A Common Mechanism of Cellular Death Induced by Bactericidal Antibiotics

β-lactam antibiotics induce metabolic perturbations linked to ROS generation leads to bacterial impairment

Understanding the impact of antibiotics on bacterial metabolism is crucial for elucidating their mechanisms of action and developing more effective therapeutic strategies. β-lactam antibiotics, distinguished by their distinctive β-lactam ring structure, are widely used as antimicrobial agents. This study investigates the global metabolic alterations induced by three β-lactam antibiotics-meropenem (a carbapenem), ampicillin (a penicillin), and ceftazidime (a cephalosporin)-in Escherichia coli. Our comprehensive metabolic profiling revealed significant perturbations in bacterial metabolism, particularly in pathways such as glutathione metabolism, pantothenate and CoA biosynthesis, pyrimidine metabolism, and purine metabolism. Antibiotic treatment markedly increased reactive oxygen species levels, with meropenem reaching nearly 200 ± 7%, ampicillin at 174 ± 11%, and ceftazidime at 152 ± 7%. Additionally, β-lactam antibiotics elevated 8-OHdG levels to 4.73 ± 0.56-fold for meropenem, 2.49 ± 0.19-fold for ampicillin, and 3.19 ± 0.34-fold for ceftazidime; 8-OHG levels increased to 5.57 ± 0.72-fold for meropenem, 3.08 ± 0.31-fold for ampicillin, and 4.45 ± 0.66-fold for ceftazidime, indicating that oxidative stress enhances oxidative damage to bacterial DNA and RNA. Notably, we observed a selective upregulation of specific amino acids associated with cellular repair mechanisms, indicating a metabolic adaptation to counteract oxidative damage. These findings illustrate that β-lactam antibiotics induce a complex metabolic perturbations associated with ROS production, potentially compromising critical cellular components. This study enhances our understanding of the intricate relationship between antibiotic action and bacterial metabolism, providing valuable insights for developing effective strategies against antibiotic-resistant pathogens.

Multidrug tolerance conferred by loss-of-function mutations in anti-sigma factor RshA of Mycobacterium abscessus

Low-level drug resistance in noncanonical pathways can constitute steppingstones toward acquisition of high-level on-target resistance mutations in the clinic. To capture these intermediate steps in Mycobacterium abscessus (Mab), we performed classic mutant selection experiments with moxifloxacin at twofold its minimum inhibitory concentration (MIC) on solid medium. We found that low-level resistance emerged reproducibly as loss-of-function mutations in RshA (MAB_3542c), an anti-sigma factor that negatively regulates activity of SigH, which orchestrates a response to oxidative stress in mycobacteria. Since oxidative stress is generated in response to many antibiotics, we went on to show that deletion of rshA confers low to moderate resistance-by measure of MIC-to a dozen agents recommended or evaluated for the treatment of Mab pulmonary infections. Interestingly, this moderate resistance was associated with a wide range of drug tolerance, up to 1,000-fold increased survival of a ΔrshA Mab mutant upon exposure to several β-lactams and DNA gyrase inhibitors. Consistent with the putative involvement of the SigH regulon, we showed that addition of the transcription inhibitor rifabutin (RBT) abrogated the high-tolerance phenotype of ΔrshA to representatives of the β-lactam and DNA gyrase inhibitor classes. In a survey of 10,000 whole Mab genome sequences, we identified several loss-of-function mutations in rshA as well as non-synonymous polymorphisms in two cysteine residues critical for interactions with SigH. Thus, the multidrug multiform resistance phenotype we have uncovered may not only constitute a step toward canonical resistance acquisition during treatment but also contribute directly to treatment failure.

"Nano knife" for efficient piezocatalytic inactivation of amoeba spores and their intracellular bacteria: Synergetic effect between physical damage and chemical oxidation

Microbial interactions between infectious agents severely interfere with the disinfection process, and current disinfection methods are unable to effectively inactivate intracellular pathogens, posing a new threat to drinking water safety. In this study, we first reported the high efficiency of piezocatalysis in inactivating amoebae and their intracellular bacteria. Results showed that the inactivation rates of the MoS2/rGO piezocatalytic system for amoebic spores and their intracellular bacteria were 4.18 and 5.02-log, respectively, within 180 min. Based on scavenger studies and ESR tests, the efficient inactivation of pathogens can be attributed to the generation of reactive oxygen species (ROS), and different pathogens exhibit varying tolerances to distinct ROS. Moreover, TEM analysis revealed that the sharp edge of MoS2/rGO was conducive to the physical cutting of amoeba's cell wall and membrane, promoting the attack of ROS and ensuring a more thorough deactivation. Additionally, the intracellular ROS produced by amoebae is not only conducive to the inactivation of amoebae but also the main reason for the inactivation of bacteria in spores. This study provides a new solution for the inactivation of amoeba spores and their intracellular bacteria and emphasizes the high efficiency of the synergistic effect of physical damage and chemical oxidation.

Metabolic variation and oxidative stress responses of clams (Ruditapes philippinarum) perturbed by ofloxacin exposure

Ofloxacin (OFL), one of the most widely used fluoroquinolone antibiotics, has been frequently detected in marine environments. Nonetheless, researchers are yet to focus on the effects of OFL on the benthos. In the present study, marine clams (Ruditapes philippinarum) were exposed to OFL (0.5, 50, and 500 μg/L) for 14 d, followed by a 7 d depuration period. The accumulation of OFL, antioxidative defense responses, neurotoxicity, burrowing behavior, and metabolomic changes in clams were evaluated. The results indicated that OFL could accumulate in clams, albeit with a low bioaccumulation capacity. The intermediate (50 μg/L) and high (500 μg/L) levels of OFL induced significant antioxidative responses in the gills and digestive glands of clams, mainly manifesting as the inhibition of catalase activities and the induction of superoxide dismutase and glutathione S-transferase activities, which ultimately elevated the content of malondialdehyde, causing oxidative damage. Furthermore, the significant induction of acetylcholinesterase activities was observed, coinciding with a significant increase in burrowing rates of clams. The high level of OFL affected glycerophospholipid, arachidonic acid, steroid hormone biosynthesis, unsaturated fatty acids biosynthesis, and glycolysis/glycogenesis metabolism. In conclusion, this study has contributed to the understanding of the physiological and biochemical effects and molecular toxicity mechanisms of OFL to marine bivalves.

Towards antimicrobial agents: Design and antibacterial activity of a hybrid fluorophore where porphyrin and Rose Bengal moieties are linked through the hydroxyl group of a xanthene dye

The axial complex of Sn(IV)-tetra(4-sulfophenyl)porphyrin (SnP) with Rose Bengal (RB) was obtained where RB axial binding is realized through the hydroxyl groups of the xanthene dye [SnP(RB)2]. The luminescent properties of the SnP(RB)2 (fluorescence and ability to generate singlet oxygen at room temperature) in aqueous media with additives of surfactant cetylpyridinium chloride (CPC) and ε-poly-l-lysine (EPL) were studied. It was found that nature of the medium (surfactant additives of different concentrations) determines the effectiveness of the photoinduced energy transfer from the RB fragment to the SnP fragment of the hybrid fluorophore (HF). It has been established that the ability of the HF to generate singlet oxygen in D2O and D2O-micellar media is higher than that of its constituent fragments. The dark and photodynamic antibacterial activity of the HF against two microorganisms [Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus)] was determined and analyzed. It was shown how the antibacterial activity of the HF depends on the nature of the bacteria, the micellar environment and radiation dose.

A novel cathelicidin TS-CATH derived from Thamnophis sirtalis combats drug-resistant gram-negative bacteria in vitro and in vivo

Antimicrobial peptides are promising therapeutic agents for treating drug-resistant bacterial disease due to their broad-spectrum antimicrobial activity and decreased susceptibility to evolutionary resistance. In this study, three novel cathelicidin antimicrobial peptides were identified from Thamnophis sirtalis, Balaenoptera musculus, and Lipotes vexillifer by protein database mining and sequence alignment and were subsequently named TS-CATH, BM-CATH, and LV-CATH, respectively. All three peptides exhibited satisfactory antibacterial activity and broad antibacterial spectra against clinically isolated E. coli, P. aeruginosa, K. pneumoniae, and A. baumannii in vitro. Among them, TS-CATH displayed the best antimicrobial/bactericidal activity, with a rapid elimination efficiency against the tested drug-resistant gram-negative bacteria within 20 min, and exhibited the lowest cytotoxicity toward mammalian cells. Furthermore, TS-CATH effectively enhanced the survival rate of mice with ceftazidime-resistant E. coli bacteremia and promoted wound healing in meropenem-resistant P. aeruginosa infection. These results were achieved through the eradication of bacterial growth in target organs and wounds, further inhibiting the systemic dissemination of bacteria and the inflammatory response. TS-CATH exhibited direct antimicrobial activity by damaging the inner and outer membranes, resulting in leakage of the bacterial contents at super-MICs. Moreover, TS-CATH disrupted the bacterial respiratory chain, which inhibited ATP synthesis and induced ROS formation, significantly contributing to its antibacterial efficacy at sub-MICs. Overall, TS-CATH has potential for use as an antibacterial agent.

