Bacterial Resistance Mechanisms Research Articles

A study on the antibacterial activity and antimicrobial resistance of pyridinium cationic pillar[5]arene against Staphylococcus aureus and Escherichia coli.

An increasing number of infections caused by multidrug-resistant (MDR) Staphylococcus aureus （S. aureus） and Escherichia coli （E. coli） have severely affected human society. Thus, it is essential to develop an alternative type of antibacterial agents that has a different bacterial resistance mechanism from that of traditional antibiotics. After the synthesis and structural characterization of a cationic pillar[5]arene with pyridinium groups (PP5), the antibacterial and antibiofilm activities as well as its microbial resistance were systematically investigated. In-depth evaluation of biological studies revealed that PP5 was an active antibacterial agent, with surprising antibiofilm formation ability against E. coli and S. aureus. From the results of differential scanning calorimetry and transmission electron microscopy, it was concluded that the microbicidal activity of PP5 was due to the physical disruption of the pathogen's membrane and the subsequent leakage of cytoplasmic components, which could greatly reduce the rapid generation of resistance. It was presented that the easily available PP5 has high activity to inhibit Gram-positive and Gram-negative bacteria and/or their biofilms with low cytotoxicity. This pillar[5]arene derivative can be used as a good candidate for controlling drug-resistant pathogenic bacterial infections and treating MDR bacteria.

Concordance of the filmarray blood culture identification panel 2 and classical microbiological methods in a bacteriemia diagnostic unit

Our study evaluates the effectiveness of the FilmArray Blood Culture Identification Panel 2 in a rapid bacteremia diagnostic system, using bacteriological culture as a reference. A total of 2042 positive blood cultures were analyzed, the FilmArray was performed for 175. Concordance was higher in monomicrobial bacteremia (95%) than in polymicrobial bacteremia's (72.2%). For detecting bacterial resistance mechanisms, concordance was very high (100% for Gram-positive bacteria and 98.12% for Gram-negative). This methodology provides significant improvements in response time and is especially useful for the detection of monomicrobial bacteremia.

EGCG-coated silver nanoparticles self-assemble with selenium nanowires for treatment of drug-resistant bacterial infections by generating ROS and disrupting biofilms

Bacterial infections pose a serious threat to human health, and the development of new antibiotics has not kept pace with the development of bacterial resistance. Therefore, there is an urgent need to design antibiotic-like nano-formulations that break through bacterial resistance mechanisms. In this work, we successfully synthesized a safe and effective antibacterial nano-formulation of Se@Ag@EGCG by self-assembly of epigallocatechin gallate (EGCG)-coated silver nanoparticles (Ag) on the surface of selenium nanowires (Se). The in vitro bacteriostatic results showed that 40 μg ml−1 Se@Ag@EGCG had significant antibacterial activity against drug-resistant Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by destroying the formation of bacterial biofilm, promoting the production of high concentration reactive oxygen species and destroying bacterial cell wall. In addition, the results of in vivo antibacterial experiments showed that subcutaneous administration of 10 mg kg−1 of Se@Ag@EGCG could promote wound healing by reducing apoptosis and inflammatory responses in infected wounds. It is worth mentioning that the reduced and modified Se@Ag@EGCG by this natural product has negligible in vivo toxicity. This development strategy of nano-antibacterial materials, which breaks through the drug resistance mechanism, provides new ideas for the development of drugs for drug-resistant bacterial infections.

Trimethylamine N-Oxide Reduces the Susceptibility of Escherichia coli to Multiple Antibiotics.

Trimethylamine N-oxide (TMAO), an important intestinal flora-derived metabolite, plays a role in the development of cardiovascular disease and tumor immunity. Here, we determined the minimum inhibitory concentration (MIC) of antibiotics against Escherichia coli under gradient concentrations of TMAO and performed a bacterial killing analysis. Overall, TMAO (in the range of 10 ~ 100 mM) increased the MIC of quinolones, aminoglycosides, and β-lactams in a concentration-dependent manner, and increased the lethal dose of antibiotics against E. coli. It implies that TMAO is a potential risk for failure of anti-infective therapy, and presents a case for the relationship between intestinal flora-derived metabolites and antibiotic resistance. Further data demonstrated that the inhibition of antibiotic efficacy by TMAO is independent of the downstream metabolic processes of TMAO and the typical bacterial resistance mechanisms (mar motif and efflux pump). Interestingly, TMAO protects E. coli from high-protein denaturant (urea) stress and improves the viability of bacteria following treatment with two disinfectants (ethanol and hydrogen peroxide) that mediate protein denaturation by chemical action or oxidation. Since antibiotics can induce protein inactivation directly or indirectly, our work suggests that disruption of protein homeostasis may be a common pathway for different stress-mediated bacterial growth inhibition/cell death. In addition, we further discuss this possibility, which provides a different perspective to address the global public health problem of antibiotic resistance.

