scholarly journals De NovoGuanine Biosynthesis but Not the Riboswitch-Regulated Purine Salvage Pathway Is Required for Staphylococcus aureus InfectionIn Vivo

2016 ◽  
Vol 198 (14) ◽  
pp. 2001-2015 ◽  
Author(s):  
Eric M. Kofoed ◽  
Donghong Yan ◽  
Anand K. Katakam ◽  
Mike Reichelt ◽  
Baiwei Lin ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
De Novo ◽  
Alternative Promoter ◽  
Antibacterial Drug ◽  
Salvage Pathway ◽  
Promoter Elements ◽  
Purine Salvage ◽  
Content Type ◽  
Therapeutic Utility

ABSTRACTDe novoguanine biosynthesis is an evolutionarily conserved pathway that creates sufficient nucleotides to support DNA replication, transcription, and translation. Bacteria can also salvage nutrients from the environment to supplement thede novopathway, but the relative importance of either pathway duringStaphylococcus aureusinfection is not known. InS. aureus, genes important for bothde novoand salvage pathways are regulated by a guanine riboswitch. Bacterial riboswitches have attracted attention as a novel class of antibacterial drug targets because they have high affinity for small molecules, are absent in humans, and regulate the expression of multiple genes, including those essential for cell viability. Genetic and biophysical methods confirm the existence of a bona fide guanine riboswitch upstream of an operon encoding xanthine phosphoribosyltransferase (xpt), xanthine permease (pbuX), inosine-5′-monophosphate dehydrogenase (guaB), and GMP synthetase (guaA) that represses the expression of these genes in response to guanine. We found thatS. aureusguaBandguaAare also transcribed independently of riboswitch control by alternative promoter elements. Deletion ofxpt-pbuX-guaB-guaAgenes resulted in guanine auxotrophy, failure to grow in human serum, profound abnormalities in cell morphology, and avirulence in mouse infection models, whereas deletion of the purine salvage genesxpt-pbuXhad none of these effects. Disruption ofguaBorguaArecapitulates thexpt-pbuX-guaB-guaAdeletionin vivo. In total, the data demonstrate that targeting the guanine riboswitch alone is insufficient to treatS. aureusinfections but that inhibition ofguaAorguaBcould have therapeutic utility.IMPORTANCEDe novoguanine biosynthesis and purine salvage genes were reported to be regulated by a guanine riboswitch inStaphylococcus aureus. We demonstrate here that this is not true, because alternative promoter elements that uncouple thede novopathway from riboswitch regulation were identified. We found that in animal models of infection, the purine salvage pathway is insufficient forS. aureussurvival in the absence ofde novoguanine biosynthesis. These data suggest targeting thede novoguanine biosynthesis pathway may have therapeutic utility in the treatment ofS. aureusinfections.

scholarly journals A Mutation in the PP2C Phosphatase Gene in a Staphylococcus aureus USA300 Clinical Isolate with Reduced Susceptibility to Vancomycin and Daptomycin

2012 ◽  
Vol 56 (10) ◽  
pp. 5212-5223 ◽  
Author(s):  
Karla D. Passalacqua ◽  
Sarah W. Satola ◽  
Emily K. Crispell ◽  
Timothy D. Read
Keyword(s):  
Staphylococcus Aureus ◽  
Metal Binding ◽  
De Novo ◽  
Surface Protein ◽  
Complex Nature ◽  
Insertion Mutation ◽  
Content Type ◽  
Metal Binding Domain ◽  
Multiple Routes

