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N. gonorrhoeae survives in association with monocytes. A. Survival of gonococci with human THP-1 monocytes at 2 and 5 hr post infection. Percent monocyte-associated gonococcal survival is calculated in reference to the number of viable gonococci cultured from infected THP1 cells after 1 hr of phagocytosis. Error bars are 6 standard deviation from the mean of 4 independent experiments. B: Viability of adherent and intracellular and extracellular GC-FA19 in differentiated THP-1 cells, i.e. adherent macrophages, were visualized with BacLight staining where red is dead and green is live gonococci. Adherent THP-1 cell membranes were permeabilized with 0.1% saponin to stain phagocytosed gonococci. i: 1 hr post infection stained without saponin. ii: 1 hr post infection stained in the presence of 0.1% saponin. iii: 5 hr post infection stained without saponin. iv: 5 hr post infection stained in the presence of 0.1% saponin. These data are representative of two independent experiments. C: Quantitative RTPCR of iron-responsive and-unresponsive genes in monocyte-associated GC-FA19 at 5 hrs post infection compared to 1 hr post infection. Error bars represent SD from the mean of three independent experiments. * P values (,0.005) were calculated in comparison to rmpM gene expression. N.S.: not significant. doi:10.1371/journal.pone.0087688.g001
Citations
... Studies to address this subject have been developed mainly in the biomedicine field using animal models. However, these studies show that microorganisms can indeed develop some mechanisms of resistance [74,75]. As shown in Figure 2, a possible mechanism is to secrete extracellular proteases, as done by Salmonella enterica to resist helical cationic AMPs [76]. ...
... As shown in Figure 2, a possible mechanism is to secrete extracellular proteases, as done by Salmonella enterica to resist helical cationic AMPs [76]. Other strategies are to release binding molecules as 'decoys' (such as negatively-charged membrane mimics, or hydrophilic bacterial polymers) [75]. Some microorganisms are even reducing their membrane anionic charge to decrease recognition by cationic AMPs, or using efflux pumps to drive them outside [77][78][79][80]. ...
... The first is the production of intracellular peptidases (as done by E. coli to cleave prolinerich AMPs) [81]. The change of intracellular targets is sometimes possible [75]. ...
Host-defense peptides (HDP) are emerging as promising phytosanitaries due to their potency, low plant, animal and environmental toxicity, and above all, low induction of antimicrobial resistance. These natural compounds, which have been used by animals and plants over millions of years to defend themselves against pathogens, are being discovered by genome mining, and then produced using biofactories. Moreover, truncated or otherwise modified peptides, including ultra-short ones, have been developed to improve their bioactivities and biodistribution, and also to reduce production costs. The synergistic combination of HDP and other antimicrobials, and the development of hybrid molecules have also given promising results. Finally, although their low induction of antimicrobial resistance is a big advantage, cautionary measures for the sustainable use of HDPs, such as the use of precision agriculture tools, were discussed.
... 141 AMP-loaded surfaces can effectively reduce biofilm, 142 but their fast release and low stability are shortcomings. 141,143 Other antibiotic-free bactericidal agents, as quaternary ammonium compounds, 127,144 polymers (e.g., chitosan and e-poly-l-lysine), 145,146 quorumsensing inhibitor, 147,148 chlorhexidine, 128,[149][150][151] and enzymes (e.g., deoxyribonuclease I and dispersin B), 152,153 are also promising in antimicrobial surface engineering. ...
Dental implants represent an illustrative example of successful medical devices used in increasing numbers to aid (partly) edentulous patients. Particularly in spite of the percutaneous nature of dental implant systems, their clinical success is remarkable. This clinical success is at least partly related to the effective surface treatment of the artificial dental root, providing appropriate physico-chemical properties to achieve osseointegration. The demographic changes in the world, however, with a rapidly increasing life-expectancy and an increase in patients suffering from co-morbidities that affect wound healing and bone metabolism, make that the performance of dental implants requires continuous improvement. An additional factor endangering the clinical success of dental implants is peri-implantitis, which affects both the soft and hard tissue interactions with dental implants. Here, we shed light on the optimization of dental implant surfaces via surface engineering. Depending on the region along the artificial dental root, different properties of the surface are required to optimize prevailing tissue response to facilitate osseointegration, improve soft tissue attachment, and exert antibacterial efficacy. As such, surface engineering represents an important tool for assuring the continued future success of dental implants.