Response of Paenibacillus polymyxa SC2 to the stress of polymyxin B and a key ABC transporter YwjA involved

Polymyxins are cationic peptide antibiotics and regarded as the "final line of defense" against multidrug-resistant bacterial infections. Meanwhile, some polymyxin-resistant strains and the corresponding resistance mechanisms have also been reported. However, the response of the polymyxin-producing strain Paenibacillus polymyxa to polymyxin stress remains unclear. The purpose of this study was to investigate the stress response of gram-positive P. polymyxa SC2 to polymyxin B and to identify functional genes involved in the stress response process. Polymyxin B treatment upregulated the expression of genes related to basal metabolism, transcriptional regulation, transport, and flagella formation and increased intracellular ROS levels, flagellar motility, and biofilm formation in P. polymyxa SC2. Adding magnesium, calcium, and iron alleviated the stress of polymyxin B on P. polymyxa SC2, furthermore, magnesium and calcium could improve the resistance of P. polymyxa SC2 to polymyxin B by promoting biofilm formation. Meanwhile, functional identification of differentially expressed genes indicated that an ABC superfamily transporter YwjA was involved in the stress response to polymyxin B of P. polymyxa SC2. This study provides an important reference for improving the resistance of P. polymyxa to polymyxins and increasing the yield of polymyxins. KEY POINTS: • Phenotypic responses of P. polymyxa to polymyxin B was performed and indicated by RNA-seq • Forming biofilm was a key strategy of P. polymyxa to alleviate polymyxin stress • ABC transporter YwjA was involved in the stress resistance of P. polymyxa to polymyxin B.

Pathogen-encoded Rum DNA polymerase drives rapid bacterial drug resistance

The acquisition of multidrug resistance by pathogenic bacteria is a potentially incipient pandemic. Horizontal transfer of DNA from mobile integrative conjugative elements (ICEs) provides an important way to introduce genes that confer antibiotic (Ab)-resistance in recipient cells. Sizable numbers of SXT/R391 ICEs encode a hypermutagenic Rum DNA polymerase (Rum pol), which has significant homology with Escherichia coli pol V. Here, we show that even under tight transcriptional and post-transcriptional regulation imposed by host bacteria and the R391 ICE itself, Rum pol rapidly accelerates development of multidrug resistance (CIPR, RifR, AmpR) in E. coli in response to SOS-inducing Ab and non-Ab external stressors bleomycin (BLM), ciprofloxacin (CIP) and UV radiation. The impact of Rum pol on the rate of acquisition of drug resistance appears to surpass potential contributions from other cellular processes. We have shown that RecA protein plays a central role in controlling the ability of Rum pol to accelerate antibiotic resistance. A single amino acid substitution in RecA, M197D, acts as a 'Master Regulator' that effectively eliminates the Rum pol-induced Ab resistance. We suggest that Rum pol should be considered as one of the major factors driving development of de novo Ab resistance in pathogens carrying SXT/R391 ICEs.

Resensitization of Multi Drug-Resistant Aeromonas caviae with Exogenous Hydrogen Sulfide Potentiated Antibiotics

Antimicrobial resistance (AMR) is a growing public health threat caused by the widespread overuse of antibiotics. Bacteria with antibiotic resistance may acquire resistance genes from soil or water. Endogenous hydrogen sulfide (H2S) production in bacteria confers antibiotic tolerance in many, suggesting a universal defense mechanism against antibiotics. In this study, we isolated and identified soil-based antibiotic-resistant bacteria collected from contaminated areas. An antibiotic-resistant bacterium was identified as non-endogenous-H2S-producing, allowing us to examine the effect of exogenous H2S on its resistance mechanism. Therefore, we demonstrated that different classes of antibiotic resistance can be reverted by employing H2S with antibiotics like ampicillin and gentamicin. Methods like Kirby-Bauer Disk-Diffusion, Scanning Electron Microscopy, and Flow Cytometer analysis were performed to assess the antibacterial activity of H2S with ampicillin and gentamicin. The antioxidative efficiency of H2S was evaluated using the DCFH-DA (ROS) test, as well as lipid peroxidation, and LDH activity. These were further confirmed with enzymatic and non-enzymatic (SOD, CAT, GST, and GSH) antioxidant studies. These findings support H2S as an antibiotic-potentiator, causing bacterial membrane damage, oxidative stress, and disrupting DNA and proteins. Thus, supplying exogenous H2S can be a good agent for the reversal of Antibiotic resistance.

Microbial biofilms: a comprehensive review of their properties, beneficial roles and applications

Biofilms are microbial communities nested in self-secreted extracellular polymeric substances that can provide microorganisms with strong tolerance and a favorable living environment. Deepening the understanding and research on positive effects of microbial biofilms is consequently necessary, since most researches focuses on how to control biofilms formation to reduce food safety issues. This paper highlights beneficial roles of biofilms including the formation mechanism, influencing factors, health benefits, strategies to improve its film-forming efficiency, as well as applications especially in fields of food industry, agriculture and husbandry, and environmental management. Beneficial biofilms can be affected by multiple factors such as strain characteristics, media composition, signal molecules, and carrier materials. The biofilm barrier composed of beneficial bacteria provides a more favorable microecological environment, keeping bacteria survival longer, and its derived metabolites are better conducive to health. However, in the practical application of biofilms, there are still significant challenges, especially in terms of film-forming efficiency, stability, and safety assessment. Continuous research is needed to discover innovative methods of utilizing biofilms for sustainable food development in the future, in order to fully unleash its potential and promote its application in the food industry.

Phage cocktail amikacin combination as a potential therapy for bacteremia associated with carbapenemase producing colistin resistant Klebsiella pneumoniae

The increasing occurrence of hospital-associated infections, particularly bacteremia, caused by extensively drug-resistant (XDR) carbapenemase-producing colistin-resistant Klebsiella pneumoniae highlights a critical requirement to discover new therapeutic alternatives. Bacteriophages having host-specific bacteriolytic effects are promising alternatives for combating these pathogens. Among 12 phages isolated from public wastewater in Thailand, two phages-vB_kpnM_05 (myovirus) and vB_kpnP_08 (podovirus) showed broad-host range, producing bacteriolytic activities against 81.3% (n = 26) and 78.1% (n = 25) of 32 XDR carbapenemase-producing colistin-resistant K. pneumoniae, with capsular types-K15, K17, K50, K51, K52/wzi-50 and K2/wzi-2. Both phages showed short replication times, large burst sizes with rapid adsorptions. They exhibited significant stability under various environmental conditions. Genomic analysis revealed that both phages are genetically distinct phages from Myoviridae and Podoviridae family, with the lack of toxin, virulence, lysogeny and antibiotic resistance genes. These characteristics highlighted their promising potential for utilizing in phage therapy for combating XDR K. pneumoniae. Although phage cocktail combining vB_kpnM_05 and vB_kpnP_08 provided significant bacteriolysis for longer duration (8 h) than its monophage (6 h), bacterial regrowth was observed which suggested an evitable development of phage resistance under phages' selection pressures. Future study will be undertaken to elucidate the precise mechanisms by which these XDR K. pneumoniae developed phage resistance and their associated fitness cost. Remarkably, combining phage cocktail with amikacin at their sub-inhibitory concentrations produced potent synergy by completely suppressing bacterial regrowth in vitro. Our study demonstrated the significant therapeutic and prophylactic effectiveness of a phage cocktail-amikacin combination as a promising alternative strategy for overcoming bacteremia associated with XDR K. pneumoniae having carbapenemase and colistin resistance in vivo.

Discovery of antibacterial diketones against gram-positive bacteria

The rapid rise of antibiotic resistance calls for the discovery of new antibiotics with distinct antibacterial mechanisms. New target mining is indispensable for developing antibiotics. Plant-microbial antibiotics are appealing to underexplored sources due to a dearth of comprehensive understanding of antibacterial activity and the excavation of new targets. Here, a series of phloroglucinol derivatives of plant-root-associated Pseudomonas fluorescens were synthesized for structure-activity relationship analysis. Notably, 2,4-diproylphloroglucinol (DPPG) displayed efficient bactericidal activity against a wide range of gram-positive bacteria. Importantly, mechanistic study exhibits that DPPG binds to type II NADH dehydrogenase (NDH-2), an essential enzyme catalyzing the transfer of electrons from NADH to quinones in the electron transport chain (ETC), blocking electron transfer in S. aureus. Last, we validated the efficacy of DPPG in vivo through animal infection models. Our findings not only provide a distinct antibiotic lead to treat multidrug resistant pathogens but also identify a promising antibacterial target.