Use of amoxicillin/sulbactam/trifamox in acute bacterial sinusitis

The most common mechanism of bacterial resistance accounting for about 80% of all cases is the enzymatic cleavage of the antibiotic. Enzymes that destroy β-lactam antibiotics are called β-lactamases. They destroy the amide bond in the β-lactam ring of β-lactam antibiotics, which manifests itself as the absence of the result of the action of antibiotics. The use of β-lactamase inhibitors (clavulanic acid, sulbactam and tazobactam) allows maintaining the benefits of long-known efficient antibiotics. Based on the β-lactam structure, they have a high affinity for β-lactamases and, as a result of a complex physicochemical process, form stable inactive complexes with these enzymes (β-lactamases suicide inhibitor). Under the influence of β-lactamases produced by bacteria, they are not hydrolyzed, like amoxicillin, but are firmly bound to them, protecting amoxicillin from hydrolysis. The use of Trifamox in modern antibiotic therapy is relevant not only in the hospital, but also on an outpatient basis, with recurrent diseases that are not amenable to treatment with conventional β-lactams.

Patrones de resistencia a antibióticos en infecciones asociadas a la atención de salud en un centro de tercer nivel con reconversión hospitalaria en la pandemia por COVID-19

Objetive: Description of the different isolated microorganisms and their prevalence in infections associated with health care, in addition to determining their patterns of resistance to antibiotics in patients admitted with a confirmed or suspected diagnosis of COVID-19 in the Intensive Care Unit, during a third-level medical center with hospital reconversion. Method: Patient demographic data was obtained from the clinical record, with defined criteria. Antibiotic resistance patterns were evaluated as well as the identification of isolated bacteria in cultures of expectoration, pleural fluid, catheter tips. For bacterial identification and resistance mechanisms, automated equipment and phenotypic tests were used, following the CLSI (Clinical & Laboratory Standards Institute) criteria. Results: A total of 100 patients with bacterial infection added to the main COVID-19 picture were obtained, representing pneumonia, urinary tract infection, catheter infections and bacteremia. A total of 100 strains were isolated, of which 84 are Extremely Drug Resistant, 12 Multidrug Resistant and only 4 variable sensitivity. The bacteria with the highest prevalence is Staphylococcus aureus with, followed by Pseudonomas aeruginosa and Stenotrophomonas maltophilia. 100% of the patients admitted to the ICU (Intensive Care Unit) had death. Conclusion: The increase in resistance to antibiotics in the COVID-19 pandemic has set off alarms due to the complication that this brings, and the improper use of drugs as prophylaxis or attempted treatment only generates selective pressure that leads to an increase in resistance as observed in the isolated strains in this study, where the vast majority present enzymes as well as other resistance mechanisms that confer them to be XDR (Extremely Drug Resistant).

Interplay between the Enamine and Imine Forms of the Hydrolyzed Imipenem in the Active Sites of Metallo-β-lactamases and in Water Solution.