... Due to the rapid and non-specific mechanisms of action, the risk of resistance development is generally thought to be low (Zasloff, 2002). Nonetheless, resistance to AMPs in bacteria does occur and several mechanisms of resistance have been described, including membrane and cell envelope structure alterations increasing positive charge, upregulation of efflux pumps, and proteolytic degradation of the peptides (Goytia et al., 2013;Ernst et al., 2015). For instance, resistance against the human cathelicidin LL-37 has been reported to involve degradation of the peptide by bacterial proteolytic enzymes, up-regulation of efflux pumps as well as bacterial-induced down-regulation of LL-37 expression in host cells (Bandurska et al., 2015). ...
... Under low calcium or magnesium ion concentrations, as in blood plasma, P. aeruginosa activates the pmr (polymyxin resistance) operon, which medicates the addition of N-arabinose to its lipopolysaccharide. This renders the outer surface of the bacterial cell more positively charged, repelling the cationic AMPs (Goytia et al., 2013). So, resistance of bacteria against AMPs is possible for several bacterial species, however development of such resistance against novel synthetic AMPs has not often been studied. ...
Over the past decades the use of medical devices, such as catheters, artificial heart valves, prosthetic joints, and other implants, has grown significantly. Despite continuous improvements in device design, surgical procedures, and wound care, biomaterial-associated infections (BAI) are still a major problem in modern medicine. Conventional antibiotic treatment often fails due to the low levels of antibiotic at the site of infection. The presence of biofilms on the biomaterial and/or the multidrug-resistant phenotype of the bacteria further impair the efficacy of antibiotic treatment. Removal of the biomaterial is then the last option to control the infection. Clearly, there is a pressing need for alternative strategies to prevent and treat BAI. Synthetic antimicrobial peptides (AMPs) are considered promising candidates as they are active against a broad spectrum of (antibiotic-resistant) planktonic bacteria and biofilms. Moreover, bacteria are less likely to develop resistance to these rapidly-acting peptides. In this review we highlight the four main strategies, three of which applying AMPs, in biomedical device manufacturing to prevent BAI. The first involves modification of the physicochemical characteristics of the surface of implants. Immobilization of AMPs on surfaces of medical devices with a variety of chemical techniques is essential in the second strategy. The main disadvantage of these two strategies relates to the limited antibacterial effect in the tissue surrounding the implant. This limitation is addressed by the third strategy that releases AMPs from a coating in a controlled fashion. Lastly, AMPs can be integrated in the design and manufacturing of additively manufactured/3D-printed implants, owing to the physicochemical characteristics of the implant material and the versatile manufacturing technologies compatible with antimicrobials incorporation. These novel technologies utilizing AMPs will contribute to development of novel and safe antimicrobial medical devices, reducing complications and associated costs of device infection.
... Any information on this aspect is available only from studies with animal model systems. Literature on what mechanisms bacteria develop to inactivate human cationic AMPs (CAMPs) has been reviewed [278]. One of the antidotes that bacteria employ to inactivate AMPs is to secrete extracellular proteases. ...
... Bacteria are able to target the PAMP-induced AMPs by disrupting the recognition mechanism. Other strategies of protection against AMPs include trapping the CAMPs through binding agents and hydrophilic bacterial polymers, export CAMPs by efflux pumps and altering intracellular targets [278]. The nature of resistance can be both adaptive and heritable [285]. ...
Crop losses due to pathogens are a major threat to global food security. Plants employ a multilayer defense against a pathogen including the use of physical barriers (cell wall), induction of hypersensitive defense response (HR), resistance (R) proteins, and synthesis of antimicrobial peptides (AMPs). Unlike a complex R gene-mediated immunity, AMPs directly target diverse microbial pathogens. Many a times, R-mediated immunity breaks down and plant defense is compromised. Although R-gene dependent pathogen resistance has been well studied, comparatively little is known about the interactions of AMPs with host defense and physiology. AMPs are ubiquitous, low molecular weight peptides that display broad spectrum resistance against bacteria, fungi and viruses. In plants, AMPs are mainly classified into cyclotides, defensins, thionins, lipid transfer proteins, snakins, and hevein-like vicilin-like and knottins. Genetic distance lineages suggest their conservation with minimal effect of speciation events during evolution. AMPs provide durable resistance in plants through a combination of membrane lysis and cellular toxicity of the pathogen. Plant hormones - gibberellins, ethylene, jasmonates, and salicylic acid, are among the physiological regulators that regulate the expression of AMPs. Transgenically produced AMP-plants have become a means showing that AMPs are able to mitigate host defense responses while providing durable resistance against pathogens.
