Phenolic acids potentiate colistin-mediated killing of Acinetobacter baumannii by inducing redox imbalance

Can flow cytometric measurements of reactive oxygen species levels determine minimal inhibitory concentrations and antibiotic susceptibility testing for Acinetobacter baumannii?

Current antimicrobial susceptibility testing (AST) requires 16-24 hours, delaying initiation of appropriate antibiotics. Hence, there is a need for rapid AST. This study aims to develop and evaluate the feasibility of a rapid flow cytometric AST assay to determine minimum inhibitory concentration (MIC) for carbapenem-resistant Acinetobacter baumannii (CRAB). Antibiotic exposure causes increased intracellular reactive oxygen species (ROS) in bacteria. We hypothesized that ROS can be used as a marker to determine MIC. We assessed three CRAB clinical isolates across fifteen antibiotics at various concentrations in a customized 96-well microtiter plate. The antibiotics assessed include amikacin, beta-lactams (ampicillin/sulbactam, aztreonam, cefepime, ceftolozane/tazobactam, doripenem, imipenem, meropenem, and piperacillin/tazobactam), levofloxacin, polymyxin B, rifampicin, trimethoprim/sulfamethoxazole, and tetracyclines (tigecycline and minocycline). These clinical CRAB isolates were assessed for ROS after antibiotic treatment. Increased ROS levels indicated by increased RedoxSensorTM Green (RSG) fluorescence intensity was assessed using flow cytometry (FCM). MIC was set as the lowest antibiotic concentration that gives a ≥1.5-fold increase in mode RSG fluorescence intensity (MICRSG). Accuracy of MICRSG was determined by comparing against microtiter broth dilution method performed under CLSI guidelines. ROS was deemed accurate in determining the MICs for β-lactams (83.3% accuracy) and trimethoprim/sulfamethoxazole (100% accuracy). In contrast, ROS is less accurate in determining MICs for levofloxacin (33.3% accuracy), rifampicin (0% accuracy), amikacin (33.3% accuracy), and tetracyclines (33.3% accuracy). Collectively, this study described an FCM-AST assay to determine antibiotic susceptibility of CRAB isolates within 5 hours, reducing turnaround time up to 19 hours.

Investigating the anti-growth, anti-resistance, and anti-virulence activities of Schoepfia schreberi J.F.Gmel. against the superbug Acinetobacter baumannii

Schoepfia schreberi has been used in Mayan folk medicine to treat diarrhea and cough. This study aimed to determine the anti-growth, anti-resistance, and/or anti-virulence activities of S. schreberi extracts against Acinetobacter baumannii, a pathogen leader that causes healthcare-associated infections with high rates of drug-resistant including carbapenems, the last line of antibiotics known as superbugs, and analyze their composition using HPLC-DAD. Ethyl acetate (SSB-3) and methanol (SSB-4) bark extracts exhibit antimicrobial and biocidal effects against drug-susceptible and drug-resistant A. baumannii. Chemical analysis revealed that SSB-3 and SSB-4 contained of gallic and ellagic acids derivatives. The anti-resistance activity of the extracts revealed that SSB-3 or SSB-4, combined with imipenem, exhibited potent antibiotic reversal activity against A. baumannii by acting as pump efflux modulators. The extracts also displayed activity against surface motility of A. baumannii and its capacity to survive reactive oxygen species. This study suggests that S. schreberi can be considered a source of antibiotics, even adjuvanted compounds, as anti-resistant or anti-virulence agents against A. baumannii, contributing to ethnopharmacological knowledge and reappraisal of Mayan medicinal flora, and supporting the traditional use of the bark of the medicinal plant S. schreberi for the treatment of infectious diseases.

