Three supplementary methods for analyzing cytotoxicity of Escherichia coli O157:H7

Dendrobium officinale polysaccharides attenuate uropathogenic Escherichia coli (UPEC)-induced pyroptosis in macrophage cells

Urinary tract infections (UTI) are recognized as one of the most common infectious diseases worldwide, and uropathogenic Escherichia coli (UPEC) is the main causative agent of UTI. Dendrobium officinale polysaccharides (DOPs), the main effective ingredient in Dendrobium officinale, have been reported to possess an anti-inflammatory role. Whether DOPs can attenuate the inflammatory injury (pyroptosis) induced by UPEC remains unknown. The present study aimed to assess the protective effect and potential mechanism of DOPs in UPEC-induced pyroptosis. Cell viability of THP-1 differentiated macrophage cells with DOPs was determined using MTT assay. Pyroptosis by UPEC in macrophage cells with or not DOPs pre-treatment was evaluated with flow cytometry analysis, lactate dehydrogenase (LDH) assay, and proinflammatory cytokines secretion. Expression level of key proteins in the NLRP3/Caspase-1/GSDMD pyroptotic pathway was analyzed with western blot. Furthermore the effect of DOPs on ROS activation was investigated. Results indicated that DOPs attenuated UPEC-induced cell damage in macrophage cells, inhibited the activation of NLRP3 mediated inflammasome, subsequently decreased induction and activation of caspase-1/GSDMD, and reduced the secretion of pro-inflammatory cytokine (IL-1β et al.). Moreover, pretreatment with DOPs significantly reduces ROS production, an important/putative pyroptosis stimulus signal. These results suggested that DOPs successfully mitigate UPEC-promoted pyroptosis in macrophage cells. The protective effects of DOPs are associated with the inhibition of the NLRP3/Caspase-1/GSDMD pathway and ROS signal activation.

A previously uncharacterized two-component signaling system in uropathogenic Escherichia coli coordinates protection against host-derived oxidative stress with activation of hemolysin-mediated host cell pyroptosis

Uropathogenic Escherichia coli (UPEC) deploy an array of virulence factors to successfully establish urinary tract infections. Hemolysin is a pore-forming toxin, and its expression correlates with the severity of UPEC infection. Two-component signaling systems (TCSs) are a major mechanism by which bacteria sense environmental cues and respond by initiating adaptive responses. Here, we began this study by characterizing a novel TCS (C3564/C3565, herein renamed orhK/orhR for oxidative resistance and hemolysis kinase/regulator) that is encoded on a UPEC pathogenicity island, using bioinformatic and biochemical approaches. A prevalence analysis indicates that orhK/orhR is highly associated with the UPEC pathotype, and it rarely occurs in other E. coli pathotypes tested. We then demonstrated that OrhK/OrhR directly activates the expression of a putative methionine sulfoxide reductase system (C3566/C3567) and hemolysin (HlyA) in response to host-derived hydrogen peroxide (H₂O₂) exposure. OrhK/OrhR increases UPEC resistance to H₂O₂in vitro and survival in macrophages in cell culture via C3566/C3567. Additionally, OrhK/OrhR mediates hemolysin-induced renal epithelial cell and macrophage death via a pyroptosis pathway. Reducing intracellular H₂O₂ production by a chemical inhibitor impaired OrhK/OrhR-mediated activation of c3566-c3567 and hlyA. We also uncovered that UPEC links the two key virulence traits by cotranscribing the c3566-c3567 and hlyCABD operons. Taken together, our data suggest a paradigm in which a signal transduction system coordinates both bacterial pathogen defensive and offensive traits in the presence of host-derived signals; and this exquisite mechanism likely contributes to hemolysin-induced severe pathological outcomes.

Uropathogenic Escherichia coli (UPEC) is the primary cause of urinary tract infections, and approximately half of UPEC isolates produce a pore-forming toxin, hemolysin. Clinically, hemolysin carriage is associated with severe pathology and symptoms during UPEC infections. However, overexpression of hemolysin can be detrimental to UPEC colonization. Therefore, fine-tuning of hemolysin expression in response to in vivo-relevant signals is critical for optimal UPEC fitness in the urinary tract. In this study, we describe a virulence strategy employed by UPEC, i.e., the bacteria use a two-component signaling (TCS) system to coordinate oxidative stress resistance and hemolysin-mediated pyroptosis of host cells in response to host-derived oxidative signals. The TCS achieves this coordination by cotranscribing genes encoding the oxidative stress resistance and the hemolysin. As a result, UPEC is able to link defense to offense, and this exquisite virulence mechanism likely contributes to UPEC fitness in vivo and hemolysin-induced severe pathological outcomes.

From hazard analysis to risk control using rapid methods in microbiology: A practical approach for the food industry

The prevention of foodborne diseases is one of the main objectives of health authorities. To this effect, analytical techniques to detect and/or quantify the microbiological contamination of foods prior to their release onto the market are required. Management and control of foodborne pathogens have generally been based on conventional detection methodologies, which are not only time-consuming and labor-intensive but also involve high consumable materials costs. However, this management perspective has changed over time given that the food industry requires efficient analytical methods that obtain rapid results. This review covers the historical context of traditional methods and their passage in time through to the latest developments in rapid methods and their implementation in the food sector. Improvements and limitations in the detection of the most relevant pathogens are discussed from a perspective applicable to the current situation in the food industry. Considering efforts that are being done and recent developments, rapid and accurate methods already used in the food industry will be also affordable and portable and offer connectivity in near future, which improves decision-making and safety throughout the food chain.