Whole genome CRISPRi screening identifies druggable vulnerabilities in an isoniazid resistant strain of Mycobacterium tuberculosis

Drug-resistant strains of Mycobacterium tuberculosis are a major global health problem. Resistance to the front-line antibiotic isoniazid is often associated with mutations in the katG-encoded bifunctional catalase-peroxidase. We hypothesise that perturbed KatG activity would generate collateral vulnerabilities in isoniazid-resistant katG mutants, providing potential pathway targets to combat isoniazid resistance. Whole genome CRISPRi screens, transcriptomics, and metabolomics were used to generate a genome-wide map of cellular vulnerabilities in an isoniazid-resistant katG mutant strain of M. tuberculosis. Here, we show that metabolic and transcriptional remodelling compensates for the loss of KatG but in doing so generates vulnerabilities in respiration, ribosome biogenesis, and nucleotide and amino acid metabolism. Importantly, these vulnerabilities are more sensitive to inhibition in an isoniazid-resistant katG mutant and translated to clinical isolates. This work highlights how changes in the physiology of drug-resistant strains generates druggable vulnerabilities that can be exploited to improve clinical outcomes.

Small RNA OxyS induces resistance to aminoglycosides during oxidative stress by controlling Fe-S cluster biogenesis in Escherichia coli

Fe-S clusters are essential cofactors involved in many reactions across all domains of life. Their biogenesis in Escherichia coli and other enterobacteria involves two machineries: Isc and Suf. Under conditions where cells operate with the Suf system, such as during oxidative stress or iron limitation, the entry of aminoglycosides is reduced, leading to resistance to these antibiotics. The transition between Isc and Suf machineries is controlled by the transcriptional regulator IscR. Here, we found that two small regulatory RNAs (sRNAs), FnrS and OxyS, control iscR expression by base pairing to the 5'-UTR of the iscR mRNA. These sRNAs act in opposite ways and in opposite conditions: FnrS, expressed in anaerobiosis, represses the expression of iscR while OxyS, expressed during oxidative stress, activates it. Using an E. coli strain experiencing protracted oxidative stress, we further demonstrate that iscR expression is rapidly and significantly enhanced in the presence of OxyS. Consequently, we further show that OxyS induces resistance to aminoglycosides during oxidative stress through regulation of Fe-S cluster biogenesis, revealing a major role for this sRNA.

Overexpression of l,d-Transpeptidase A Induces Dispensability of Rod Complex in Escherichia coli

Antimicrobial resistance (AMR) is a significant global threat, and the presence of resistance-determinant genes is one of the major driving forces behind it. The bacterial rod complex is an essential set of proteins that is crucial for cell survival due to its role in cell wall biogenesis and shape maintenance. Therefore, these proteins offer excellent potential as drug targets; however, compensatory mutations in nontarget genes render this complex nonessential. The MreB protein of this complex is an actin homologue that rotates along the longitudinal axis of the cell to provide rod shape to the bacteria. In this study, using chemical-chemical interaction profiling and FtsZ suppression assay, we identified the MreB targeting activity of IITR07865, a previously discovered small molecule in our lab. Escherichia coli suppressors against IITR07865 revealed mutations in two cell division-associated genes, min C and pal, that have not been previously implicated in rod complex essentiality. IITR07865 resistant mutants were found to inactivate and render the rod complex nonessential, making the rod complex inhibitors ineffective. Further, through transcriptome analysis, we reveal the primary cause of resistance in suppressor strains to be the overexpression of an l, d-transpeptidase A enzyme, which is involved in peptidoglycan and Braun's lipoprotein cross-linking. Our results demonstrate a novel mechanism of resistance development in rod-shaped Gram-negative bacterial pathogen E. coli involved in UTIs where mecillinam, a clinically used antibiotic that targets rod complex, is a drug of choice.

Effect of H2S and cysteine homeostasis disturbance on ciprofloxacin sensitivity of Escherichia coli in cystine-free and cystine-fed minimal medium

Endogenous H2S has been proposed to be a universal defense mechanism against different antibiotics. Here, we studied the role of H2S transiently generated during ciprofloxacin (CF) treatment in M9 minimal medium with sulfate or produced by E. coli when fed with cystine. The cysM and mstA mutants did not produce H2S, while gshA generated more H2S in response to ciprofloxacin in cystine-free media. All mutants showed a reduced ability to maintain cysteine homeostasis under these conditions. We found no relationship between H2S generation, cysteine concentration and sensitivity to ciprofloxacin. Excess cysteine, which occurred during E. coli growth in cystine-fed media, triggered continuous H2S production, accelerated glutathione synthesis and cysteine export. This was accompanied by a twofold increase in ciprofloxacin tolerance in all strains except gshA, whose sensitivity increased 5-8-fold at high CF doses, indicating the importance of GSH in restoring the intracellular redox situation during growth in cystine-fed media.

Targeting bacterial phospholipids and their synthesis pathways for antibiotic discovery

Bacterial infections in humans and animals caused by multidrug-resistant (MDR) pathogens pose a serious threat to public health. New antibacterial targets are extremely urgent to solve the dilemma of cross-resistance. Phospholipids are critical components in bacterial envelopes and involve diverse crucial processes to maintain homeostasis and modulate metabolism. Targeting phospholipids and their synthesis pathways has been largely overlooked because conventional membrane-targeted substances are non-specific with cytotoxicity. In this review, we first introduce the structure and physiological function of phospholipids in bacteria. Subsequently, we describe the chemical diversity of novel ligands targeting phospholipids, structure-activity relationships (SAR), modes of action (MOA), and pharmacological effects. Finally, we prospect the advantage of bacterial phospholipids as promising antibacterial targets. In conclusion, these findings will shed light on discovering and developing new antibacterial drugs to combat MDR bacteria-associated infections.

Cell Growth and Division of Staphylococcus aureus

Bacterial cell growth and division require temporal and spatial coordination of multiple processes to ensure viability and morphogenesis. These mechanisms both determine and are determined by dynamic cellular structures and components, from within the cytoplasm to the cell envelope. The characteristic morphological changes during the cell cycle are largely driven by the architecture and mechanics of the cell wall. A constellation of proteins governs growth and division in Staphylococcus aureus, with counterparts also found in other organisms, alluding to underlying conserved mechanisms. Here, we review the status of knowledge regarding the cell cycle of this important pathogen and describe how this informs our understanding of the action of antibiotics and the specter of antimicrobial resistance.

The generation and transformation mechanisms of reactive oxygen species in the environment and their implications for pollution control processes: A review

Reactive oxygen species (ROS), substances with strong activity generated by oxygen during electron transfer, play a significant role in the decomposition of organic matter in various environmental settings, including soil, water and atmosphere. Although ROS has a short lifespan (ranging from a few nanoseconds to a few days), it continuously generated during the interaction between microorganisms and their environment, especially in environments characterized by strong ultraviolet radiation, fluctuating oxygen concentration or redox conditions, and the abundance of metal minerals. A comprehensive understanding of the fate of ROS in nature can provide new ideas for pollutant degradation and is of great significance for the development of green degradation technologies for organic pollutants. At present, the review of ROS generally revolves around various advanced oxidation processes, but lacks a description and summary of the fate of ROS in nature, this article starts with the definition of reactive oxidants species and reviews the production, migration, and transformation mechanisms of ROS in soil, water and atmospheric environments, focusing on recent developments. In addition, the stimulating effects of ROS on organisms were reviewed. Conclusively, the article summarizes the classic processes, possible improvements, and future directions for ROS-mediated degradation of pollutants. This review offers suggestions for future research directions in this field and provides the possible ROS technology application in pollutants treatment.

Isobavachalcone enhances sensitivity of colistin-resistant Klebsiella pneumoniae: In vitro and in vivo proof-of-concept studies

OBJECTIVE

Antibiotic resistance poses a considerable worldwide concern, particularly in clinical environments where drug-resistant Gram-negative bacteria like Klebsiella pneumoniae (K. pneumoniae) present a major challenge. The objective of this research was to investigate the mechanisms by which isobavachalcone (IBC) restores the sensitivity of K. pneumoniae to colistin in vitro and to validate the synergistic therapeutic effect in vivo.

RESULTS

The results indicate that the combined administration of colistin and IBC exhibits a potent antibacterial effect both in vitro and in vivo. The in vitro concurrent administration of colistin and IBC resulted in increased membrane permeability, compromised cell integrity, diminished membrane fluidity, and disrupted membrane homeostasis. Additionally, this combination reduced biofilm production, inhibited the synthesis of the autoinducer factor, altered membrane potential, and affected levels of reactive oxygen species and adenosine triphosphate synthesis, ultimately leading to bacterial death. In vivo experiments on Galleria mellonella and mice demonstrated that the co-administration of colistin and IBC increased the survival rate and significantly reduced pathological damage compared to colistin alone.