Deactivation of the β-lactam antibiotics in the active sites of the β-lactamases is among the main mechanisms of bacterial antibiotic resistance. As drugs of last resort, carbapenems are efficiently hydrolyzed by metallo-β-lactamases, presenting a serious threat to human health. Our study reveals mechanistic aspects of the imipenem hydrolysis by bizinc metallo-β-lactamases, NDM-1 and L1, belonging to the B1 and the B3 subclasses, respectively. The results of QM(PBE0-D3/6-31G**)/MM simulations show that the enamine product with the protonated nitrogen atom is formed as the major product in NDM-1 and as the only product in the L1 active site. In NDM-1, there is also another reaction pathway that leads to the formation of the (S)-enantiomer of the imine form of the hydrolyzed imipenem; this process occurs with the higher energy barriers. The absence of the second pathway in L1 is due to the different amino acid composition of the active site loop. In L1, the hydrophobic Pro226 residue is located above the pyrroline ring of imipenem that blocks protonation of the carbon atom. Electron density analysis is performed at the stationary points to compare reaction pathways in L1 and NDM-1. Tautomerization from the enamine to the imine form likely happens in solution after the dissociation of the hydrolyzed imipenem from the active site of the enzyme. Classical molecular dynamics simulations of the hydrolyzed imipenem in solution, both with the neutral enamine and the negatively charged N-C2-C3 fragment, demonstrate a huge diversity of conformations. The vast majority of conformations blocks the C3-atom from the side required for the (S)-imine formation upon tautomerization. Thus, according to our calculations, formation of the (R)-imine is more likely. QM(PBE0-D3/6-31G**)/MM molecular dynamics simulations of the hydrolyzed imipenem with the negatively charged N-C2-C3 fragment followed by the Laplacian bond order analysis demonstrate that the N═C2-C3- resonance structure is the most pronounced that facilitates formation of the imine form. The proposed mechanism of the enzymatic enamine formation and its subsequent tautomerization to the imine form in solution is in agreement with the recent spectroscopic and NMR studies.

Temporal dynamics of antibiotic resistant bacteria and antibiotic resistance genes in activated sludge upon exposure to starvation

The activated sludge represents a huge reservoir for antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Owing to the wastewater fluctuation, annual maintenance and storage requirement, the activated sludge in wastewater treatment plants (WWTPs) may suffer from substrate deficiency (i.e., starvation). Whereas the starvation has been confirmed to regulate the antibiotic resistance in numerous pure bacteria, its impacts on the antibiotic resistance in activated sludge remain unclear. Here, the dynamics of sulfonamide and tetracycline ARB and corresponding ARGs in three forms including intracellular ARGs (iARGs), adsorbed extracellular ARGs (aeARGs) and free extracellular ARGs (feARGs) in activated sludge upon exposure to starvation were investigated. The results showed that, among the different electron donors (i.e., carbon, nitrogen and phosphate), carbon starvation could effectively reduce the absolute abundance of ARB and aeARGs by up to 1.68 lgs and 2.62 lgs, respectively, and released a small amount of feARGs in wastewater with the maximum value of 1.1 × 105 copies/mL due to the high degree of sludge cell lysis and DNA adsorption/degradation. For the different acceptor conditions (that is, alternating anaerobic-aerobic, anaerobic, anoxic and aerobic), the anaerobic-aerobic starvation obviously mitigated the absolute abundance of ARB, aeARGs and iARGs by 0.71 lgs, 3.41 lgs and 1.35 lgs, respectively, via the substantial sludge cell lysis and DNA degradation. These findings demonstrated the response patterns and mechanisms of bacterial resistance in activated sludge to starvation stress, and thus provide clues to control the risk of antibiotic resistance in WWTPs by the starvation strategy.

Quantitative Proteomics Reveals That the Protein Components of Outer Membrane Vesicles (OMVs) in Aeromonas hydrophila Play Protective Roles in Antibiotic Resistance.

In recent years, the intracellular mechanisms that contribute to antibiotic resistance have received increasing attention, and outer membrane vesicles (OMVs) have been reported to be related to antibiotic resistance in several Gram-negative bacterial species. However, the intrinsic molecular mechanisms and the form of such antibiotic resistance are still largely unknown. In this study, OMVs from an oxytetracycline (OXY) sensitive aquatic pathogen, Aeromonas hydrophila (OXY-S), were found with significantly increased OXY resistance. Interestingly, the OXY-resistant strain (OXY-R) had a more protective role in OXY resistance. Therefore, a DIA-based quantitative proteomics analysis was performed to compare the differential expression of OMV proteins between OXY-R (OMVsR) and OXY-S (OMVsS). The results showed that seven proteins increased and five proteins decreased in OMVsR vs OMVsS. A subsequent antibiotics susceptibility assay showed that the deletion of icd, rpsF, and iscS significantly increased OXY sensitivity. Moreover, the exogenous addition of the crude OMV fractions of overexpressed recombinant proteins in E.coli with rRpsF, rIcd, rIscS, rOmpA, rPepA, rFrdA, and rRplQ demonstrated that these proteins promoted the OXY resistance of A.hydrophila. Overall, our results indicate the important protective role of OMVs in antibiotic resistance in A.hydrophila and provide novel insights on bacterial antibiotic resistance mechanisms.