Treatment of subclinical mastitis in dairy goats experimentally infected with Staphylococcus aureus using natural therapeutic protocol

In herds of dairy goats, mastitis represents a major health and economic problem due to the multiresistance of some microorganisms. In this context, the study aimed to determine the potential of antimicrobial action and antibiofilm of the crude ethanolic extract (CEE) of Hymenaea martiana (jatobá) leaves, as well its fractions, on Staphylococcus sp isolated from bacterial cultures of goat milk. In vitro assays were performed to determine the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC), as well as tests of the effect of CEE on biofilm formation and quantification and the consolidated biofilm. The experimental infection was performed in two groups, each consisting of five goat. Experimental Group 1 (G1) consisted of five females treated with an intramammary ointment based on the CEE, at a concentration of 5%. Experimental Group 2 (G2) consisted of five females treated with a commercial intramammary ointment based on gentamicin, once a day, for six consecutive days. The diagnosis of mastitis was performed using a bacterial culture. The dichloromethane fraction of CEE was the one with the lowest concentrations of MBC, ranging from 195.3 to 781 µg / ml. Concerning to the biofilm, interference of the tested extract was observed for two isolates. In the present study, the ointment prepared from H. martiana extract (jatobá) was able to reduce bacterial infection in mammary glands experimentally infected with S. aureus. Antibacterial activity may be related to the classes of secondary metabolites found.

Evidence on the inhibitory effect of Brassica plants against Acinetobacter baumannii lipases: phytochemical analysis, in vitro, and molecular docking studies

BACKGROUND

Infections caused by Acinetobacter baumannii are becoming a rising public health problem due to its high degree of acquired and intrinsic resistance mechanisms. Bacterial lipases penetrate and damage host tissues, resulting in multiple infections. Because there are very few effective inhibitors of bacterial lipases, new alternatives for treating A. baumannii infections are urgently needed. In recent years, Brassica vegetables have received a lot of attention since their phytochemical compounds have been directly linked to diverse antimicrobial actions by inhibiting the growth of various Gram-positive and Gram-negative bacteria, yeast, and fungi. Despite their longstanding antibacterial history, there is currently a lack of scientific evidence to support their role in the management of infections caused by the nosocomial bacterium, A. baumannii. This study aimed to address this gap in knowledge by examining the antibacterial and lipase inhibitory effects of six commonly consumed Brassica greens, Chinese cabbage (CC), curly and Tuscan kale (CK and TK), red and green Pak choi (RP and GP), and Brussels sprouts (BR), against A. baumannii in relation to their chemical profiles.

METHODS

The secondary metabolites of the six extracts were identified using LC-QTOF-MS/MS analysis, and they were subsequently correlated with the lipase inhibitory activity using multivariate data analysis and molecular docking.

RESULTS

In total, 99 metabolites from various chemical classes were identified in the extracts. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) revealed the chemical similarities and variabilities among the specimens, with glucosinolates and phenolic compounds being the major metabolites. RP and GP showed the highest antibacterial activity against A. baumannii, followed by CK. Additionally, four species showed a significant effect on the bacterial growth curves and demonstrated relevant inhibition of A. baumannii lipolytic activity. CK showed the greatest inhibition (26%), followed by RP (21%), GP (21%), and TK (15%). Orthogonal partial least squares-discriminant analysis (OPLS-DA) pinpointed 9 metabolites positively correlated with the observed bioactivities. Further, the biomarkers displayed good binding affinities towards lipase active sites ranging from -70.61 to -30.91 kcal/mol, compared to orlistat.

CONCLUSION

This study emphasizes the significance of Brassica vegetables as a novel natural source of potential inhibitors of lipase from A. baumannii.

Functional groups matter: metabolomics analysis of Escherichia coli exposed to trans-cinnamic acid and its derivatives unveils common and unique targets