Tissue engineering is one of the most important biotechnologies in the biomedical field. It requires the application of the principles of scientific engineering in order to design and build natural or synthetic biomaterials feasible for the maintenance of tissues and organs. Depending on the specific applications, the selection of the proper material remains a significant clinical concern. Implant-associated infection is one of the most severe complications in orthopedic implant surgeries. The treatment of these infections is difficult because the surface of the implant serves not only as a substrate for the formation of the biofilm, but also for the selection of multidrug-resistant bacterial strains. Therefore, a promising new approach for prevention of implant-related infection involves development of new implantable, non-antibiotic-based biomaterials. This review provides a brief overview of antimicrobial peptide-based biomaterials—especially those coated with lactoferrin.
During infection, the sexually transmitted pathogen
Neisseria gonorrhoeae
(the gonococcus) encounters numerous host-derived antimicrobials including cationic antimicrobial peptides (CAMPs) produced by epithelial and phagocytic cells. CAMPs have both direct and indirect killing mechanisms and help link the innate and adaptive immune responses during infection. Gonococcal CAMP resistance is likely important for avoidance of host nonoxidative killing systems expressed by polymorphonuclear granulocytes (e.g., neutrophils) and intracellular survival. Previously studied gonococcal CAMP resistance mechanisms include modification of lipid A with phosphoethanolamine by LptA and export of CAMPs by the MtrCDE efflux pump. In the related pathogen,
Neisseria meningitidis,
a two-component regulatory system (2CRS) termed MisR-MisS has been shown to contribute to the capacity of the meningococcus to resist CAMP killing. We report that the gonococcal MisR response regulator, but not the MisS sensor kinase, is involved in constitutive and inducible CAMP resistance and is also required for intrinsic low-level resistance to aminoglycosides. The 4- to 8-fold increased susceptibility of
misR
-deficient gonococci to CAMPs and aminoglycosides was independent of phosphoethanolamine decoration of lipid A and levels of the MtrCDE efflux pump, and seemed to correlate with a general increase in membrane permeability. Transcriptional profiling and biochemical studies confirmed that expression of
lptA
and
mtrCDE
was not impacted by loss of MisR. However, several genes encoding proteins involved in membrane integrity and redox control gave evidence of being MisR-regulated. We propose that MisR modulates levels of gonococcal susceptibility to antimicrobials by influencing expression of genes involved in determining membrane integrity.
Currently, antimicrobial drug resistance is a global problem that threatens to precipitate a ‘Post-antibiotic era’ in which the ability of common infections and minor injuries to kill is a very real possibility. A potential solution to this problem is the development of host defence peptides, which are endogenous antibiotics that kill microbes via membranolytic action, based in part on the belief that microbes were unlikely to develop resistance to this action. However, the incidence of microbes exhibiting resistance to the action of host defence peptides is growing and an increasingly diverse spectrum of mechanisms is being reported to underpin this resistance. These mechanisms can be broadly categorized as those that either: destroy these peptides, such as through the production of bacterial proteases; intercept/shield these peptides, such as by the release of host cell proteoglycans by bacterial enzymes; or export these peptides, such as via the use of bacterial efflux pumps. Here we give an overview of these mechanisms, with a focus on recent developments in this area, and then discuss the potential of inhibitors of these resistance mechanisms to treat infections due to bacterial pathogens.
Antimicrobial peptides (AMPs) are at the front-line of host defense during infection and play critical roles both in reducing the microbial load early during infection and in linking innate to adaptive immunity. However, successful pathogens have developed mechanisms to resist AMPs. Although considerable progress has been made in elucidating AMP-resistance mechanisms of pathogenic bacteria in vitro, less is known regarding the in vivo significance of such resistance. Nevertheless, progress has been made in this area, largely by using murine models and, in two instances, human models of infection. Herein, we review progress on the use of in vivo infection models in AMP research and discuss the AMP resistance mechanisms that have been established by in vivo studies to contribute to microbial infection. We posit that in vivo infection models are essential tools for investigators to understand the significance to pathogenesis of genetic changes that impact levels of bacterial susceptibility to AMPs. This article is part of a Special Issue entitled: Bacterial Resistance to Antimicrobial Peptides.
Copyright © 2015. Published by Elsevier B.V.
Phosphoethanolamine (PEA) decoration of lipid A produced by Neisseria gonorrhoeae has been linked to bacterial resistance to cationic antimicrobial peptides/proteins (CAMPs) and in vivo fitness during experimental infection. We now report that the lptA gene, which encodes the PEA transferase responsible for this decoration, is in an operon and that high-frequency mutation
in a polynucleotide repeat within lptA can influence gonococcal resistance to CAMPs.