The Integration of Proteomics and Metabolomics Data Paving the Way for a Better Understanding of the Mechanisms Underlying Microbial Acquired Drug Resistance.

Due to an increase in the overuse of antimicrobials and accelerated incidence of drug resistant pathogens, antimicrobial resistance has become a global health threat. In particular, bacterial antimicrobial resistance, in both hospital and community acquired transmission, have been found to be the leading cause of death due to infectious diseases. Understanding the mechanisms of bacterial drug resistance is of clinical significance irrespective of hospital or community acquired since it plays an important role in the treatment strategy and controlling infectious diseases. Here we highlight the advances in mass spectrometry-based proteomics impact in bacterial proteomics and metabolomics analysis- focus on bacterial drug resistance. Advances in omics technologies over the last few decades now allows multi-omics studies in order to obtain a comprehensive understanding of the biochemical alterations of pathogenic bacteria in the context of antibiotic exposure, identify novel biomarkers to develop new drug targets, develop time-effectively screen for drug susceptibility or resistance using proteomics and metabolomics.

Detection of Metallo b-Lactamases in Clinical Isolates of Pseudomonas aeruginosa in a Tertiary Care Hospital

Background: Pseudomonas aeruginosa are among the major nosocomial pathogens that demonstrate all known enzymatic and mutational mechanism of bacterial resistance. They are able to acquire drug resistant determinants by horizontal transfer of mobile genetic elements coding for class B carbapenemases, called metallo b lactamases which hydrolyze all b lactams except aztreonam. MBLs like bla VIM has been reported among isolates of Enterobacteriaceae family, P.aeruginosa and other gram negative nonfermenters. On the other hand NDM-1 was first identified in Klebsiella Pneumoniae. Its spread among Pseudomonaceae implies possibility of numerous New NDM-1 cases to be detected in near future.
 Objective: The study aimed to isolate VIM and NDM-1 producing P. aeruginosa from burn wound and to see their susceptibility pattern.
 Materials and methods: P. aeruginosa was isolated by culturing on Macconkey agar media both on 370 C and 420 C and biochemical test. For gene detection organisms were stored at -700C, bla VIM and bla NDM-1 was detected by PCR. Susceptibility pattern of organisms were done by Kirby Bauer Disc Diffusion Method.
 Result: Among the 98 isolated P. aeruginosa 21(47.7%) were VIM producers and 6 (13.6%) NDM-1 producers. VIM producers were 80.9% resistant to imipenem and NDM-1 producers were 100% resistant imipenem.
 Discussion: VIM producing P. aeruginosa was isolated from burn patient in accordance with other study, NDM-1 producing P. aeruginosa is emerging that are more resistant to conventional antibiotcs even to the last resort drug imipenem.
 Conclusion: Imipenem resistence is increasing among P. aeruginosa as a result of acquiring MBL genes. Risk factors for acquiring resistance is increased carbapenem use, longer hospital stay, ICU admission, being on total parenteral nutrition, using catheter and tubes. In this study patient in whom imipenem resistant isolates were identified had hospital stay more than 7 days
 Sir Salimullah Med Coll J 2022; 30: 35-39

Microbiological, Clinical, and PK/PD Features of the New Anti-Gram-Negative Antibiotics: β-Lactam/β-Lactamase Inhibitors in Combination and Cefiderocol-An All-Inclusive Guide for Clinicians.