Phenolic acids are derivatives of benzoic and cinnamic acids, which possess important biological activities at certain concentrations. Trans-cinnamic acid (t-CA) and its derivatives, such as p-coumaric acid (p-CA) and ferulic acid (FA) have been shown to have antibacterial activity against various Gram-positive and -negative bacteria. However, there is limited information available concerning the antibacterial mode of action of these phenolic acids. In this study, we aimed to ascertain metabolic alterations associated with exposure to t-CA, p-CA, and FA in Escherichia coli BW25113 using a nuclear magnetic resonance (NMR)-based metabolomics approach. The results showed that t-CA, p-CA, and FA treatments led to significant changes (p < 0.05) in the concentration of 42, 55, and 74% of the identified metabolites in E. coli, respectively. Partial least-squares discriminant analysis (PLS-DA) revealed a clear separation between control and phenolic acid groups with regard to metabolic response. Moreover, it was found that FA and p-CA treatment groups were clustered closely together but separated from the t-CA treatment group. Arginine, putrescine, cadaverine, galactose, and sucrose had the greatest impact on group differentiation. Quantitative pathway analysis demonstrated that arginine and proline, pyrimidine, glutathione, and galactose metabolisms, as well as aminoacyl-tRNA and arginine biosyntheses, were markedly affected by all phenolic acids. Finally, the H2O2 content of E. coli cells was significantly increased in response to t-CA and p-CA whereas all phenolic acids caused a dramatic increase in the number of apurinic/apyrimidinic sites. Overall, this study suggests that the metabolic response of E. coli cells to t-CA is relatively different from that to p-CA and FA. However, all phenolic acids had a certain impact on oxidative/antioxidant status, genomic stability, arginine-related pathways, and nucleic acid metabolism.

Action of crude ethanol extract of Hymenaea martiana leaf, gallic acid, and polypyrrole (PPy) against Aeromonas hydrophila

Pisciculture represents one of the industries with the fastest growth rates worldwide. However, it presents obstacles to its development, such as bacteriosis, which is conventionally treated with antibiotics. The indiscriminate and inappropriate use of antibiotics can lead to bacterial resistance, thus alternatives to the use of antibiotics have been researched. The study aimed to analyze the potential of crude ethanol extract (CEE) from Hymenaea martiana leaf, gallic acid (GA), and polypyrrole (PPy) against Aeromonas hydrophila. Tests were performed to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the compounds individually and in synergy (checkerboard) against A. hydrophila and in silico tests between the compounds evaluated. The CEE of H. martiana leaf and PPy were effective against A. hydrophila with MBC results of 3125 μg/mL for the CEE of H. martiana and 125 μg/mL for PPy. Evaluating the GA, a MIC and MBC of 125 μg/mL was obtained. In the interaction tests (checkerboard, using PPy/CEE and PPy/GA), there was a significant reduction in individual introductions. Thus, for the PPy/CEE tests, we had a reduction of MIC/MBC to 1.95 and 781.25 μg/mL, and for the synergy tests between PPy/GA to 7.8125 and 31.125 μg/mL, respectively. The synergy tests are encouraging, and it is possible to verify a decrease of up to 98% in the introduction of PPy, 75% in CEE for H. martiana and 75.1% for GA, when compared to their individual tests. The tests with GA are encouraging due to GA's effectiveness as an antimicrobial agent and high synergy with polypyrrole, both in vitro results and molecular docking experiments showed the actions at the same activation site in A. hydrophila. In vivo tests evaluating isolated components of CEE from H. martiana in synergy with PPy should be performed, to verify the quality of the interactions and the improvement of the immune responses of the animals. It was evidenced that gallic acid, a substance isolated from the extract, tends to have more promising results. This is relevant since the industry has been developing these compounds for different uses, thus providing easier access to the product. Thus, the present study indicates an efficient alternative in the use of bioactive compounds as substitutes for conventional antimicrobials.

The neuroprotective effect of mesenchymal stem cells in colistin-induced neurotoxicity

Colistin is an effective antibiotic against multidrug-resistant gram-negative bacterial infections; however, neurotoxic effects are fundamental dose-limiting factors for this treatment. Stem cell therapy is a promising method for treating neuronal diseases. Multipotent mesenchymal stromal cells (MSC) represent a promising source for regenerative medicine. Identification of neuroprotective agents that can be co-administered with colistin has the potential to allow the clinical application of this essential drug. This study was conducted to assess the potential protective effects of MSC, against colistin-induced neurotoxicity, and the possible mechanisms underlying any effect. Forty adult female albino rats were randomly classified into four equal groups; the control group, the MSC-treated group (A single dose of 1 × 106/mL MSCs through the tail vein), the colistin-treated group (36 mg/kg/d colistin was given for 7 d) and the colistin and MSC treated group (36 mg/kg/d colistin was administered for 7 d, and 1 × 106/mL MSCs). Colistin administration significantly increased GFAP, NGF, Beclin-1, IL-6, and TNF-α immunreactivity intensity. MSC administration in colistin-treated rats partially restored each of these markers. Histopathological changes in brain tissues were also alleviated by MSC co-treatment. Our study reveals a critical role of inflammation, autophagy, and apoptosis in colistin-induced neurotoxicity and showed that they were markedly ameliorated by MSC co-administration. Therefore, MSC could represent a promising agent for prevention of colistin-induced neurotoxicity.