CONCLUSION

These results suggested that IBC effectively restores the sensitivity of colistin by inducing physical disruption of bacterial membranes and oxidative stress. The combination therapy of colistin and IBC presents a viable and safe strategy to combat drug-resistant K. pneumoniae-associated infections.

Anticancer agent 5-fluorouracil reverses meropenem resistance in carbapenem-resistant Gram-negative pathogens

The global increasing incidence of clinical infections caused by carbapenem-resistant Gram-negative pathogens requires urgent and effective treatment strategies. Antibiotic adjuvants represent a promising approach to enhance the efficacy of meropenem against carbapenem-resistant bacteria. This study shows that the anticancer agent 5-fluorouracil (5-FU, 50 µM) significantly reduced the minimum inhibitory concentration of meropenem against blaNDM-5 positive Escherichia coli by 32-fold through cell-based high-throughput screening. Further pharmacological studies indicated that 5-FU exhibited potentiation effects on carbapenem antibiotics against 42 Gram-negative bacteria producing either metallo-β-lactamases (MBLs), such as NDM and IMP, or serine β-lactamases (Ser-BLs), like KPC and OXA. These bacteria included E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter spp., 32 of which were obtained from human clinical samples. Mechanistic investigations revealed that 5-FU inhibited the transcription and expression of the blaNDM-5 gene. In addition, 5-FU combined with meropenem enhanced bacterial metabolism, and stimulated the production of reactive oxygen species (ROS), thereby rendering bacteria more susceptible to meropenem. In a mouse systemic infection model, 5-FU combined with meropenem reduced bacterial loads and effectively elevated the survival rate of 83.3%, compared with 16.7% with meropenem monotherapy. Collectively, these findings indicate the potential of 5-FU as a novel meropenem adjuvant to improve treatment outcomes against infections caused by carbapenem-resistant bacteria.

Reactive Oxygen Detoxification Contributes to Mycobacterium abscessus Antibiotic Survival

When a population of bacteria encounter a bactericidal antibiotic most cells die rapidly. However, a sub-population, known as "persister cells", can survive for prolonged periods in a non-growing, but viable, state. Persister cell frequency is dramatically increased by stresses such as nutrient deprivation, but it is unclear what pathways are required to maintain viability, and how this process is regulated. To identify the genetic determinants of antibiotic persistence in mycobacteria, we carried out transposon mutagenesis high-throughput sequencing (Tn-Seq) screens in Mycobacterium abscessus (Mabs). This analysis identified genes essential in both spontaneous and stress-induced persister cells, allowing the first genetic comparison of these states in mycobacteria, and unexpectedly identified multiple genes involved in the detoxification of reactive oxygen species (ROS). We found that endogenous ROS were generated following antibiotic exposure, and that the KatG catalase-peroxidase contributed to survival in both spontaneous and starvation-induced persisters. We also found that that hypoxia significantly impaired bacterial killing, and notably, in the absence of oxygen, KatG became dispensable. Thus, the lethality of some antibiotics is amplified by toxic ROS accumulation, and persister cells depend on detoxification systems to remain viable.

Restoring Colistin Sensitivity in Multidrug-Resistant Pathogenic E. coli Using Cinacalcet Hydrochloride

Restoring colistin's efficacy is crucial in addressing the resistance crisis of colistin. This study utilized a high-throughput screening method to identify 43 compounds from 800 FDA-approved drugs that exhibited significant antibacterial effects when combined with colistin. Among these, cinacalcet hydrochloride (CH) was selected for its potential synergistic effect with colistin against multidrug-resistant (MDR) E. coli strains, including mcr-1-positive strains. A series of experiments revealed that the combination of CH and colistin showed strong synergy, especially in mcr-1-positive strains, restoring colistin sensitivity. The combination significantly inhibited bacterial growth and reduced CFU counts more effectively than either drug alone. Additionally, CH and colistin together significantly inhibited biofilm formation and eradicated existing biofilms, as visualized through confocal microscopy. Mechanistic studies showed that the combination increased bacterial membrane permeability and disrupted membrane integrity. The treatment also elevated extracellular ATP release and ROS production, indicating oxidative stress-induced bacterial death. Safety evaluations showed that the combination did not increase toxicity in host cells. Finally, animal models further validated the combination's efficacy. Overall, this study showed that the combination of colistin and CH significantly restored colistin sensitivity in mcr-1-positive E. coli, revealing their synergistic antibacterial mechanism involving membrane damage and oxidative stress, with promising clinical applications.

Synergistic effect of fosfomycin and colistin against KPC-producing Klebsiella pneumoniae: pharmacokinetics-pharmacodynamics combined with transcriptomic approach

OBJECTIVES

The aim of this study was to identify the synergistic effect and mechanisms of fosfomycin (FM) combined with colistin (COL) against KPC-producing Klebsiella pneumoniae (KPC-Kp).

METHODS

The bactericidal effects, induced drug resistance and cytotoxicity of FM combined with COL were evaluated by time-kill assays and mutation rate test. Time-kill assays and transcriptomics analysis were used to further clarify the mechanism of FM combined with COL. The bacteria were taken from different points in time-kill assays, reactive oxygen species (ROS), nitric oxide and redox related enzymes were detected. The mechanism of synergistic bactericidal action was analyzed by transcriptome.

RESULTS

The bactericidal effect of FM combined with COL was better than that of monotherapy. The mutation frequency of FM alone at low dose (8 mg/L) was higher than that at high dose (64 mg/L). COL induced resistant isolates resulted in FM and COL resistance, while FM alone or combined with COL only resulted in FM resistance. The survival rate of Thp-1 cells in FM combined with COL against K. pneumoniae was higher than that of monotherapy. The intracellular nitric oxide, activities of total superoxide dismutase and catalase were increased along with the increase of FM concentration against KPC-Kp. FM combined with COL induced ROS accumulation and antioxidant capacity increase. Transcriptome analysis showed FM combined with COL could regulate the levels of soxRS and oxidative phosphorylation, in order to clear ROS and repair damage. In addition, FM combined with COL could result in synergetic bactericidal efficacy by inhibiting ribosomal transcription.

CONCLUSIONS

FM combined with COL mediated synergistic bactericidal effect by regulating ROS accumulation and inhibiting ribosomal protein transcription, resulting in lower resistance and cytotoxicity.

Differential effects of inosine monophosphate dehydrogenase (IMPDH/GuaB) inhibition in Acinetobacter baumannii and Escherichia coli

Inosine 5'-monophosphate dehydrogenase (IMPDH), known as GuaB in bacteria, catalyzes the rate-limiting step in de novo guanine biosynthesis and is conserved from humans to bacteria. We developed a series of potent inhibitors that selectively target GuaB over its human homolog. Here, we show that these GuaB inhibitors are bactericidal, generate phenotypic signatures that are distinct from other antibiotics, and elicit different time-kill kinetics and regulatory responses in two important Gram-negative pathogens: Acinetobacter baumannii and Escherichia coli. Specifically, the GuaB inhibitor G6 rapidly kills A. baumannii but only kills E. coli after 24 h. After exposure to G6, the expression of genes involved in purine biosynthesis and stress responses change in opposite directions while siderophore biosynthesis is downregulated in both species. Our results suggest that different species respond to GuaB inhibition using distinct regulatory programs and possibly explain the different bactericidal kinetics upon GuaB inhibition. The comparison highlights opportunities for developing GuaB inhibitors as novel antibiotics.IMPORTANCEA. baumannii is a priority bacterial pathogen for which development of new antibiotics is urgently needed due to the emergence of multidrug resistance. We recently developed a series of specific inhibitors against GuaB, a bacterial inosine 5'-monophosphate dehydrogenase, and achieved sub-micromolar minimum inhibitory concentrations against A. baumannii. GuaB catalyzes the rate-limiting step of de novo guanine biosynthesis and is highly conserved across bacterial pathogens. This study shows that inhibition of GuaB induced a bacterial morphological profile distinct from that of other classes of antibiotics, highlighting a novel mechanism of action. Moreover, our transcriptomic analysis showed that regulation of de novo purine biosynthesis and stress responses of A. baumannii upon GuaB inhibition differed significantly from that of E. coli.