Bacterial resistance mechanisms are continuously and rapidly evolving. This is particularly true for Gram-negative bacteria. Over the last decade, the strategy to develop new β-lactam/β-lactamase inhibitors (BLs/BLIs) combinations has paid off and results from phase 3 and real-world studies are becoming available for several compounds. Cefiderocol warrants a separate discussion for its peculiar mechanism of action. Considering the complexity of summarizing and integrating the emerging literature data of clinical outcomes, microbiological mechanisms, and pharmacokinetic/pharmacodynamic properties of the new BL/BLI and cefiderocol, we aimed to provide an overview of data on the following compounds: aztreonam/avibactam, cefepime/enmetazobactam, cefepime/taniborbactam, cefepime/zidebactam, cefiderocol, ceftaroline/avibactam, ceftolozane/tazobactam, ceftazidime/avibactam, imipenem/relebactam, meropenem/nacubactam and meropenem/vaborbactam. Each compound is described in a dedicated section by experts in infectious diseases, microbiology, and pharmacology, with tables providing at-a-glance information.

Antibacterial Activity of Antimicrobial Peptide Indolicidin against Multidrug-Resistant Klebseilla pneumoniae Isolated from Patients with Burns

The emergence of multidrug resistant Klebsiella pneumoniae has become a significant problem worldwide and also being a major threat to patients with burns infections. The therapeutic action of antimicrobial peptides derived from humans or animals or synthetic peptides attracted attention as alternatives for antibiotics in order to treat the resistant strains especially with strains isolated from burn patients. The current study investigated the role of antimicrobial peptide Indolicidin as an antibacterial agent with multidrug K. pneumonia isolates from burns. The collection of study samples has taken place at the period between November 2020 and completed at end of March 2021, it has included 250 clinical specimens as burn swabs from inpatients with burn infections admitted in four hospitals in Baghdad. The results of selective media, biochemical tests, and Vitek2 system identified 40 isolates (16%) as K. pneumoniae from all collected bacterial cultures. The results of the antimicrobial susceptibility test by using the disc diffusion method for the isolates under study showed that K. pneumoniae clinical isolates were moderate resistant to the majority of the antibiotics tested. The majority of K. pneumoniae isolates were high resistant to Erythromycin (100%) and Ceftazidime (85%), also, it was obvious resistance to Ceftriaxone, Cefepime and Cefotaxime, while the lowest percentage of resistance was for Impenem (25%) and Meropenem (38%). The results of minimum inhibitory concentrations (MICs) of indolicidine against (10) K. pneumoniae isolates which multidrug resistant and formed the strong biofilm, revealed that range of concentrations of indolicidin was (0.7-100 µg/ml) and it was obvious that there is a significant effect of indolicdin on the growth of K. pneumoniae at very low concentrations. In this study, we believe that the development of these antimicrobial peptides may become a new generation of urgently needed antimicrobials that can overcome bacterial resistance mechanisms.

Multiplex Digital Quantification of β-Lactamase Genes in Antibiotic-Resistant Bacteria by Counting Gold Nanoparticle Labels on Silicon Microchips.

Digital quantification based on counting of individual molecules is a promising approach for different biomedical applications due to its enhanced sensitivity. Here, we present a method for the digital detection of nucleic acids (DNA and RNA) on silicon microchips based on the counting of gold nanoparticles (GNPs) in DNA duplexes by scanning electron microscopy (SEM). Biotin-labeled DNA is hybridized with capture oligonucleotide probes immobilized on the microchips. Then biotin is revealed by a streptavidin–GNP conjugate followed by the detection of GNPs. Sharp images of each nanoparticle allow the visualization of hybridization results on a single-molecule level. The technique was shown to provide highly sensitive quantification of both short oligonucleotide and long double-strand DNA sequences up to 800 bp. The lowest limit of detection of 0.04 pM was determined for short 19-mer oligonucleotide. The method’s applicability was demonstrated for the multiplex quantification of several β-lactamase genes responsible for the development of bacterial resistance against β-lactam antibiotics. Determination of nucleic acids is effective for both specific DNA in lysates and mRNA in transcripts. The method is also characterized by high selectivity for single-nucleotide polymorphism discrimination. The proposed principle of digital quantification is a perspective for studying the mechanisms of bacterial antibiotic resistance and bacterial response to drugs.

