Potential risks of treating bacterial infections with a combination of β-lactam and aminoglycoside antibiotics: A systematic quantification of antibiotic interactions in E. coli blood stream infection isolates

Research Progress on the Combination of Quorum-Sensing Inhibitors and Antibiotics against Bacterial Resistance

Bacterial virulence factors and biofilm development can be controlled by the quorum-sensing (QS) system, which is also intimately linked to antibiotic resistance in bacteria. In previous studies, many researchers found that quorum-sensing inhibitors (QSIs) can affect the development of bacterial biofilms and prevent the synthesis of many virulence factors. However, QSIs alone have a limited ability to suppress bacteria. Fortunately, when QSIs are combined with antibiotics, they have a better therapeutic effect, and it has even been demonstrated that the two together have a synergistic antibacterial effect, which not only ensures bactericidal efficiency but also avoids the resistance caused by excessive use of antibiotics. In addition, some progress has been made through in vivo studies on the combination of QSIs and antibiotics. This article mainly expounds on the specific effect of QSIs combined with antibiotics on bacteria and the combined antibacterial mechanism of some QSIs and antibiotics. These studies will provide new strategies and means for the clinical treatment of bacterial infections in the future.

Within-species variability of antibiotic interactions in Gram-negative bacteria

Treatments with antibiotic combinations are becoming increasingly important even though the supposed clinical benefits of combinations are, in many cases, unclear. Here, we systematically examined how several clinically used antibiotics interact and affect the antimicrobial efficacy against five especially problematic Gram-negative pathogens. A total of 232 bacterial isolates were tested against different pairwise antibiotic combinations spanning five classes, and the ability of all combinations in inhibiting growth was quantified. Descriptive statistics, principal component analysis (PCA), and Spearman's rank correlation matrix were used to determine the correlations between the different combinations on interaction outcome. Several important conclusions can be drawn from the 696 examined interactions. Firstly, within a species, the interactions are in general conserved but can be isolate-specific for a given antibiotic combination and can range from antagonistic to synergistic. Secondly, additive and antagonistic interactions are the most common observed across species and antibiotics, with 87.1% of isolate-antibiotic combinations being additive, 11.6% antagonistic, and only 0.3% showing synergy. These findings suggest that to achieve the highest precision and efficacy of combination therapy, not only isolate-specific interaction profiling ought to be routinely performed, in particular to avoid using drug combinations that show antagonistic interaction and an expected associated reduction in efficacy, but also discovering rare and potentially valuable synergistic interactions.IMPORTANCEAntibiotic combinations are often used to treat bacterial infections, which aim to increase treatment efficacy and reduce resistance evolution. Typically, it is assumed that one specific antibiotic combination has the same effect on different isolates of the same species, i.e., the interaction is conserved. Here, we tested this idea by examining how several clinically used antibiotics interact and affect the antimicrobial efficacy against several bacterial pathogens. Our results show that, even though within a species the interactions are often conserved, there are also isolate-specific differences for a given antibiotic combination that can range from antagonistic to synergistic. These findings suggest that isolate-specific interaction profiling ought to be performed in clinical microbiology routine to avoid using antagonistic drug combinations that might reduce treatment efficacy.

Development of cannabidiol derivatives as potent broad-spectrum antibacterial agents with membrane-disruptive mechanism

The emergence of antibiotic resistance has brought a significant burden to public health. Here, we designed and synthesized a series of cannabidiol derivatives by biomimicking the structure and function of cationic antibacterial peptides. This is the first report on the design of cannabidiol derivatives as broad-spectrum antibacterial agents. Through the structure-activity relationship (SAR) study, we found a lead compound 23 that killed both Gram-negative and Gram-positive bacteria via a membrane-targeting mechanism of action with low resistance frequencies. Compound 23 also exhibited very weak hemolytic activity, low toxicity toward mammalian cells, and rapid bactericidal properties. To further validate the membrane action mechanism of compound 23, we performed transcriptomic analysis using RNA-seq, which revealed that treatment with compound 23 altered many cell wall/membrane/envelope biogenesis-related genes in Gram-positive and Gram-negative bacteria. More importantly, compound 23 showed potent in vivo antibacterial efficacy in murine corneal infection models caused by Staphylococcus aureus or Pseudomonas aeruginosa. These findings would provide a new design idea for the discovery of novel broad-spectrum antibacterial agents to overcome the antibiotic resistance crisis.