Redox Impact on Bacterial Macromolecule: A Promising Avenue for Discovery and Development of Novel Antibacterials

Antibiotic resistance in bacteria has remained a serious public health concern, resulting in substantial deaths and morbidity each year. Factors such as mutation and abuse of currently available antibiotics have contributed to the bulk of the menace. Hence, the introduction and implementation of new therapeutic strategies are imperative. Of these strategies, data supporting the role of reactive oxygen species (ROS) in bacterial lethality are intriguing, with several antimicrobials, including antibiotics such as fluoroquinolones, β-lactams, and aminoglycosides, as well as natural plant compounds, being remarkably implicated. Following treatment with ROS-inducing antimicrobials, ROS such as O₂^•-, ^•OH, and H₂O₂ generated in bacteria, which the organism is unable to detoxify, damage cellular macromolecules such as proteins, lipids, and nucleic acids and results in cell death. Despite the unique mechanism of action of ROS-inducing antibacterials and significant studies on ROS-mediated means of bacterial killing, the field remains a topical one, with contradicting viewpoints that require frequent review. Here, we appraised the antibacterial agents (antibiotics, natural and synthetic compounds) implicated in ROS generation and the safety concerns associated with their usage. Further, background information on the sources and types of ROS in bacteria, the mechanism of bacterial lethality via oxidative stress, as well as viewpoints on the ROS hypothesis undermining and solidifying this concept are discussed.

CRISPR-Cas in Acinetobacter baumannii Contributes to Antibiotic Susceptibility by Targeting Endogenous AbaI

Acinetobacter baumannii is a well-known human opportunistic pathogen in nosocomial infections, and the emergence of multidrug-resistant Acinetobacter baumannii has become a complex problem for clinical anti-infective treatments. The ways this organism obtains multidrug resistance phenotype include horizontal gene transfer and other mechanisms, such as altered targets, decreased permeability, increased enzyme production, overexpression of efflux pumps, metabolic changes, and biofilm formation. A CRISPR-Cas system generally consists of a CRISPR array and one or more operons of cas genes, which can restrict horizontal gene transfer in bacteria. Nevertheless, it is unclear how CRISPR-Cas systems regulate antibiotic resistance in Acinetobacter baumannii. Thus, we sought to assess how CRISPR-Cas affects biofilm formation, membrane permeability, efflux pump, reactive oxygen species, and quorum sensing to clarify further the mechanism of CRISPR-Cas regulation of Acinetobacter baumannii antibiotic resistance. In the clinical isolate AB43, which has a complete I-Fb CRISPR-Cas system, we discovered that the Cas3 nuclease of this type I-F CRISPR-Cas system regulates Acinetobacter baumannii quorum sensing and has a unique function in changing drug resistance. As a result of quorum sensing, synthase abaI is reduced, allowing efflux pumps to decrease, biofilm formation to become weaker, reactive oxygen species to generate, and drug resistance to decrease in response to CRISPR-Cas activity. These observations suggest that the CRISPR-Cas system targeting endogenous abaI may boost bacterial antibiotic sensitivity.

IMPORTANCE CRISPR-Cas systems are vital for genome editing, bacterial virulence, and antibiotic resistance. How CRISPR-Cas systems regulate antibiotic resistance in Acinetobacter baumannii is almost wholly unknown. In this study, we reveal that the quorum sensing regulator abaI mRNA was a primary target of the I-Fb CRISPR-Cas system and the cleavage activity of Cas3 was the most critical factor in regulating abaI mRNA degradation. These results advance our understanding of how CRISPR-Cas systems inhibit drug resistance. However, the mechanism of endogenous targeting of abaI by CRISPR-Cas needs to be further explored.