ABSTRACTMethicillin-resistantStaphylococcus aureus(MRSA) strains with reduced susceptibility to vancomycin (MIC of 4 to 8 μg/ml) are referred to as vancomycin-intermediateS. aureus(VISA). In this study, we characterized two isogenic USA300S. aureusisolates collected sequentially from a single patient with endocarditis where theS. aureusisolate changed from being susceptible to vancomycin (VSSA) (1 μg/ml) to VISA (8 μg/ml). In addition, the VISA isolate lost beta-lactamase activity and showed increased resistance to daptomycin and linezolid. The two strains did not differ in growth rate, but the VISA isolate had a thickened cell wall and was less autolytic. Transcriptome sequencing (RNA-seq) analysis comparing the two isolates grown to late exponential phase showed significant differences in transcription of cell surface protein genes (spa, SBI [second immunoglobulin-binding protein ofS. aureus], and fibrinogen-binding proteins), regulatory genes (agrBCA, RNAIII,sarT, andsaeRS), and others. Using whole-genome shotgun resequencing, we identified 6 insertion/deletion mutations between the VSSA and VISA isolates. A protein phosphatase 2C (PP2C) family phosphatase had a 6-bp (nonframeshift) insertion mutation in a highly conserved metal binding domain. Complementation of the clinical VISA isolate with a wild-type copy of the PP2C gene reduced the vancomycin and daptomycin MICs and increased autolytic activity, suggesting that this gene contributed to the reduced vancomycin susceptibility phenotype acquiredin vivo. Creation ofde novomutants from the VSSA strain resulted in different mutations, demonstrating that reduced susceptibility to vancomycin in USA300 strains can occur via multiple routes, highlighting the complex nature of the VISA phenotype.

scholarly journals Borrelia burgdorferi Harbors a Transport System Essential for Purine Salvage and Mammalian Infection

2012 ◽  
Vol 80 (9) ◽  
pp. 3086-3093 ◽  
Author(s):  
Sunny Jain ◽  
Selina Sutchu ◽  
Patricia A. Rosa ◽  
Rebecca Byram ◽  
Mollie W. Jewett
Keyword(s):  
Lyme Disease ◽  
Borrelia Burgdorferi ◽  
Transport System ◽  
De Novo ◽  
Transport Systems ◽  
Mammalian Host ◽  
Salvage Pathway ◽  
Purine Salvage ◽  
Content Type ◽  
Obligate Pathogen

ABSTRACTBorrelia burgdorferiis the tick-borne bacterium that causes the multistage inflammatory disease Lyme disease.B. burgdorferihas a reduced genome and lacks the enzymes required forde novosynthesis of purines for synthesis of RNA and DNA. Therefore, this obligate pathogen is dependent upon the tick vector and mammalian host environments for salvage of purine bases for nucleic acid biosynthesis. This pathway is vital forB. burgdorferisurvival throughout its infectious cycle, as key enzymes in the purine salvage pathway are essential for the ability of the spirochete to infect mice and critical for spirochete replication in the tick. The transport of preformed purines into the spirochete is the first step in the purine salvage pathway and may represent a novel therapeutic target and/or means to deliver antispirochete molecules to the pathogen. However, the transport systems critical for purine salvage byB. burgdorferihave yet to be identified. Herein, we demonstrate that the genesbbb22andbbb23, present onB. burgdorferi's essential plasmid circular plasmid 26 (cp26), encode key purine transport proteins. BBB22 and/or BBB23 is essential for hypoxanthine transport and contributes to the transport of adenine and guanine. Furthermore,B. burgdorferilackingbbb22-23was noninfectious in mice up to a dose of 1 × 107spirochetes. Together, our data establish thatbbb22-23encode purine permeases critical forB. burgdorferimammalian infectivity, suggesting that this transport system may serve as a novel antimicrobial target for the treatment of Lyme disease.

Paics, a De Novo Purine Synthetic Enzyme, Is a Novel Target for AML Therapy

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 1390-1390
Author(s):  
Takuji Yamauchi ◽  
Kohta Miyawaki ◽  
Yuichiro Semba ◽  
Fumihiko Nakao ◽  
Takeshi Sugio ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Enzymatic Activity ◽  
Cell Survival ◽  
Cell Lines ◽  
De Novo ◽  
Salvage Pathway ◽  
Purine Salvage ◽  
Genome Wide ◽  
Pdx Models