Pharmacological activities of allylbenzene and allylanisole phenylpropanoids: Inhibition of antibiotic resistance targets and toxicity profile in a Drosophila melanogaster model

IntroductionThe rapid emergence of multidrug-resistant bacteria has demanded the discovery of new drugs capable of inhibiting bacterial resistance mechanisms, such as those mediated by efflux proteins and β-lactamases. ObjectiveConsidering the evidence indicating that phenylpropanoids are effective substances against bacterial resistance, the present study aimed to evaluate the antibacterial activity of compounds allylbenzene and allylanisol against the Staphylococcus aureus strain SA-K4414, which carries genes encoding the β-lactamase and QacA/B proteins. MethodsThe Minimum Inhibitory Concentrations (MICs) were determined by the broth microdilution method. The expression of β-lactamase was verified through the association of the inhibitor sulbactam with the antibiotic ampicillin, while its inhibition was analyzed through the reduction of the penicillin MIC in the presence of phenolic compounds. The efflux pump inhibition was analyzed by the reduction in the MIC of the pump substrate ethidium bromide. The toxicity against Drosophila melanogaster was assessed by evaluating mortality and negative geotaxis through the fumigation method. ResultsThe results demonstrated that the phenylpropanoids failed to show relevant direct antibacterial activity, with MIC values above 1024 µg/mL. The association of allylbenzene and allylanisole with penicillin potentiated its antibacterial effect, reducing the antibiotic MIC (512 µg/mL) to 128 µg/mL and 256 µg/mL, respectively. The compounds also reduced the MIC of EtBr, indicating a possible inhibitory effect against the β-lactamase enzyme and the QacA/B efflux protein. Regarding toxicity, allylbenzene (after 12 h) and allylanisole (after 3 h) presented EC50 of 19.21 μL/mL and 11.07 μL/mL, respectively. These compounds also caused damage to the locomotor system of flies, which was potentiated following increasing concentrations and exposure period. ConclusionIt is concluded that the compounds allylbenzene and allylanisole can inhibit the resistance mechanisms mediated by the β-lactamase enzyme and the efflux protein QacA/B. However, due to the significant toxicity observed, further research is required to assess the safety of these compounds.

Restoration of antibacterial activity of inactive antibiotics via combined treatment with a cyanographene/Ag nanohybrid

The number of antibiotic-resistant bacterial strains is increasing due to the excessive and inappropriate use of antibiotics, which are therefore becoming ineffective. Here, we report an effective way of enhancing and restoring the antibacterial activity of inactive antibiotics by applying them together with a cyanographene/Ag nanohybrid, a nanomaterial that is applied for the first time for restoring the antibacterial activity of antibiotics. The cyanographene/Ag nanohybrid was synthesized by chemical reduction of a precursor material in which silver cations are coordinated on a cyanographene sheet. The antibacterial efficiency of the combined treatment was evaluated by determining fractional inhibitory concentrations (FIC) for antibiotics with different modes of action (gentamicin, ceftazidime, ciprofloxacin, and colistin) against the strains Escherichia coli, Pseudomonas aeruginosa, and Enterobacter kobei with different resistance mechanisms. Synergistic and partial synergistic effects against multiresistant strains were demonstrated for all of these antibiotics except ciprofloxacin, which exhibited an additive effect. The lowest average FICs equal to 0.29 and 0.39 were obtained for colistin against E. kobei and for gentamicin against E. coli, respectively. More importantly, we have experimentally confirmed for the first time, that interaction between the antibiotic's mode of action and the mechanism of bacterial resistance strongly influenced the combined treatment’s efficacy.

Poly-Gamma-Glutamic Acid Secretion Protects Bacillus subtilis from Zinc and Copper Intoxication.

ABSTRACTZinc and copper are essential micronutrients that serve as a cofactors for numerous enzymes. However, when present at elevated concentrations, zinc and copper are highly toxic to bacteria. To combat the effects of zinc and copper excess, bacteria have evolved a wide array of defense mechanisms. Here, we show that the Gram-positive soil bacterium, Bacillus subtilis, produces the extracellular polymeric substance, poly-gamma-glutamate (γ-PGA) as a protective mechanism in response to zinc and copper excess. Furthermore, we provide evidence that zinc and copper dependent γ-PGA production is independent of the DegS-DegQ two-component regulatory system and likely occurs at a posttranscriptional level through the small protein, PgsE. These data provide new insight into bacterial metal resistance mechanisms and contribute to our understanding of the regulation of bacterial γ-PGA biosynthesis.IMPORTANCE Zinc and copper are potent antimicrobial compounds. As such, bacteria have evolved a diverse range of tools to prevent metal intoxication. Here, we show that the Gram-positive model organism, Bacillus subtilis, produces poly-gamma-glutamic acid (γ-PGA) as a protective mechanism against zinc and copper intoxication and that zinc and copper dependent γ-PGA production occurs by a yet undefined mechanism independent of known γ-PGA regulation pathways.