Rapid and accurate detection of Escherichia coli O157:H7 in beef using microfluidic wax-printed paper-based ELISA

Escherichia coli O157:H7 is a severe foodborne pathogen. Paper-based ELISA can rapidly and accurately detect E.coli O157:H7 in beef. The method has good sensitivity, specificity and repeatability. It is suitable for point-of-care testing and offers new ideas for the detection of other foodborne pathogens.

Validation and verification of LAMP, ISO, and VIDAS UP methods for detection of Escherichia coli O157:H7 in different food matrices

Escherichia coli O157:H7 is one of the most important food-borne pathogens to threaten public health. Cultural methods are used as a gold standard while they are laborious and time-consuming. Loop-mediated isothermal amplification (LAMP) method is an alternative method that became widely used for the detection of food-borne pathogens. The aim of this study was to evaluate the specificity and sensitivity of LAMP method for detection of E. coli O157:H7, also to compare detection performances with VIDAS UP and ISO (International Organization for Standardization) methods in different food matrices (beef meat, minced lamb meat, milk, cheese, apple puree, and soybean sprouts). E. coli O157:H7 were spiked in three different levels (high 4.58; medium 2.32; low 0.30 log₁₀ CFU/g-ml) to food matrices. Although there were no significant differences in terms of the specificity and sensitivity values among the three methods (p ≥ .05), it was determined that the highest specificity and sensitivity values obtained from the LAMP method. Sensitivity and specificity values of LAMP method were found as 0.997 and 0.988, for the ISO method were 0.989 and 0.971, and for the VIDAS UP method were 0.980 and 0.963, respectively. In milk samples, sensitivity and specificity values of the VIDAS UP method were significantly lower than LAMP and ISO methods (p < .05). However, there were no significant differences found for the other food matrices among the three methods (p > .05). It can be summarized from this study that specificity and sensitivity values of the LAMP method are equal or higher and less time-consuming than ISO and VIDAS UP methods. In conclusion, using a simple, fast, and inexpensive detection method, such as LAMP, especially in endemic regions or in an outbreak to control spreading of pathogens, is very important for public health.

Antibacterial Properties of Tebipenem Pivoxil Tablet, a New Oral Carbapenem Preparation against a Variety of Pathogenic Bacteria in Vitro and in Vivo

Aims: To systemically investigate the in vitro and in vivo antibacterial properties of tebipenem pivoxil tablet. In addition, acute toxicity of this preparation was also studied. Methods: In vitro, minimum inhibitory concentration (MIC) or minimal inhibitory concentration (MBC) were determined by using the serial 2-fold broth or agar dilution methods. Further, cumulative MIC inhibition curves were then made to assess the antibacterial effects of the drug at various concentrations. In vivo, minimum lethal dose (MLD) in combination with maximum tolerance dose (MTD) was used to measure the acute toxicity of the tebipenem pivoxil tablet in mice. After that, sepsis mouse models challenged with Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, respectively, were established to evaluate the anti-infective effect of this preparation. Results: The MIC₉₀ values of tebipenem pivoxil against Gram-positive bacteria such as methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), methicillin-sensitive Staphylococcus epidermidis (MSSE), methicillin-resistant Staphylococcus epidermidis (MRSE), Pyogenic streptococcus, and Enterococcus faecalis were ≤0.125, 16, 0.5, 8, ≤0.125, and 32 μg/mL, respectively. Correspondingly, the MIC₉₀ values of tebipenem pivoxil against Escherichia coli, Klebsiellapneumoniae, Enterobacter aerogenes, Haemophilus influenzae, Pseudomonas aeruginosa, and Acinetobacter baumannii were 1, 0.5, ≤0.125, 0.25, 64, 64 μg/mL, respectively. The MBC values of tebipenem pivoxil against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae were 0.016–2, 0.063–32, 0.031–32 μg/mL, respectively. The acute toxicity study showed that the MLD of the tebipenem pivoxil tablet was 4.00 g/kg and the MTD was 3.40 g/kg in mice. In all the sepsis mouse models, the simultaneous administration of the tebipenem pivoxil tablets significantly reduced mortality of the sepsis-model mice as compared with the control. Furthermore, the survival rate in the tebipenem pivoxil tablet group was remarkably higher than that in the meropenem group in all the sepsis mouse models tested. In the sepsis model challenged with Staphylococcus aureus ATCC29213, Escherichia coli ATCC25922, Pseudomonas aeruginosa ATCC27853, and Pseudomonas aeruginosa clinical strain, respectively, tebipenem pivoxil tablet (100 mg/kg) displayed a better protective effect than tebipenem pivoxil granules (100 mg/kg). Conclusions: In summary, tebipenem pivoxil displays an excellent antibacterial activity against a variety of pathogenic bacteria in vitro. Importantly, tebipenem pivoxil tablet significantly protects the sepsis mice challenged with various pathogenic bacteria, which may provide a potential approach to treating bacterial sepsis in clinic.