Progress has been made in deciphering molecular mechanisms underlying AML pathogenesis due in part to near-complete understanding of AML genomes. However, AML is yet a devastating disease with a long-term survival rate of less than 30%, underscoring an urgent need for the development of additional therapeutic modalities. To identify novel targets for AML therapy, we performed genome-wide CRISPR-Cas9 dropout screens employing two mouse AML cell lines (CALM/AF10 and MLL/AF9), followed by a second screen in vivo. These two cell lines, which we established, harbor wild-type (WT) Trp53with normal karyotype, enabling us to interpret screening results more easily due to a "clean" genetic background. We then validated our findings using human AML cell lines and patient-derived xenograft (PDX) models (Yamauchi et al. Cancer Cell 2018). In the current study, we assessed the screening results furtherusing MAGeCK MLE program (Li et al. Genome Biology 2015)and the DepMap (https://depmap.org/), a publicly available genome-wide CRISPR-Cas9 screen datasets of cancer cell lines including 15 human AML cell lines. We show that PAICS (Phosphoribosylaminoimidazole carboxylase), which encodes an enzyme involved in de novo purine biosynthesis, is a molecule essential for AML cell survival. MRT252040, a newly-developed PAICS inhibitor (PAICSi), efficiently killed AML cell lines with different genetic backgrounds and significantly prolonged survival of AML PDX models. Furthermore, we investigated the mechanism action of PAICSi employing additional functional screens: CRISPR-Cas9 mutagenesis scan of all Paicscoding exons and a genome-wide CRISPR/Cas9 dropout screen in the presence of PAICSi. Read counts for each Paics-targeted single-guide RNA (sgRNA) significantly decreased in vitro (AML cell lines) and in vivo (mouse AML model). We then assessed the functional significance of PAICS inhibition in AML cell survival via shRNA-mediated PAICSknockdown. AML cells expressing PAICS shRNA exhibited a proliferative disadvantage compared to non-transduced cells or those expressing scrambled shRNA, indicating a toxic effect of PAICS depletion in AML cells. We next asked whether inhibition of PAICS enzymatic activity affects AML cell proliferation and/or apoptosis using PAICSi. We assessed AML growth rate, cell cycle status and apoptosis and found that inhibition of PAICS enzymatic activity delays AML cell proliferation via inducing cell cycle arrest and apoptosis. As expected, CRISPR-Cas9 mutagenesis scan showed that sgRNAs targeting the exonic regions relevant to PAICS enzymatic activity were significantly decreased after the 16-day incubation. We next performed genome-wide CRISPR-Cas9 screens in the presence of PAICSi, followed by second screens using a small-scale sgRNA library containing 8-10 sgRNAs per candidate gene.We identified genes potentially involved in PAICSi resistance as well as those whose loss are synthetic lethal to PAICS inhibition. X-box-binding protein 1 (Xbp1) was among the top hits in the genes relevant to PAICSi resistance genes, and sgRNAs targeting Xbp1significantly enriched in the presence of PAICSi. In contrast, sgRNAs targeting Slc43a3or Hprt, both of which are implicated in the purine salvage pathway, were significantly dropped-out, indicating that PAICSi-mediated anti-leukemia effects can be enhanced upon concurrentinhibition of the purine salvage pathway. Finally, we explored potential anti-leukemia effects of PAICSi in vivo using AML PDX models established from two human AML lines. PAICSi exhibited anti-leukemic activity, as evidenced by the lower leukemia burden in peripheral blood and bone marrow of PAICSi-treated mice. They survived significantly longer than vehicle-treated mice, indicative of therapeutic efficacy of PAICSimonotherapy against AML in vivo. In summary, we identified PAICS as an essential gene for AML cell survival. We propose that pharmacological targeting of the de-novo purine synthesis pathway via PAICSi is a potential therapeutic strategy for AML therapy. Disclosures Akashi: Celgene, Kyowa Kirin, Astellas, Shionogi, Asahi Kasei, Chugai, Bristol-Myers Squibb: Research Funding; Sumitomo Dainippon, Kyowa Kirin: Consultancy.

scholarly journals Exogenous Alginate Protects Staphylococcus aureus from Killing by Pseudomonas aeruginosa

2019 ◽  
Vol 202 (8) ◽  
Author(s):  
Courtney E. Price ◽  
Dustin G. Brown ◽  
Dominique H. Limoli ◽  
Vanessa V. Phelan ◽  
George A. O’Toole
Keyword(s):  
Staphylococcus Aureus ◽  
Pseudomonas Aeruginosa ◽  
Physical Space ◽  
Late Time ◽  
Protective Effects ◽  
Content Type ◽  
Alginate Production ◽  
The Impact