Colistin-niclosamide-loaded nanoemulsions and nanoemulsion gels for effective therapy of colistin-resistant Salmonella infections

Colistin (COL) is regarded as a last-resort treatment for infections by multidrug-resistant (MDR) Gram-negative bacteria. The emergence of colistin-resistant Enterobacterales poses a significant global public health concern. Our study discovered that niclosamide (NIC) reverses COL resistance in Salmonella via a checkerboard assay. However, poor solubility and bioavailability of NIC pose challenges. In this study, we prepared a self-nanoemulsifying drug delivery system (SNEDDS) co-encapsulating NIC and COL. We characterized the physicochemical properties of the resulting colistin-niclosamide-loaded nanoemulsions (COL/NIC-NEs) and colistin-niclosamide-loaded nanoemulsion gels (COL/NIC-NEGs), assessing their antibacterial efficacy in vitro and in vivo. The COL/NIC-NEs exhibited a droplet size of 19.86 nm with a zeta potential of -1.25 mV. COL/NIC-NEs have excellent stability, significantly enhancing the solubility of NIC while also demonstrating a pronounced sustained-release effect. Antimicrobial assays revealed that the MIC of COL in COL/NIC-NEs was reduced by 16-128 times compared to free COL. Killing kinetics and scanning electron microscopy confirmed enhanced antibacterial activity. Antibacterial mechanism studies reveal that the COL/NIC-NEs and COL/NIC-NEGs could enhance the bactericidal activity by damaging cell membranes, disrupting proton motive force (PMF), inhibiting multidrug efflux pump, and promoting oxidative damage. The therapeutic efficacy of the COL/NIC-NEs and COL/NIC-NEGs is further demonstrated in mouse intraperitoneal infection models with COL-resistant Salmonella. To sum up, COL/NIC-NEs and COL/NIC-NEGs are a potentially effective strategies promising against COL-resistant Salmonella infections.

Purine and pyrimidine synthesis differently affect the strength of the inoculum effect for aminoglycoside and β-lactam antibiotics

The inoculum effect has been observed for nearly all antibiotics and bacterial species. However, explanations accounting for its occurrence and strength are lacking. Previous work found that the relationship between [ATP] and growth rate can account for the strength and occurrence of the inoculum effect for bactericidal antibiotics. However, the molecular pathway(s) underlying this relationship, and therefore determining the inoculum effect, remain undiscovered. Using a combination of flux balance analysis and experimentation, we show that nucleotide synthesis can determine the relationship between [ATP] and growth and thus the strength of inoculum effect in an antibiotic class-dependent manner. If the [ATP]/growth rate is sufficiently high as determined by exogenously supplied nitrogenous bases, the inoculum effect does not occur. This is consistent for both Escherichia coli and Pseudomonas aeruginosa. Interestingly, and separate from activity through the tricarboxylic acid cycle, we find that transcriptional activity of genes involved in purine and pyrimidine synthesis can predict the strength of the inoculum effect for β-lactam and aminoglycosides antibiotics, respectively. Our work highlights the antibiotic class-specific effect of purine and pyrimidine synthesis on the severity of the inoculum effect, which may pave the way for intervention strategies to reduce the inoculum effect in the clinic.

IMPORTANCE

If a bacterial population can grow and reach a sufficiently high density, routine doses of antibiotics can be ineffective. This phenomenon, called the inoculum effect, has been observed for nearly all antibiotics and bacterial species. It has also been reported to result in antibiotic failure in the clinic. Understanding how to reduce the inoculum effect can make high-density infections easier to treat. Here, we show that purine and pyrimidine synthesis affect the strength of the inoculum effect; as the transcriptional activity of pyrimidine synthesis increases, the strength of the inoculum effect for aminoglycosides decreases. Conversely, as the transcriptional activity of purine synthesis increases, the strength of the inoculum effect for β-lactam antibiotics decreases. Our work highlights the importance of nucleotide synthesis in determining the strength of the inoculum effect, which may lead to the identification of new ways to treat high-density infections in the clinic.

Efflux pumps mediate changes to fundamental bacterial physiology via membrane potential

Efflux pumps are well known to be an important mechanism for removing noxious substances such as antibiotics from bacteria. Given that many antibiotics function by accumulating inside bacteria, efflux pumps contribute to resistance. Efflux pump inactivation is a potential strategy to combat antimicrobial resistance, as bacteria would not be able to pump out antibiotics. We recently discovered that the impact of loss of efflux function is only apparent in actively growing cells. We demonstrated that the global transcriptome of Salmonella Typhimurium is drastically altered during slower growth leading to stationary-phase cells having a remodeled, less permeable envelope that prevents antibiotics entering the cell. Here, we investigated the effects of deleting the major efflux pump of Salmonella Typhimurium, AcrB, on global gene transcription across growth. We revealed that an acrB knockout entered stationary phase later than the wild-type strain SL1344 and displayed increased and prolonged expression of genes responsible for anaerobic energy metabolism. We devised a model linking efflux and membrane potential, whereby deactivation of AcrB prevents influx of protons across the inner membrane and thereby hyperpolarization. Knockout or deactivation of AcrB was demonstrated to increase membrane potential. We propose that the global transcription regulator ArcBA senses changes to the redox state of the quinol pool (linked to the membrane potential of the bacterium) and coordinates the shift from exponential to stationary phase via the key master regulators RpoS, Rsd, and Rmf. Inactivation of efflux pumps therefore influences the fundamental physiology of Salmonella, with likely impacts on multiple phenotypes.IMPORTANCEWe demonstrate for the first time that deactivation of efflux pumps brings about changes to gross bacterial physiology and metabolism. Rather than simply being a response to noxious substances, efflux pumps appear to play a key role in maintenance of membrane potential and thereby energy metabolism. This discovery suggests that efflux pump inhibition or inactivation might have unforeseen positive consequences on antibiotic activity. Given that stationary-phase bacteria are more resistant to antibiotic uptake, late entry into stationary phase would prolong antibiotic accumulation by bacteria. Furthermore, membrane hyperpolarization could result in increased generation of reactive species proposed to be important for the activity of some antibiotics. Finally, changes in gross physiology could also explain the decreased virulence of efflux mutants.

Combined ozonation-biological activated carbon process for antibiotic resistance control in treated effluent from wastewater treatment plant

Biological activated carbon (BAC) treatment plays a crucial role in wastewater treatment plants due to its economic and effective promotion of organic matter degradation or mineralization. However, whether the changes in antibiotic resistance (AR) resulting from BAC or O3-BAC treatment are related to environmental factors remains unclear, as previous studies have primarily focused on isolated aspects, or have combined these aspects without systematically comparing the BAC and O3-BAC treatment processes or analyzing their interrelationships. In this study, to gain a clearer understanding of the factors related to AR during the BAC treatment, the treatment process of BAC and O3-BAC were comprehensively compared, including antibiotics removal, wastewater matrix changes, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and bacterial community characteristics. The roles of O3 pretreatment and the bed depth of BAC were also clarified. ARGs were found to be not as sensitive to ozone as ARB. In addition, further strengthening of control measures should be needed for trimethoprim and tetracycline, due to their low removal efficiencies by ozone pretreatment, and their close relationship with the increased AR. Besides, 2 mg/L ozonation pretreatment could significantly influence the microbial community composition of wastewater and biofilm samples, while 1 mg/L ozonation could not. Finally, the correlation of environmental factors, bacterial communities, and ARGs revealed that to reduce the AR risks of O3-BAC treatment, antibiotics in wastewater should be strictly controlled, since they were positively correlated with the accumulation of ARGs and Pseudomonadota, Actinomycetota, and Bacteroidota, which were responsible for carrying and disseminating ARGs. The results showed that higher dose ozonation pre-treatment and longer bed depth of BAC process could help control the AR of BAC.

Natural Organic Matter Enhances Natural Transformation of Extracellular Antibiotic Resistance Genes in Sunlit Water

Antibiotic resistance genes (ARGs) as emerging environmental contaminants exacerbate the risk of spreading antibiotic resistance. Natural organic matter (NOM) is ubiquitous in aquatic environments and plays a crucial role in biogeochemical cycles. However, its impact on the dissemination of extracellular antibiotic resistance genes (eARGs) under sunlight exposure remains elusive. This study reveals that environmentally relevant levels of NOM (0.1-20 mg/L) can significantly enhance the natural transformation frequency of the model bacterium Acinetobacter baylyi ADP1 by up to 7.6-fold under simulated sunlight. Similarly, this enhancement was consistently observed in natural water and wastewater systems. Further mechanism analysis revealed that reactive oxygen species (ROS) generated by NOM under sunlight irradiation, primarily singlet oxygen and hydroxyl radicals, play a crucial role in this process. These ROS induce intracellular oxidative stress and elevated cellular membrane permeability, thereby indirectly boosting ATP production and enhancing cell competence of extracellular DNA uptake and integration. Our findings highlight a previously underestimated role of natural factors in the dissemination of eARGs within aquatic ecosystems and deepen our understanding of the complex interplay between NOM, sunlight, and microbes in environmental water bodies. This underscores the importance of developing comprehensive strategies to mitigate the spread of antibiotic resistance in aquatic environments.

