The Strategies of Pathogen-Oriented Therapy on Circumventing Antimicrobial Resistance

Abstract

The emerging antimicrobial resistance (AMR) poses serious threats to the global public health. Conventional antibiotics have been eclipsed in combating with drug-resistant bacteria. Moreover, the developing and deploying of novel antimicrobial drugs have trudged, as few new antibiotics are being developed over time and even fewer of them can hit the market. Alternative therapeutic strategies to resolve the AMR crisis are urgently required. Pathogen-oriented therapy (POT) springs up as a promising approach in circumventing antibiotic resistance. The tactic underling POT is applying antibacterial compounds or materials directly to infected regions to treat specific bacteria species or strains with goals of improving the drug efficacy and reducing nontargeting and the development of drug resistance. This review exemplifies recent trends in the development of POTs for circumventing AMR, including the adoption of antibiotic-antibiotic conjugates, antimicrobial peptides, therapeutic monoclonal antibodies, nanotechnologies, CRISPR-Cas systems, and microbiota modulations. Employing these alternative approaches alone or in combination shows promising advantages for addressing the growing clinical embarrassment of antibiotics in fighting drug-resistant bacteria.

Figure 1

The structure of teixobactin and its performance against pathogenic microorganisms. (a) Schematic structure of teixobactin. (b) Activity of teixobactin against pathogenic microorganisms. (c) Time-dependent killing of pathogens by teixobactin. S. aureus grew to early (upper left) and late (upper right) exponential phase and challenged with antibiotics. Teixobactin treatment resulted in lysis (lower left) and resistance acquisition during serial passaging in the presence of sub-MIC levels of antimicrobials (bottom lower right). The y-axis is the highest concentration the cells grew during passaging [126]. Copyright © 2020, Springer Nature.

Figure 2

Darobactin produced by a silent operon of P. khanii is a bactericidal antibiotic. (a) Darobactin structure. (b) Time-dependent killing of E. coli MG1655 by darobactin. An exponential culture of E. coli MG1655 was challenged with 16x MIC antibiotics. (c) Schematic of the Bam complex. IM: inner membrane; OM: outer membrane. (d) Scanning electron microscopy analysis of E. coli MG1655 treated with 16x MIC darobactin. Scale bars, 1 μm [127]. Copyright © 2020, Springer Nature.

Figure 3

The structures of the chimeric polymyxin B1 and their mechanism studies using fluorescence and transmission electron microscopy. (a) The structures of chimeric polymyxin B1. (b) Fluorescence microscopy of E. coli ATCC 25922 cells grown in MH-II and stained with FM4-64, DAPI, or SYTOX-green, without treatment. (c) Transmission electron microscopy of E. coli ATCC 25922 untreated or grown with 3 or 4 at concentrations causing about 50% growth inhibition (about 0.1 mg L⁻¹) (n = 3 biologically independent experiments). Scale bars, 200 nm [128]. Copyright © 2020, Springer Nature.

Figure 4

The model of novel of antibody-antibiotic and its antibacterial properties. (a) Model of AAC. (b) Intracellular USA300 were added to a monolayer of MG63 with antibody, AAC, or a mixture of antibody plus rifampicin in media containing vancomycin (vanco). Surviving bacteria were enumerated 24 h later. (c) AAC kills intracellular reservoirs of MRSA in vivo. (d) 10 mice per group were injected with human IgG to achieve a concentration of 10 mg/mL, then infected with MRSA. Treatment as indicated was begun 24 h after infection [155]. Copyright © 2015, Springer Nature.

Figure 5

The schematic structure and antibacterial efficacy of targeted antibiotic-loaded nanoparticles. (a) A schematic illustration of the therapeutic nanoparticle system consisting of pSiNP, chemotherapeutic agent, and homing peptide. (b) The CARG peptide shows selective binding to cultured S. aureus in vitro and homes to infected lungs in vivo. (c) The CARG does not recognize cultured Pseudomonas aeruginosa bacteria or lung tissue infected with these bacteria. (d) Biodistribution of nanoparticles obtained from the luminescence intensity in each organ. (e) Survival rate (n = 9) of mice after intratracheal inoculation with 5 × 10⁷ colony-forming units (CFU) of S. aureus [224]. Copyright © 2018, Springer Nature.

Figure 6

RGN constructs delivered by bacteriophage particles (ΦRGN) exhibit efficient and specific antimicrobial effects against strains harboring plasmid or chromosomal target sequences. (a) Bacteriophage-delivered RGN constructs differentially affect host cell physiology in a sequence-dependent manner. (b) Treatment of EMG2 wild-type (WT) or EMG2 containing native resistance plasmids, pNDM-1 (encoding bla_NDM-1), or pSHV-18 (encoding bla_SHV-18), with SM buffer, ΦRGN_ndm-1, ΦRGN_shv-18, or multiplexed ΦRGN_ndm-1/shv-18 at a multiplicity of infection (MOI) ~20 showed sequence-dependent cytotoxicity as evidenced by a strain-specific reduction in viable cell counts (n = 3). CFU: colony-forming units. (c) E. coli EMG2 WT or EMG2 gyrA_D87G populations were treated with SM buffer, ΦRGN_ndm-1, or ΦRGNgyrA_D87G at MOI ~20, and viable cells were determined by plating onto Luria-Bertani agar (n = 3) [231]. Copyright © 2014, Springer Nature.

Figure 7

The structures of antibacterial drones (ABD) and their activities in vitro and in vivo. (a) Genetic maps of SaPI2 and its ABD derivatives. (b) ABD constructs. ABD2001 was derived from the prototypical SaPI2 by deleting toxin genes tst and eta and the capsid morphogenesis genes cpmA and cpmB. ABD2002–2006 were derived from ABD2001 by the insertion of the listed genes. (c) Killing of S. aureus by ABD2003 and of L. monocytogenes by ABD2004. Suitable dilutions of ABD2002, ABD2003, or ABD2004 particle preparations were mixed with RN1, RN1∆agr, or L. monocytogenes SK1442, plated on Tc5, and incubated at 37°C for 48 h. (d) Blockade of SC murine infections by ABDs [234]. Copyright © 2018, Springer Nature.

Figure 8

Cas12a-mediated release of small molecules and enzymes from PEG hydrogels. (a) ssDNA acts as a cleavable linker for attaching payloads to an inert PEG matrix. hν: light energy. (b) Activation of Cas12a and fluorophore release (t = 8 hours) is defined by the complementarity between a dsDNA sequence and the gRNA of Cas12a. (c) Functional enzymes can be anchored into the hydrogel and released by Cas12a in sufficient quantities for visual detection in an HRP activity assay within minutes. A.U.: arbitrary units. (d) Release of a tethered fluorophore by Cas12a is initiated only upon the introduction of a specific dsDNA trigger and not a scrambled dsDNA control sequence [244]. Copyright © 2019, The American Association for the Advancement of Science.

Figure 9

Schematic diagram of constructing a functional probiotic strain and its activity against P. aeruginosa infection. (a) Vector-host system created in the E. coli Nissle strain by auxotrophic complementation to stabilize plasmid retention. (b) P. aeruginosa was cocultured with engineered EcN for 20 h to evaluate its effect on biofilm formation. (c) The survival rate of each treatment group was quantified until all the nematodes in the infection group had died (96 h). (d) Evaluation of the engineered probiotic strain in a mouse infection model. (e) Prophylactic activity of engineered EcN against P. aeruginosa infection [264]. Copyright © 2017, Springer Nature.