ABSTRACT Cystic fibrosis (CF) patients chronically infected with both Pseudomonas aeruginosa and Staphylococcus aureus have worse health outcomes than patients who are monoinfected with either P. aeruginosa or S. aureus. We showed previously that mucoid strains of P. aeruginosa can coexist with S. aureus in vitro due to the transcriptional downregulation of several toxic exoproducts typically produced by P. aeruginosa, including siderophores, rhamnolipids, and HQNO (2-heptyl-4-hydroxyquinoline N-oxide). Here, we demonstrate that exogenous alginate protects S. aureus from P. aeruginosa in both planktonic and biofilm coculture models under a variety of nutritional conditions. S. aureus protection in the presence of exogenous alginate is due to the transcriptional downregulation of pvdA, a gene required for the production of the iron-scavenging siderophore pyoverdine as well as the downregulation of the PQS (Pseudomonas quinolone signal) (2-heptyl-3,4-dihydroxyquinoline) quorum sensing system. The impact of exogenous alginate is independent of endogenous alginate production. We further demonstrate that coculture of mucoid P. aeruginosa with nonmucoid P. aeruginosa strains can mitigate the killing of S. aureus by the nonmucoid strain of P. aeruginosa, indicating that the mechanism that we describe here may function in vivo in the context of mixed infections. Finally, we investigated a panel of mucoid clinical isolates that retain the ability to kill S. aureus at late time points and show that each strain has a unique expression profile, indicating that mucoid isolates can overcome the S. aureus-protective effects of mucoidy in a strain-specific manner. IMPORTANCE CF patients are chronically infected by polymicrobial communities. The two dominant bacterial pathogens that infect the lungs of CF patients are P. aeruginosa and S. aureus, with ∼30% of patients coinfected by both species. Such coinfected individuals have worse outcomes than monoinfected patients, and both species persist within the same physical space. A variety of host and environmental factors have been demonstrated to promote P. aeruginosa-S. aureus coexistence, despite evidence that P. aeruginosa kills S. aureus when these organisms are cocultured in vitro. Thus, a better understanding of P. aeruginosa-S. aureus interactions, particularly mechanisms by which these microorganisms are able to coexist in proximal physical space, will lead to better-informed treatments for chronic polymicrobial infections.

scholarly journals Effects of Tedizolid Phosphate on Survival Outcomes and Suppression of Production of Staphylococcal Toxins in a Rabbit Model of Methicillin-Resistant Staphylococcus aureus Necrotizing Pneumonia

2017 ◽  
Vol 61 (4) ◽  
Author(s):  
Vien T. M. Le ◽  
Hoan N. Le ◽  
Marcos Gabriel Pinheiro ◽  
Kenneth J. Hahn ◽  
Mary L. Dinh ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Bacterial Production ◽  
Protective Efficacy ◽  
Survival Rates ◽  
Rabbit Model ◽  
Rank Test ◽  
Necrotizing Pneumonia ◽  
Time Curve ◽  
Content Type

ABSTRACT The protective efficacy of tedizolid phosphate, a novel oxazolidinone that potently inhibits bacterial protein synthesis, was compared to those of linezolid, vancomycin, and saline in a rabbit model of Staphylococcus aureus necrotizing pneumonia. Tedizolid phosphate was administered to rabbits at 6 mg/kg of body weight intravenously twice daily, which yielded values of the 24-h area under the concentration-time curve approximating those found in humans. The overall survival rate was 83% for rabbits treated with 6 mg/kg tedizolid phosphate twice daily and 83% for those treated with 50 mg/kg linezolid thrice daily (P = 0.66 by the log-rank test versus the results obtained with tedizolid phosphate). These survival rates were significantly greater than the survival rates of 17% for rabbits treated with 30 mg/kg vancomycin twice daily (P = 0.003) and 17% for rabbits treated with saline (P = 0.002). The bacterial count in the lungs of rabbits treated with tedizolid phosphate was significantly decreased compared to that in the lungs of rabbits treated with saline, although it was not significantly different from that in the lungs of rabbits treated with vancomycin or linezolid. The in vivo bacterial production of alpha-toxin and Panton-Valentine leukocidin, two key S. aureus-secreted toxins that play critical roles in the pathogenesis of necrotizing pneumonia, in the lungs of rabbits treated with tedizolid phosphate and linezolid was significantly inhibited compared to that in the lungs of rabbits treated with vancomycin or saline. Taken together, these results indicate that tedizolid phosphate is superior to vancomycin for the treatment of S. aureus necrotizing pneumonia because it inhibits the bacterial production of lung-damaging toxins at the site of infection.

