (FESEM)/ Energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). Anticoagulant activity was determined by conducting trials of Thrombin Time (TT), Activated Partial Prothrombin Time (APTT) and Prothrombin Time (PT).

RESULTS

UV-vis spectrum of the aqueous medium containing iron NPs showed a peak at 275 nm. The forming of iron NPs was confirmed by FESEM/ EDX, and TEM. The morphology was spherical shapes mostly with low polydispersity and the average particle diameter was 23 ± 1 nm. Iron NPs showed anticoagulant activity by the activation of extrinsic pathway.

CONCLUSION

The eco-friendly process of biosynthesis of iron NPs employing prokaryotic microorganisms presents a good anticoagulant activity. This could be explored as promising candidates for a variety of biomedical and pharmaceutical applications.

The anthraquinones rubiadin and its 1-methyl ether isolated from Heterophyllaea pustulata reduces Candida tropicalis biofilms formation

BACKGROUND

Candida tropicalis is increasingly becoming among the most commonly isolated pathogens causing fungal infections with an important biofilm-forming capacity.

PURPOSE

This study addresses the antifungal effect of rubiadin (AQ1) and rubiadin 1-methyl ether (AQ2), two photosensitizing anthraquinones (AQs) isolated from Heterophyllaea pustulata, against C. tropicalis biofilms, by studying the cellular stress and antioxidant response in two experimental conditions: darkness and irradiation. The combination with Amphotericin B (AmB) was assayed to evaluate the synergic effect.

STUDY DESIGN/METHODS

Biofilms of clinical isolates and reference strain of Candida tropicalis were treated with AQs (AQ1 or AQ2) and/or AmB, and the biofilms depletion was studied by crystal violet and confocal scanning laser microscopy (CSLM). The oxidant metabolites production and the response of antioxidant defense system were also evaluated under dark and irradiation conditions, being the light a trigger for photo-activation of the AQs. The Reactive Oxygen Species (ROS) were detected by the reduction of Nitro Blue Tetrazolium test, and Reactive Nitrogen Intermediates (RNI) by the Griess assay. ROS accumulation was also detected inside biofilms by using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) probe, which was visualized by CSLM. Superoxide dismutase (SOD) activity and the total antioxidant capacity of biofilms were measured by spectrophotometric methods. The minimun inhibitory concentration for sessile cells (SMIC) was determined for each AQs and AmB. The fractional inhibitory concentration index (FICI) was calculated for the combinations of each AQ with AmB by the checkerboard microdilution method.

RESULTS

Biofilm reduction of both strains was more effective with AQ1 than with AQ2. The antifungal effect was mediated by an oxidative and nitrosative stress under irradiation, with a significant accumulation of endogenous ROS detected by CSLM and an increase in the SOD activity. Thus, the prooxidant-antioxidant balance was altered especially by AQ1. The best synergic combination with AmB was also obtained with AQ1 (80.5%) (FICI=0.74).

CONCLUSION

Under irradiation, the oxidative stress was the predominant effect, altering the prooxidant-antioxidant balance, which may be the cause of the irreversible cell injury in the biofilm. Our results showed synergism of these natural AQs with AmB. Therefore, the photosensitizing AQ1 could be an alternative for the Candida infections treatment, which deserves further investigation.

Oxidative stress generation of silver nanoparticles in three bacterial genera and its relationship with the antimicrobial activity

Oxidative stress is a condition caused by the high intracellular concentrations of reactive oxygen species (ROS) that includes superoxide anion radicals, hydroxyl radicals and hydrogen peroxide. Nanoparticles could cause rapid generation of free radicals by redox reactions. ROS can react directly with membrane lipids, proteins and DNA and are normally scavenged by antioxidants that are capable of neutralizing; however, elevated concentrations of ROS in bacterial cells can result in oxidative stress. The aim of this work was contribute to the knowledge of action mechanism of silver nanoparticles (Ag-NPs) and their relation to the generation of oxidative stress in bacteria. We demonstrated that Ag-NPs generated oxidative stress in Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa mediated by the increment of ROS and this increase correlated with a better antimicrobial activity. On the other hand, we showed that the oxidative stress caused by the Ag-NPs biosynthesized was associated to a variation in the level of reactive nitrogen intermediates (RNI). Oxidative stress in bacteria can result from disruption of the electronic transport chain due to the high affinity of Ag-NPs for the cell membrane. This imbalance in the oxidative stress was evidentiated by a macromolecular oxidation at level of DNA, lipids and proteins in E. coli exposed to Ag-NPs. The formation of ROS and RNI by Ag-NPs may also be considered to explain the bacterial death.

Shiga toxins: from structure and mechanism to applications

Shiga toxins are a group of type 2 ribosome-inactivating proteins (RIPs) produced in several types of bacteria. The toxins possess an AB5 structure, which comprises a catalytic A chain with N-glycosidase activity, and five identical B chains and recognize and bind to the target cells with specific carbohydrate moieties. In humans, the major molecular target which recognizes the Shiga toxins is the Gb3 receptor, which is mainly expressed on the cell surface of endothelial cells of the intestine, kidney, and the brain. This causes these organs to be susceptible to the toxicity of Shiga toxins. When a person is infected by Shiga toxin-producing bacteria, the toxin is produced in the gut, translocated to the circulatory system, and carried to the target cells. Toxicity of the toxin causes inflammatory responses and severe cell damages in the intestine, kidneys, and brain, bringing about the hemolytic uremic syndrome (HUS), which can be fatal. The Shiga toxin requires a couple of steps to exert its toxicity to the target cells. After binding with the target cell surface receptor, the toxin requires a complicated process to be transported into the cytosol of the cell before it can approach the ribosomes. The mechanisms for the interactions of the toxin with the cells are described in this review. The consequences of the toxin on the cells are also discussed. It gives an overview of the steps for the toxin to be produced and transported, expression of catalytic activity, and the effects of the toxin on the target cells, as well as effects on the human body.