Orientin Enhances Colistin-Mediated Bacterial Lethality through Oxidative Stress Involvement

Bacterial resistance to colistin has prompted the search for alternative strategies to enhance antibacterial potential. Combination therapy remains one of the viable strategies in antibacterial therapy and has been proven to be effective in reducing the risk of resistance. In this study, the potential of orientin for enhancing the antibacterial activity of colistin was assessed against Klebsiella pneumoniae and Pseudomonas aeruginosa in vitro. The involvement of oxidative stress in such enhancement was also assessed. The minimum inhibitory concentrations (MICs) of colistin and orientin were 16 μg/mL and 64 μg/mL against K. pneumoniae and 64 μg/mL and 256 μg/mL against P. aeruginosa respectively. For the combination therapy, orientin potentiates the antibacterial effect of colistin with a friction inhibitory concentration index (FICI) of 0.37 and 0.31 against K. pneumoniae and P. aeruginosa, respectively. This observation suggests a synergistic interaction, with the MIC of colistin being reduced by 3- and 4-fold in the presence of orientin against K. pneumoniae and P. aeruginosa, respectively. Additionally, treatment with the combination of colistin and orientin induced oxidative stress against both organisms through increased cellular levels of superoxide anion radicals with concomitant increase in NAD⁺/NADH and ADP/ATP ratios. These findings suggest that orientin enhanced colistin in the killing of the test bacteria and the cotreatment of colistin and orientin induced oxidative stress, through reactive oxygen species generation, which consequently facilitated bacterial lethality without causing drug-drug interactions. Although, the data presented in this study has supported the capability of orientin for strengthening antibacterial activity of colistin toward the fight against drug-resistant Gram-negative bacteria, studies focusing on the exact target and mechanism of action of orientin are underway.

Cell Membrane Remodeling Mediates Polymyxin B Resistance in Klebsiella pneumoniae: An Integrated Proteomics and Metabolomics Study

Polymyxin B (PB) is introduced into the clinic as the last-line therapy against carbapenem-resistant Klebsiella pneumoniae (CRKP). Unfortunately, increased resistance to PB in Klebsiella pneumoniae (K. pneumoniae) has threatened global health. Resistance of K. pneumoniae to PB was induced by passaging in serial concentrations of PB and determined by microbroth dilution method. Growth characteristics of induced strains including growth curve, reversibility of resistance, and biofilm formation (crystal violet staining method) were measured. This study employed TMT-labeled quantitative proteomics and LC-MS/MS metabolomics analysis to investigate the key biological processes associated with PB resistance in K. pneumoniae. A total of 315 differentially expressed proteins (DEPs) were identified, of which 133 were upregulated and 182 were downregulated in the PB-resistant K. pneumoniae. KEGG enrichment analysis revealed that the DEPs were mainly involved in ATP-binding cassette (ABC) transporters and cationic antimicrobial peptide (CAMP) resistance. Proteins related to central carbon metabolism were inhibited in the PB-resistant K. pneumoniae, but proteins mediating LPS modification were activated. Transcriptional levels of CAMP resistance-related proteins were significantly different between PB-susceptible and -resistant K. pneumoniae. PB treatment led to an increase in reactive oxygen species (ROS) levels of K. pneumoniae. Metabolomics data demonstrated that 23 metabolites were significantly upregulated in PB-resistant K. pneumoniae and 5 were downregulated. The differential metabolites were mainly lipids, including glycerophospholipids, sphingolipids, and fatty acids. Exposure to PB resulted in increased level of phospholipid transport gene mlaF in K. pneumoniae. Our study suggested that membrane remodeling and inhibited central carbon metabolism are conducive to the development of PB resistance in K. pneumoniae.