Genomic and functional divergence of Staphylococcus aureus strains from atopic dermatitis patients and healthy individuals: insights from global and local scales

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease worldwide and is characterized by a complex interplay with skin microbiota, with Staphylococcus aureus often abnormally more abundant in AD patients than in healthy individuals (HE). S. aureus harbors diverse strains with varied genetic compositions and functionalities, which exhibit differential connections with the severity of AD. However, the differences in S. aureus strains between AD and HE remain unclear, with most variations seen at a specific geographic level, implying spontaneous adaptations rather than systematic distinctions. This study presents genomic and functional differences between these S. aureus strains from AD and HE on both global and local levels. We observed reduced gene content diversity but increased functional variation in the global AD-associated strains. Two additional AD-dominant clusters emerged, with Cluster 1 enriched in transposases and Cluster 2 showcasing genes linked to adaptability and antibiotic resistance. Particularly, robust evidence illustrates that the lantibiotic operon of S. aureus, involved in the biosynthesis of lantibiotics, was acquired via horizontal gene transfer from environmental bacteria. Comparisons of the gene abundance profiles in functional categories also indicate limited zoonotic potential between human and animal isolates. Local analysis mirrored global gene diversity but showed distinct functional variations between AD and HE strains. Overall, this research provides foundational insights into the genomic evolution, adaptability, and antibiotic resistance of S. aureus, with significant implications for clinical microbiology.IMPORTANCEOur study uncovers significant genomic variations in Staphylococcus aureus strains associated with atopic dermatitis. We observed adaptive evolution tailored to the disease microenvironment, characterized by a smaller pan-genome than strains from healthy skin both on the global and local levels. Key functional categories driving strain diversification include "replication and repair" and "transporters," with transposases being pivotal. Interestingly, the local strains predominantly featured metal-related genes, whereas global ones emphasized antimicrobial resistances, signifying scale-dependent diversification nuances. We also pinpointed horizontal gene transfer events, indicating interactions between human-associated and environmental bacteria. These insights expand our comprehension of S. aureus's genetic adaptation in atopic dermatitis, yielding valuable implications for clinical approaches.

Genetic determinants of increased sodium hypochlorite and ciprofloxacin susceptibility in Pseudomonas aeruginosa PA14 biofilms

Reactive chlorine species (RCS) like sodium hypochlorite (NaOCl) are potent oxidizing agents and widely used biocides in surface disinfection, water treatment, and biofilm elimination. Moreover, RCS are also produced by the human immune system to kill invading pathogens. However, bacteria have developed mechanisms to survive the damage caused by RCS. Using the comprehensive Pseudomonas aeruginosa PA14 transposon mutant library in a genetic screen, we identified a total of 28 P. aeruginosa PA14 mutants whose biofilms showed increased susceptibility to NaOCl in comparison to PA14 WT biofilms. Of these, ten PA14 mutants with a disrupted apaH, PA0793, acsA, PA1506, PA1547, PA3728, yajC, queA, PA3869, or PA14_32840 gene presented a 4-fold increase in NaOCl susceptibility compared to wild-type biofilms. While none of these mutants showed a defect in biofilm formation or attenuated susceptibility of biofilms toward the oxidant hydrogen peroxide (H2O2), all but PA14_32840 also exhibited a 2-4-fold increase in susceptibility toward the antibiotic ciprofloxacin. Further analyses revealed attenuated levels of intracellular ROS and catalase activity only for the apaH and PA1547 mutant, providing insights into the oxidative stress response in P. aeruginosa biofilms. The findings of this paper highlight the complexity of biofilm resistance and the intricate interplay between different mechanisms to survive oxidative stress. Understanding resistance strategies adopted by biofilms is crucial for developing more effective ways to fight resistant bacteria, ultimately contributing to better management of bacterial growth and resistance in clinical and environmental settings.

Recent Trends in Therapeutic Drug Monitoring of Peptide Antibiotics

Antimicrobial peptides take a specific position in the field of antibiotics (ATBs), however, from a large number of available molecules only a few of them were approved and are used in clinics. These therapeutic modalities play a crucial role in the management of diseases caused by multidrug-resistant bacterial pathogens and represent the last-line therapy for bacterial infections. Therefore, there is a demand for a rationale use of such ATBs based on optimization of the dosing strategy to minimize the risk of resistance and ensure the sustainable efficacy of the drug in real clinical practice. Therapeutic drug monitoring, as a measurement of drug concentration in the body fluids or tissues, results in the optimization of the patient´s medication and therapy outcome. This strategy is beneficial and could result in tailored therapy for different types of infection and the prolongation of the use and efficacy of ATBs in hospitals. This review paper provides an actual overview of approved antimicrobial peptides used in clinical practice and covers current trends in their analysis by convenient and advanced methodologies used for their identification and/or quantitation in biological matrices for therapeutic drug monitoring purposes. Special emphasis is given to the methods with perspective clinical outcomes.

Ribosome Assembly and Repair

Ribosomes synthesize protein in all cells. Maintaining both the correct number and composition of ribosomes is critical for protein homeostasis. To address this challenge, cells have evolved intricate quality control mechanisms during assembly to ensure that only correctly matured ribosomes are released into the translating pool. However, these assembly-associated quality control mechanisms do not deal with damage that arises during the ribosomes' exceptionally long lifetimes and might equally compromise their function or lead to reduced ribosome numbers. Recent research has revealed that ribosomes with damaged ribosomal proteins can be repaired by the release of the damaged protein, thereby ensuring ribosome integrity at a fraction of the energetic cost of producing new ribosomes, appropriate for stress conditions. In this article, we cover the types of ribosome damage known so far, and then we review the known repair mechanisms before surveying the literature for possible additional instances of repair.

Mechanistic insights and in vivo efficacy of thiosemicarbazones against methicillin-resistant Staphylococcus aureus

Staphylococcus aureus poses a significant threat in both community and hospital settings due to its infective and pathogenic nature combined with its ability to resist the action of chemotherapeutic agents. Methicillin-resistant S. aureus (MRSA) represents a critical challenge. Metal-chelating thiosemicarbazones (TSCs) have shown promise in combating MRSA and while previous studies hinted at the antimicrobial potential of TSCs, their mechanisms of action against MRSA are still under investigation. We screened a chemical library for anti-staphylococcal compounds and identified a potent molecule named R91 that contained the NNSN structural motif found within TSCs. We identified that R91 and several structural analogs exhibited antimicrobial activity against numerous S. aureus isolates as well as other Gram-positive bacteria. RNAseq analysis revealed that R91 induces copper and oxidative stress responses. Checkerboard assays demonstrated synergy of R91 with copper, nickel, and zinc. Mutation of the SrrAB two-component regulatory system sensitizes S. aureus to R91 killing, further linking the oxidative stress response to R91 resistance. Moreover, R91 was found to induce hydrogen peroxide production, which contributed to its antimicrobial activity. Remarkably, no mutants with elevated R91 resistance were identified, despite extensive attempts. We further demonstrate that R91 can be used to effectively treat an intracellular reservoir of S. aureus in cell culture and can reduce bacterial burdens in a murine skin infection model. Combined, these data position R91 as a potent TSC effective against MRSA and other Gram-positive bacteria, with implications for future therapeutic development.

Targeting the phosphatidylglycerol lipid: An amphiphilic dendrimer as a promising antibacterial candidate

The rapid emergence and spread of multidrug-resistant bacterial pathogens require the development of antibacterial agents that are robustly effective while inducing no toxicity or resistance development. In this context, we designed and synthesized amphiphilic dendrimers as antibacterial candidates. We report the promising potent antibacterial activity shown by the amphiphilic dendrimer AD1b, composed of a long hydrophobic alkyl chain and a tertiary amine-terminated poly(amidoamine) dendron, against a panel of Gram-negative bacteria, including multidrug-resistant Escherichia coli and Acinetobacter baumannii. AD1b exhibited effective activity against drug-resistant bacterial infections in vivo. Mechanistic studies revealed that AD1b targeted the membrane phospholipids phosphatidylglycerol (PG) and cardiolipin (CL), leading to the disruption of the bacterial membrane and proton motive force, metabolic disturbance, leakage of cellular components, and, ultimately, cell death. Together, AD1b that specifically interacts with PG/CL in bacterial membranes supports the use of small amphiphilic dendrimers as a promising strategy to target drug-resistant bacterial pathogens and addresses the global antibiotic crisis.

Merging multi-omics with proteome integral solubility alteration unveils antibiotic mode of action

Antimicrobial resistance is responsible for an alarming number of deaths, estimated at 5 million per year. To combat priority pathogens, like Helicobacter pylori, the development of novel therapies is of utmost importance. Understanding the molecular alterations induced by medications is critical for the design of multi-targeting treatments capable of eradicating the infection and mitigating its pathogenicity. However, the application of bulk omics approaches for unraveling drug molecular mechanisms of action is limited by their inability to discriminate between target-specific modifications and off-target effects. This study introduces a multi-omics method to overcome the existing limitation. For the first time, the Proteome Integral Solubility Alteration (PISA) assay is utilized in bacteria in the PISA-Express format to link proteome solubility with different and potentially immediate responses to drug treatment, enabling us the resolution to understand target-specific modifications and off-target effects. This study introduces a comprehensive method for understanding drug mechanisms and optimizing the development of multi-targeting antimicrobial therapies.