scholarly journals Manipulation of Autophagy in Phagocytes Facilitates Staphylococcus aureus Bloodstream Infection

2015 ◽  
Vol 83 (9) ◽  
pp. 3445-3457 ◽  
Author(s):  
Kate M. O'Keeffe ◽  
Mieszko M. Wilk ◽  
John M. Leech ◽  
Alison G. Murphy ◽  
Maisem Laabei ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Systemic Infection ◽  
Critical Factor ◽  
Intracellular Survival ◽  
Autophagic Flux ◽  
Content Type ◽  
Bactericidal Effects ◽  
Staphylococcus Aureus Bloodstream Infection ◽  
Direct Killing

The capacity for intracellular survival within phagocytes is likely a critical factor facilitating the dissemination ofStaphylococcus aureusin the host. To date, the majority of work onS. aureus-phagocyte interactions has focused on neutrophils and, to a lesser extent, macrophages, yet we understand little about the role played by dendritic cells (DCs) in the direct killing of this bacterium. Using bone marrow-derived DCs (BMDCs), we demonstrate for the first time that DCs can effectively killS. aureusbut that certain strains ofS. aureushave the capacity to evade DC (and macrophage) killing by manipulation of autophagic pathways. Strains with high levels of Agr activity were capable of causing autophagosome accumulation, were not killed by BMDCs, and subsequently escaped from the phagocyte, exerting significant cytotoxic effects. Conversely, strains that exhibited low levels of Agr activity failed to accumulate autophagosomes and were killed by BMDCs. Inhibition of the autophagic pathway by treatment with 3-methyladenine restored the bactericidal effects of BMDCs. Using anin vivomodel of systemic infection, we demonstrated that the ability ofS. aureusstrains to evade phagocytic cell killing and to survive temporarily within phagocytes correlated with persistence in the periphery and that this effect is critically Agr dependent. Taken together, our data suggest that strains ofS. aureusexhibiting high levels of Agr activity are capable of blocking autophagic flux, leading to the accumulation of autophagosomes. Within these autophagosomes, the bacteria are protected from phagocytic killing, thus providing an intracellular survival niche within professional phagocytes, which ultimately facilitates dissemination.

scholarly journals Role of BrnQ1 and BrnQ2 in Branched-Chain Amino Acid Transport and Virulence in Staphylococcus aureus

2014 ◽  
Vol 83 (3) ◽  
pp. 1019-1029 ◽  
Author(s):  
Julienne C. Kaiser ◽  
Sameha Omer ◽  
Jessica R. Sheldon ◽  
Ian Welch ◽  
David E. Heinrichs
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Gene ◽  
Defined Medium ◽  
Infection Model ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Branched Chain Amino Acid ◽  
Branched Chain

The branched-chain amino acids (BCAAs; Ile, Leu, and Val) not only are important nutrients for the growth ofStaphylococcus aureusbut also are corepressors for CodY, which regulates virulence gene expression, implicating BCAAs as an important link between the metabolic state of the cell and virulence. BCAAs are either synthesized intracellularly or acquired from the environment.S. aureusencodes three putative BCAA transporters, designated BrnQ1, BrnQ2, and BrnQ3; their functions have not yet been formally tested. In this study, we mutated all threebrnQparalogs so as to characterize their substrate specificities and their roles in growthin vitroandin vivo. We demonstrated that in the community-associated, methicillin-resistantS. aureus(CA-MRSA) strain USA300, BrnQ1 is involved in uptake of all three BCAAs, BrnQ2 transports Ile, and BrnQ3 does not have a significant role in BCAA transport under the conditions tested. Of the three, only BrnQ1 is essential for USA300 to grow in a chemically defined medium that is limited for Leu or Val. Interestingly, we observed that abrnQ2mutant grew better than USA300 in media limited for Leu and Val, owing to the fact that this mutation leads to overexpression ofbrnQ1. In a murine infection model, thebrnQ1mutant was attenuated, but in contrast,brnQ2mutants had significantly increased virulence compared to that of USA300, a phenotype we suggest is at least partially linked to enhancedin vivoscavenging of Leu and Val through BrnQ1. These data uncover a hitherto-undiscovered connection between nutrient acquisition and virulence in CA-MRSA.