Astaxanthin-Mediated Bacterial Lethality: Evidence from Oxidative Stress Contribution and Molecular Dynamics Simulation

The involvement of cellular oxidative stress in antibacterial therapy has remained a topical issue over the years. In this study, the contribution of oxidative stress to astaxanthin-mediated bacterial lethality was evaluated in silico and in vitro. For the in vitro analysis, the minimum inhibitory concentration (MIC) of astaxanthin was lower than that of novobiocin against Staphylococcus aureus but generally higher than those of the reference antibiotics against other test organisms. The level of superoxide anion of the tested organisms increased significantly following treatment with astaxanthin when compared with DMSO-treated cells. This increase compared favorably with those observed with the reference antibiotics and was consistent with a decrease in the concentration of glutathione (GSH) and corresponding significant increase in ADP/ATP ratio. These observations are suggestive of probable involvement of oxidative stress in antibacterial capability of astaxanthin and in agreement with the results of the in silico evaluations, where the free energy scores of astaxanthins' complexes with topoisomerase IV ParC and ParE were higher than those of the reference antibiotics. These observations were consistent with the structural stability and compactness of the complexes as astaxanthin was observed to be more stable against topoisomerase IV ParC and ParE than DNA Gyrase A and B. Put together, findings from this study underscored the nature and mechanism of antibacterial action of astaxanthin that could suggest practical approaches in enhancing our current knowledge of antibacterial arsenal and aid in the novel development of alternative natural topo2A inhibitor.

New progress in the pharmacology of protocatechuic acid: A compound ingested in daily foods and herbs frequently and heavily

Protocatechuic acid is a natural phenolic acid, which widely exists in our daily diet and herbs. It is also one of the main metabolites of complex polyphenols, such as anthocyanins and proanthocyanins. In recent years, a large number of studies on the pharmacological activities of protocatechuic acid have emerged. Protocatechuic acid has a wide range of pharmacological activities including antioxidant, anti-inflammatory, neuroprotective, antibacterial, antiviral, anticancer, antiosteoporotic, analgesia, antiaging activties; protection from metabolic syndrome; and preservation of liver, kidneys, and reproductive functions. Pharmacokinetic studies showed that the absorption and elimination rate of protocatechuic acid are faster, with glucuronidation and sulfation being the major metabolic pathways. However, protocatechuic acid displays a dual-directional regulatory effect on some pharmacological activities. When the concentration is very high, it can inhibit cell proliferation and reduce survival rate. This review aims to comprehensively summarize the pharmacology, pharmacokinetics, and toxicity of protocatechuic acid with emphasis on its pharmacological activities discovered in recent 5 years, so as to provide more up-to-date and thorough information for the preclinical and clinical research of protocatechuic acid in the future. Moreover, it is hoped that the clinical application of protocatechuic acid can be broadened, giving full play to its characteristics of rich sources, low toxicity and wide pharmacological activites.

Rapid microevolution of biofilm cells in response to antibiotics

Infections caused by Acinetobacter baumannii are increasingly antibiotic resistant, generating a significant public health problem. Like many bacteria, A. baumannii adopts a biofilm lifestyle that enhances its antibiotic resistance and environmental resilience. Biofilms represent the predominant mode of microbial life, but research into antibiotic resistance has mainly focused on planktonic cells. We investigated the dynamics of A. baumannii biofilms in the presence of antibiotics. A 3-day exposure of A. baumannii biofilms to sub-inhibitory concentrations of antibiotics had a profound effect, increasing biofilm formation and antibiotic resistance in the majority of biofilm dispersal isolates. Cells dispersing from biofilms were genome sequenced to identify mutations accumulating in their genomes, and network analysis linked these mutations to their phenotypes. Transcriptomics of biofilms confirmed the network analysis results, revealing novel gene functions of relevance to both resistance and biofilm formation. This approach is a rapid and objective tool for investigating resistance dynamics of biofilms.

Caffeic acid abrogates 1,3-dichloro-2-propanol-induced hepatotoxicity by upregulating nuclear erythroid-related factor 2 and downregulating nuclear factor-kappa B