Antioxidant and Pro-Oxidant Properties of Selected Clinically Applied Antibiotics: Therapeutic Insights

BACKGROUND

The balance between antioxidants and pro-oxidants plays a significant role in the context of oxidative stress, influenced by both physiological and non-physiological factors.

OBJECTIVES

In this study, 18 prescribed antibiotics (including doxycycline hydrochloride, tigecycline, rifampicin, tebipenem, cefuroxime, cefixime, potassium clavulanate, colistin, ampicillin, amoxicillin, amikacin, nalidixic acid, azithromycin, pipemidic acid trihydrate, pivmecillinam, aztreonam, fosfomycin sodium, and ciprofloxacin) were subjected to simultaneous determination of antioxidant and pro-oxidant potential to assess if pro-oxidant activity is a dominant co-mechanism of antibacterial activity or if any antibiotic exhibits a balanced effect.

METHODS

This study presents a recently developed approach for the simultaneous assessment of antioxidant and pro-oxidant potential on a single microplate in situ, applied to prescribed antibiotics.

RESULTS

Ten antibiotics from eighteen showed lower antioxidant or pro-oxidant potential, while five exhibited only mild potential with DPPH50 values over 0.5 mM. The pro-oxidant antioxidant balance index (PABI) was also calculated to determine whether antioxidant or pro-oxidant activity was dominant for each antibiotic. Surprisingly, three antibiotics-doxycycline hydrochloride, tigecycline, and rifampicin-showed significant measures of both antioxidant and pro-oxidant activities. Especially notable was tebipenem, a broad-spectrum, orally administered carbapenem, showed a positive PABI index ratio, indicating a dominant antioxidant over pro-oxidant effect.

CONCLUSIONS

These findings could be significant for both therapy, where the antibacterial effect is enhanced by radical scavenging activity, and biotechnology, where substantial pro-oxidant activity might limit microbial viability in cultures and consequently affect yield.

CyuR is a dual regulator for L-cysteine dependent antimicrobial resistance in Escherichia coli

Hydrogen sulfide (H2S), mainly produced from L-cysteine (Cys), renders bacteria highly resistant to oxidative stress and potentially increases antimicrobial resistance (AMR). CyuR is a Cys-dependent transcription regulator, responsible for the activation of the cyuPA operon and generation of H2S. Despite its potential importance, its regulatory network remains poorly understood. In this study, we investigate the roles of the CyuR regulon in a Cys-dependent AMR mechanism in E. coli strains. We show: (1) Generation of H2S from Cys affects the sensitivities to growth inhibitors; (2) Cys supplementation decreases stress responses; (3) CyuR negatively controls the expression of mdlAB encoding a potential transporter for antibiotics; (4) CyuR binds to a DNA sequence motif 'GAAwAAATTGTxGxxATTTsyCC' in the absence of Cys; and (5) CyuR may regulate 25 additional genes which were not reported previously. Collectively, our findings expand the understanding of the biological roles of CyuR relevant to antibiotic resistance associated with Cys.

Reactive Oxygen Species Mediate the Bactericidal Activity of Chlorine Against Salmonella

Chlorine and its derivatives have been used as an antibacterial agent to reduce Salmonella contamination in poultry meat during processing. We evaluated the survival of 4 different Salmonella serotypes (Typhimurium, Enteritidis, Heidelberg, and Gaminara) in the presence of 50 ppm sodium hypochlorite (NaOCl) alone or with the addition of thiourea (radical scavenger) or Dip (iron chelator) to determine the contribution of reactive oxygen species (ROS) in the bactericidal activity of NaOCl. The result showed that for all four serotypes the addition of thiourea or Dip significantly increased the % survival as compared to the respective NaOCl treatment groups, while it was significantly higher with thiourea as compared to Dip (P < 0.05). We also evaluated the survival of 11 deletion mutants of S. Typhimurium, which were demonstrated to increase (∆atpC, ∆cyoA, ∆gnd, ∆nuoG, ∆pta, ∆sdhC, and ∆zwf) or decrease the production of ROS (∆edd, ∆fumB, ∆pykA, and ∆tktB) in Escherichia coli (E. coli), in the presence of 50 ppm. The results showed that only two (∆sdhC and ∆zwf) out of 7 ROS-increasing mutants showed reduced % survival as compared to the wild-type (P < 0.05), while all four deletion ROS-decreasing mutants showed significantly higher % survival as compared to the wild-type (P < 0.05). This work suggests that the production of ROS is a major component of the bactericidal activity of NaOCl against Salmonella serotypes and there might be a significant difference in the metabolic pathways involved in ROS production between Salmonella and E. coli.

Trehalose catalytic shift is an intrinsic factor in Mycobacterium tuberculosis that enhances phenotypic heterogeneity and multidrug resistance

Drug-resistance (DR) in many bacterial pathogens often arises from the repetitive formation of drug-tolerant bacilli, known as persisters. However, it is unclear whether Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis (TB), undergoes a similar phenotypic transition. Recent metabolomics studies have identified that a change in trehalose metabolism is necessary for Mtb to develop persisters and plays a crucial role in metabolic networks of DR-TB strains. The present study used Mtb mutants lacking the trehalose catalytic shift and showed that the mutants exhibited a significantly lower frequency of the emergence of DR mutants compared to wildtype, due to reduced persister formation. The trehalose catalytic shift enables Mtb persisters to survive under bactericidal antibiotics by increasing metabolic heterogeneity and drug tolerance, ultimately leading to development of DR. Intriguingly, rifampicin (RIF)-resistant bacilli exhibit cross-resistance to a second antibiotic, due to a high trehalose catalytic shift activity. This phenomenon explains how the development of multidrug resistance (MDR) is facilitated by the acquisition of RIF resistance. In this context, the heightened risk of MDR-TB in the lineage 4 HN878 W-Beijing strain can be attributed to its greater trehalose catalytic shift. Genetic and pharmacological inactivation of the trehalose catalytic shift significantly reduced persister formation, subsequently decreasing the incidence of MDR-TB in HN878 W-Beijing strain. Collectively, the trehalose catalytic shift serves as an intrinsic factor of Mtb responsible for persister formation, cross-resistance to multiple antibiotics, and the emergence of MDR-TB. This study aids in the discovery of new TB therapeutics by targeting the trehalose catalytic shift of Mtb.

Impact of Conjugation of the Reactive Oxygen Species (ROS)-Generating Catalytic Moiety with Membrane-Active Antimicrobial Peptoids: Promoting Multitarget Mechanism and Enhancing Selectivity

Antimicrobial peptides (AMPs) represent promising therapeutic modalities against multidrug-resistant bacterial infections. As a mimic of natural AMPs, peptidomimetic oligomers like peptoids (i.e., oligo-N-substituted glycines) have been utilized for antimicrobials with resistance against proteolytic degradation. Here, we explore the conjugation of catalytic metal-binding motifs─the amino terminal Cu(II) and Ni(II) binding (ATCUN) motif─with cationic amphipathic antimicrobial peptoids to enhance their efficacy. Upon complexation with Cu(II) or Ni(II), the conjugates catalyzed hydroxyl radical generation, and 22 and 22-Cu exhibited over 10-fold improved selectivity compared to the parent peptoid, likely due to reduced hydrophobicity. Cu-ATCUN-peptoids caused bacterial membrane disruption, aggregation of intracellular biomolecules, DNA oxidation, and lipid peroxidation, promoting multiple killing mechanisms. In a mouse sepsis model, 22 demonstrated antimicrobial and anti-inflammatory efficacy with low toxicity. This study suggests a strategy to improve the potency of membrane-acting antimicrobial peptoids by incorporating ROS-generating motifs, thereby adding oxidative damage as a killing mechanism.

The impact of heat treatment on E. coli cell physiology in rich and minimal media considering oxidative secondary stress

AIMS

This study investigates the cell physiology of thermally injured bacterial cells, with a specific focus on oxidative stress and the repair mechanisms associated with oxidative secondary stress.

METHODS AND RESULTS

We explored the effect of heat treatment on the activity of two protective enzymes, levels of intracellular reactive oxygen species, and redox potential. The findings reveal that enzyme activity slightly increased after heat treatment, gradually returning to baseline levels during subculture. The response of Escherichia coli cells to heat treatment, as assessed by the level of superoxide radicals generated and redox potential, varied based on growth conditions, namely minimal and rich media. Notably, the viability of injured cells improved when antioxidants were added to agar media, even in the presence of metabolic inhibitors.