Evaluation of the Antibacterial Effect of Aurone-Derived Triazoles on Staphylococcus aureus

Infections caused by antibiotic-resistant bacteria continue to pose a significant public health threat despite their overall decreasing numbers in the last two decades. One group of compounds fundamental to the search for new agents is low-cost natural products. In this study, we explored a group of newly synthesized novel aurone-derived triazole compounds to identify those with pharmaceutical potential as inhibitors of antibiotic-resistant Staphylococcus aureus. Using the broth microdilution method, antibacterial activities against methicillin-resistant S. aureus ATCC 43300 (MRSA) and methicillin-sensitive S. aureus ATCC 29213 (MSSA) were identified for four aurone-derived triazole compounds, AT106, AT116, AT125, and AT137, using the half-maximal inhibitory concentrations for the bacteria (IC50) and mammalian cell lines (CC50). Compounds AT125 and AT137 were identified to have pharmaceutical potential as the IC50 values against MRSA were 5.412 µM and 3.870 µM, whereas the CC50 values measured on HepG2 cells were 50.57 µM and 39.81 µM, respectively, resulting in selectivity indexes (SI) > 10. Compounds AT106 and AT116 were also selected for further study. IC50 values for these compounds were 5.439 µM and 3.178 µM, and the CC50 values were 60.33 µM and 50.87 µM, respectively; however, SI values > 10 were for MSSA only. Furthermore, none of the selected compounds showed significant hemolytic activity for human erythrocytes. We also tested the four compounds against S. aureus biofilms. Although AT116 and AT125 successfully disrupted MSSA biofilms, there was no measurable potency against MRSA biofilms. Checkerboard antibiotic assays to identify inhibitory mechanisms for these compounds indicated activity against bacterial cell membranes and cell walls, supporting the pharmaceutical potential for aurone-derived triazoles against antibiotic-resistant bacteria. Examining structure-activity relationships between the four compounds in this study and other aurone-derived triazoles in our library suggest that substitution with a halogen on either the salicyl ring or triazole aryl group along with triazoles having nitrile groups improves anti-Staphylococcal activity with the location of the functionality being very important.

Uncovering the Important Genetic Factors for Growth during Cefotaxime-Gentamicin Combination Treatment in blaCTX-M-1 Encoding Escherichia coli

Due to the rapid spread of CTX-M type ESBLs, the rate of resistance to third-generation cephalosporin has increased among Gram-negative bacteria, especially in Escherichia coli, and there is a need to find ways to re-sensitize ESBL E. coli to cephalosporin treatment. A previous study showed that genes involved in protein synthesis were significantly up-regulated in the presence of subinhibitory concentration of cefotaxime (CTX) in a CTX-M-1-producing E. coli. In this study, the interaction between CTX and gentamicin (GEN), targeting protein synthesis, was evaluated in MG1655/pTF2, and the MIC of CTX was strongly reduced (128-fold) in the presence of this combnation therapy. Since the underlying mechanism behind this synergy is not known, we constructed a saturated transposon mutant library in MG1655/pTF2::bla_CTX-M-1 containing 315,925 unique transposon insertions to measure mutant depletion upon exposure to CTX, GEN, and combination treatment of CTX and GEN by Transposon Directed Insertion-site Sequencing (TraDIS). We identified 57 genes that were depleted (log₂FC ≤ -2 and with q.value ≤ 0.01) during exposure to CTX, 18 for GEN, and 31 for combination treatment of CTX and GEN. For validation, we deleted eight genes that were either uniquely identified in combination treatment, overlapped with monotherapy of GEN, or were shared between combination treatment and monotherapy with CTX and GEN. Of these genes, we found that the inactivation of dnaK, mnmA, rsgA, and ybeD increased the efficacy of both CTX and GEN treatment, the inactivation of cpxR and yafN increased the efficacy of only CTX, and the inactivation of mnmA, rsgA, and ybeD resulted in increased synergy between CTX and GEN. Thus, the study points to putative targets for helper drugs that can restore susceptibility to these important drugs, and it indicates that genes involved in protein synthesis are essential for the synergy between these two drugs. In summary, the study identified mutants that sensitize ESBL-producing E. coli to CTX and a combination of CTX and GEN, and it increased our understanding of the mechanism behind synergy between β-lactam and aminoglycoside drugs. This forms a framework for developing new strategies to combat infections caused by resistant bacteria.

R R, L. F L, M.C.G DR, N.B C, S.C D, O. L F. Advances and perspectives for antimicrobial peptide and combinatory therapies

Antimicrobial peptides (AMPs) have shown cell membrane-directed mechanisms of action. This specificity can be effective against infectious agents that have acquired resistance to conventional drugs. The AMPs' membrane-specificity and their great potential to combat resistant microbes has brought hope to the medical/therapeutic scene. The high death rate worldwide due to antimicrobial resistance (AMR) has pushed forward the search for new molecules and product developments, mainly antibiotics. In the current scenario, other strategies including the association of two or more drugs have contributed to the treatment of difficult-to-treat infectious diseases, above all, those caused by bacteria. In this context, the synergistic action of AMPs associated with current antibiotic therapy can bring important results for the production of new and effective drugs to overcome AMR. This review presents the advances obtained in the last 5 years in medical/antibiotic therapy, with the use of products based on AMPs, as well as perspectives on the potentialized effects of current drugs combined with AMPs for the treatment of bacterial infectious diseases.