1,3-dichloro-2-propanol is a food-borne contaminant reported to cause liver injury. In this study, we evaluated the protective influence of caffeic acid on 1,3-dichloro-2-propanol-induced hepatotoxicity in rats. Rats were randomized into five groups (A-E). Rats received distilled water or caffeic acid (10 or 20 mg/kg body weight) for 7 days. In addition, rats were challenged with 1,3-dichloro-2-propanol on day 7. Caffeic acid prevented 1,3-dichloro-2-propanol-mediated alterations in alkaline phosphatase, alanine and aspartate aminotransferases, albumin and total bilirubin in the serum of rats. Furthermore, caffeic acid lowered superoxide ion, hydrogen peroxide and cytochrome P2E1 while increasing the activities of superoxide dismutase, catalase and glutathione S-transferase in the liver of 1,3-dichloro-2-propanol-treated rats. Caffeic acid raised the levels of nuclear erythroid-related factor 2 (Nrf-2), protein kinase A and phosphoinositide 3-kinase. Caffeic acid pretreatment annulled 1,3-dichloro-2-propanol-mediated alterations in the oxidative stress biomarkers; caspase-3, glutathione, malondialdehyde, protein carbonyl and fragmented DNA, in the liver of rats. Contrastingly, caffeic acid lowered 1,3-dichloro-2-propanol-mediated increase in the levels of nuclear factor-kappa B (NF-κB), tumour necrosis factor-α, interleukin-1β (IL-1β) and IL-6. In addition, caffeic acid preserved the morphological features of 1,3-dichloro-2-propanol-treated rats. Results from this study revealed that caffeic acid protects against 1,3-dichloro-2-propanol-induced hepatotoxicity by enhancing the cytoprotective enzymes through Nrf-2 while lowering inflammation through NF-κB.

Lophirones B and C induce oxidative cellular death pathway in Acinetobacter baumannii by inhibiting DNA gyrase

We evaluated the inactivation of DNA gyrase on the oxidative stress response and sensitivity of A. baumannii to lophirones B and C. The sensitivity of parental and the mutant strains of A. baumannii to lophirones B and C was determined using minimum inhibitory concentration (MIC) and time-kill sensitivity. Inactivation of sodB, katG, recA enhanced the sensitivity of A. baumannii to lophirones B and C. Furthermore, this inactivation increased the accumulation of superoxide anion radical and hydrogen peroxide in lophirones B and C-treated A. baumannii, which was reversed in the presence of thiourea. Inactivation of gyrA stalled lophirones B and C-mediated ROS accumulation in A. baumannii. In addition, lophirones B and C raised the Fe²⁺ contents of A. baumannii. Dipyridyl (Fe chelator) reversed the sensitivity of A. baumannii to lophirones B and C. Lophirones significantly lowered the NAD+/NADH ratio of A. baumannii. The results of this study revealed that the impact of DNA gyrase in lophirones B and C-mediated ROS accumulation, Fe²⁺ release and cell death.

Contributions of reactive oxygen species, oxidative DNA damage and glutathione depletion to the sensitivity of Acinetobacter baumannii to 2-(2-nitrovinyl) furan

2-(2-nitrovinyl) furan is a broad-spectrum antibacterial agent with activity against Gram-positive and Gram-negative bacteria. In this study, the contributions of reactive oxygen species, oxidative DNA damage and glutathione depletion to its activity against Acinetobacter baumannii was investigated. Inactivation of sodB, katG and recA lowered the minimum inhibitory concentration of 2-(2-nitrovinyl) furan. Furthermore, the inactivation increased the superoxide anion radical and hydrogen peroxide contents of 2-(2-nitrovinyl) furan-treated A. baumannii. Antioxidant (thiourea) reversed the elevated levels of superoxide anion radical and hydrogen peroxide. In addition, thiourea lowered the susceptibility of A. baumannii to 2-(2-nitrovinyl) furan. 2-(2-nitrovinyl) furan depleted reduced glutathione (GSH) contents of parental, sodB, katG and recA strains of A. baumannii. NAD+/NADH ratio parental, sodB, katG and recA strains of A. baumannii exposed to 2-(2-nitrovinyl) furan increased significantly. Inactivation of type-I NADH dehydrogenase lowered the reactive oxygen species generation in 2-(2-nitrovinyl) furan-treated A. baumannii. It is evident from this study that 2-(2-nitrovinyl) furan stimulates respiratory chain activity of A. baumannii leading to enhanced ROS generation, which depletes GSH and reacts with Fe²⁺ to produce hydroxyl radical that damage DNA.