CONCLUSIONS

These results suggest a complex system involved in repairing damage in heat-treated cells, particularly in rich media. While repairing membrane damage is crucial for cell regrowth and the electron transport system plays a critical role in the recovery process of injured cells under both tested conditions.

Stalled ribosome rescue factors exert different roles depending on types of antibiotics in Escherichia coli

Escherichia coli possesses three stalled-ribosome rescue factors, tmRNA·SmpB (primary factor), ArfA (alternative factor to tmRNA·SmpB), and ArfB. Here, we examined the susceptibility of rescue factor-deficient strains from E. coli SE15 to various ribosome-targeting antibiotics. Aminoglycosides specifically decreased the growth of the ΔssrA (tmRNA gene) strain, in which the levels of reactive oxygen species were elevated. The decrease in growth of ΔssrA could not be complemented by plasmid-borne expression of arfA, arfB, or ssrAAA to DD mutant gene possessing a proteolysis-resistant tag sequence. These results highlight the significance of tmRNA·SmpB-mediated proteolysis during growth under aminoglycoside stress. In contrast, tetracyclines or amphenicols decreased the growth of the ΔarfA strain despite the presence of tmRNA·SmpB. Quantitative RT-PCR revealed that tetracyclines and amphenicols, but not aminoglycosides, considerably induced mRNA expression of arfA. These findings indicate that tmRNA·SmpB, and ArfA exert differing functions during stalled-ribosome rescue depending on the type of ribosome-targeting antibiotic.

Reversal of carbapenem resistance in Pseudomonas aeruginosa by camelid single domain antibody fragment (VHH) against the C4-dicarboxylate transporter

Antimicrobial resistance is emerging as the new healthcare crisis necessitating the development of newer classes of drugs using non-traditional approaches. Pseudomonas aeruginosa, one of the most common pathogens involved in nosocomial infections, is extremely difficult to treat even with the last resort frontline drug, the carbapenems. As the pathogen has the ability to acquire resistance to new small-molecule antibiotics, being deployed, a novel biological approach has been tried using antibody fragments in combination with carbapenems and β-lactams as adjunct therapy for an enduring solution to the problem. In this study, we developed a camelid antibody fragment (VHH) library against P. aeruginosa and isolated a highly potent hit, PsC23. Mass spectrometry identified the target to be a component of the C4-dicarboxylate transporter that feeds metabolites to the glyoxylate shunt particularly under conditions of oxidative stress. PsC23 is bacteriostatic at a concentration of 1.66 µM (25 µg ml-1) and shows a synergistic effect with both the classes of drugs at an effective concentration of 100-200 nM (1.5-3.0 µg ml-1) when co administered with them. In combination with meropenem the VHH completely cleared the infection from a neutropenic mouse with a carbapenem-resistant P. aeruginosa systemic infection. Blocking the glyoxylate shunt by PsC23 resulted in disruption of energy transduction due to a respiratory shift to the oxygen-depleted TCA cycle causing inhibition of efflux and increased free radical generation from carbapenems and β-lactams exerting a strong bactericidal effect that reversed the resistance to multiple unrelated drugs.

Development of an effective meropenem/KPC-2 inhibitor combination to combat infections caused by carbapenem-resistant Klebsiella pneumoniae

The global public health threat of antibiotic resistance continues to escalate, and necessitates the implementation of urgent measures to expand the arsenal of antimicrobial drugs. This study identified a benzoxaborane compound, namely 5-chloro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2178), which can inhibit the catalytic activity of the Klebsiella pneumoniae carbapenemase (KPC-2) enzyme effectively. The efficacy of AN2718 as an inhibitor for the KPC-2 enzyme was verified through various assays, including enzyme activity assays and isothermal titration calorimetry. Results of multiple biochemical assays, minimum inhibitory concentration assays and time-killing assays also showed that binding of AN2718 to KPC-2 enabled restoration of the bactericidal effect of meropenem. The survival rate of mice infected with carbapenem-resistant, high-virulence strains increased significantly upon treatment with AN2718. Most importantly, the meropenem and AN2718 combination was effective on KPC-2 mutations such as KPC-33, which evolved clinically and exhibited resistance to ceftazidime-avibactam after clinical use for a couple of years. Comprehensive safety tests both in vitro and in vivo, such as cytotoxicity, haemolytic activity and cytochrome P450 inhibition assays, demonstrated that AN2718 was safe for clinical use. These promising data indicate that AN2718 has high potential for approval for the treatment of drug resistant-bacterial infections, including those caused by ceftazidime-avibactam-resistant strains. AN2718 can be regarded as a valuable addition to the current antimicrobial armamentarium, and a promising tool to combat antimicrobial resistance.

Escaping the ESKAPE pathogens: A review on antibiofilm potential of nanoparticles

ESKAPE pathogens, a notorious consortium comprising Enterococcusfaecium, Staphylococcusaureus, Klebsiellapneumoniae, Acinetobacterbaumannii, Pseudomonasaeruginosa, and Enterobacter species, pose formidable challenges in healthcare settings due to their multidrug-resistant nature. The increasing global cases of antimicrobial-resistant ESKAPE pathogens are closely related to their remarkable ability to form biofilms. Thus, understanding the unique mechanisms of antimicrobial resistance of ESKAPE pathogens and the innate resilience of biofilms against traditional antimicrobial agents is important for developing innovative strategies to establish effective control methods against them. This review offers a thorough analysis of biofilm dynamics, with a focus on the general mechanisms of biofilm formation, the significant contribution of persister cells in the resistance mechanisms, and the recurrence of biofilms in comparison to planktonic cells. Additionally, this review highlights the potential strategies of nanoparticles for managing biofilms in the ESKAPE group of pathogens. Nanoparticles, with their unique physicochemical properties, provide promising opportunities for disrupting biofilm structures and improving antimicrobial effectiveness. The review has explored interactions between nanoparticles and biofilms, covering a range of nanoparticle types such as metal, metal-oxide, surface-modified, and functionalized nanoparticles, along with organic nanoparticles and nanomaterials. The additional focus of this review also encompasses green synthesis techniques of nanoparticles that involve plant extract and supernatants from bacterial and fungal cultures as reducing agents. Furthermore, the use of nanocomposites and nano emulsions in biofilm management of ESKAPE is also discussed. To conclude, the review addresses the current obstacles and future outlooks in nanoparticle-based biofilm management, stressing the necessity for further research and development to fully exploit the potential of nanoparticles in addressing biofilm-related challenges.

Staphylococcus aureus SOS response: Activation, impact, and drug targets

Staphylococcus aureus is a common cause of diverse infections, ranging from superficial to invasive, affecting both humans and animals. The widespread use of antibiotics in clinical treatments has led to the emergence of antibiotic-resistant strains and small colony variants. This surge presents a significant challenge in eliminating infections and undermines the efficacy of available treatments. The bacterial Save Our Souls (SOS) response, triggered by genotoxic stressors, encompasses host immune defenses and antibiotics, playing a crucial role in bacterial survival, invasiveness, virulence, and drug resistance. Accumulating evidence underscores the pivotal role of the SOS response system in the pathogenicity of S. aureus. Inhibiting this system offers a promising approach for effective bactericidal treatments and curbing the evolution of antimicrobial resistance. Here, we provide a comprehensive review of the activation, impact, and key proteins associated with the SOS response in S. aureus. Additionally, perspectives on therapeutic strategies targeting the SOS response for S. aureus, both individually and in combination with traditional antibiotics are proposed.

Transforming Spirulina maxima Biomass into Ultrathin Bioactive Coatings Using an Atmospheric Plasma Jet: A New Approach to Healing of Infected Wounds

The challenge of wound healing, particularly in patients with comorbidities such as diabetes, is intensified by wound infection and the accelerating problem of bacterial resistance to current remedies such as antibiotics and silver. One promising approach harnesses the bioactive and antibacterial compound C-phycocyanin from the microalga Spirulina maxima. However, the current processes of extracting this compound and developing coatings are unsustainable and difficult to achieve. To circumvent these obstacles, a novel, sustainable argon atmospheric plasma jet (Ar-APJ) technology that transforms S. maxima biomass into bioactive coatings is presented. This Ar-APJ can selectively disrupt the cell walls of S. maxima, converting them into bioactive ultrathin coatings, which are found to be durable under aqueous conditions. The findings demonstrate that Ar-APJ-transformed bioactive coatings show better antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. Moreover, these coatings exhibit compatibility with macrophages, induce an anti-inflammatory response by reducing interleukin 6 production, and promote cell migration in keratinocytes. This study offers an innovative, single-step, sustainable technology for transforming microalgae into bioactive coatings. The approach reported here has immense potential for the generation of bioactive coatings for combating wound infections and may offer a significant advance in wound care research and application.