Antibacterial nanomaterials: Upcoming hope to overcome antibiotic resistance crisis

Abstract When combined with nanomaterials, antibiotics show antibacterial activity against susceptible and resistant bacterial strains at significantly lower concentrations. Unfortunately, to date, no research study has examined the effect of the antibiotic mode of action and mechanism of bacterial resistance on the effectiveness of combined antibacterial treatment with nanomaterials. Therefore, in this review, we performed a thorough analysis and critical evaluation of previously published data related to the combined antibacterial effect of antibiotics with nanostructured materials with a targeted focus on relationships between antibiotic’s modes of action and bacterial resistance mechanisms for relevant nanomaterials and their impact on the resulting synergistic effects. Following thorough data analysis and critical discussion, we have discovered and are the first who present that antibiotic’s mode of action and bacterial resistance mechanism determine the final effectiveness of combined antibacterial treatment with nanomaterials. We therefore conclude that only certain combinations of nanomaterials with antibiotics can lead to the enhancement and restoration of the antibacterial effectiveness of antibiotics against certain resistant bacteria. Moreover, the recently occurring development of bacterial resistance towards nanomaterials is also discussed together with a possibility of how to prevent it. All discovered findings provide a new view and perspective on this issue helping to navigate further approaches to combat the antibiotic crisis.

Extracellular vesicles as an alternative copper-secretion mechanism in bacteria

Metal homeostasis is fundamental for optimal performance of cell metabolic pathways. Over the course of evolution, several systems emerged to warrant an intracellular metal equilibrium. When exposed to growth-challenging copper concentrations, Gram-negative bacteria quickly activate copper-detoxification mechanisms, dependent on transmembrane-protein complexes and metallochaperones that mediate metal efflux. Here, we show that vesiculation is also a common bacterial response mechanism to high copper concentrations, and that extracellular vesicles (EVs) play a role in transporting copper. We present evidence that bacteria from different ecological niches release copious amounts of EVs when exposed to copper. Along with the activation of the classical detoxification systems, we demonstrate that copper-stressed cells of the cyanobacterium Synechocystis sp. PCC6803 release EVs loaded with the copper-binding metallochaperone CopM. Under standard growth conditions, CopM-loaded EVs could also be isolated from a Synechocystis strain lacking a functional TolC-protein, which we characterize here as exhibiting a copper-sensitive phenotype. Analyses of Synechocystis tolC-mutant’s EVs isolated from cells cultivated under standard conditions indicated the presence of copper therein, in significantly higher levels as compared to those from the wild-type. Altogether, these results suggest that release of EVs in bacteria represent a novel copper-secretion mechanism, shedding light into alternative mechanisms of bacterial metal resistance.

Antibiotic Combination Therapy: A Strategy to Overcome Bacterial Resistance to Aminoglycoside Antibiotics.

After the first aminoglycoside antibiotic streptomycin being applied in clinical practice in the mid-1940s, aminoglycoside antibiotics (AGAs) are widely used to treat clinical bacterial infections and bacterial resistance to AGAs is increasing. The bacterial resistance to AGAs is owed to aminoglycoside modifying enzyme modification, active efflux pump gene overexpression and 16S rRNA ribosomal subunit methylation, leading to modification of AGAs’ structures and decreased concentration of drugs within bacteria. As AGAs’s side effects and bacterial resistance, the development of AGAs is time-consuming and difficult. Because bacterial resistance may occur in a short time after application in clinical practice, it was found that the antibacterial effect of the combination was not only better than that of AGAs alone but also reduce the dosage of antibiotics, thereby reducing the occurrence of side effects. This article reviews the clinical use of AGAs, the antibacterial mechanisms, the molecular mechanisms of bacterial resistance, and especially focuses a recent development of the combination of AGAs with other drugs to exert a synergistic antibacterial effect to provide a new strategy to overcome bacterial resistance to AGAs.