scholarly journals Draft Genome Sequence of the Community-Associated Staphylococcus aureus Sequence Type 88 Strain LVP-7, Isolated from an Ocular Infection

2021 ◽  
Vol 10 (7) ◽  
Author(s):  
Savitha Nadig ◽  
Sneha Murthy ◽  
Muralidharan Vandanashree ◽  
Hosahalli S. Subramanya ◽  
Balasubramanian Gopal ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Genome Sequence ◽  
De Novo ◽  
Draft Genome ◽  
Sequence Type ◽  
Draft Genome Sequence ◽  
Ocular Infection ◽  
Content Type ◽  
Type V ◽  
Panton Valentine Leukocidin

ABSTRACT We report a de novo-assembled draft genome sequence of the Indian Staphylococcus aureus sequence type 88 (ST88) strain LVP-7, isolated from an ocular infection. The genome harbors a Panton-Valentine leukocidin phage, a type V staphylococcal cassette chromosome mec element, the delta-hemolysin-converting Newman phage ΦNM3, and the pathogenicity island SaPI3, encoding the superantigen enterotoxin B.

scholarly journals AUC/MIC Pharmacodynamic Target Is Not a Good Predictor of Vancomycin Efficacy in Methicillin-Resistant Staphylococcus aureus Experimental Endocarditis

2017 ◽  
Vol 61 (6) ◽  
Author(s):  
Ximena Castañeda ◽  
Cristina García-de-la-Mària ◽  
Oriol Gasch ◽  
Juan M. Pericas ◽  
Yolanda Armero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Good Predictor ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Area Under The Curve ◽  
Methicillin Resistant ◽  
Bacterial Counts ◽  
Content Type ◽  
Treatment Groups ◽  
Mrsa Strains

ABSTRACT The aim of this in vivo study was to compare the efficacy of vancomycin at standard doses (VAN-SD) to that of VAN at adjusted doses (VAN-AD) in achieving a VAN area under the curve/MIC ratio (AUC/MIC) of ≥400 against three methicillin-resistant Staphylococcus aureus (MRSA) strains with different microdilution VAN MICs in an experimental endocarditis model. The valve vegetation bacterial counts after 48 h of VAN therapy were compared, and no differences were observed between the two treatment groups for any of the three strains tested. Overall, for VAN-SD and VAN-AD, the rates of sterile vegetations were 15/45 (33.3%) and 21/49 (42.8%) (P = 0.343), while the medians (interquartile ranges [IQRs]) for log10 CFU/g of vegetation were 2 (0 to 6.9) and 2 (0 to 4.5) (P = 0.384), respectively. In conclusion, this VAN AUC/MIC pharmacodynamic target was not a good predictor of vancomycin efficacy in MRSA experimental endocarditis.

scholarly journals Efficacy of NZ2114, a Novel Plectasin-Derived Cationic Antimicrobial Peptide Antibiotic, in Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus

2011 ◽  
Vol 55 (11) ◽  
pp. 5325-5330 ◽  
Author(s):  
Yan Q. Xiong ◽  
Wessam Abdel Hady ◽  
Antoine Deslandes ◽  
Astrid Rey ◽  
Laurent Fraisse ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Maximum Effect ◽  
Peptide Antibiotic ◽  
Time Curve ◽  
Cationic Antimicrobial Peptide ◽  
Unbound Fraction ◽  
Methicillin Resistant ◽  
Content Type ◽  
Conventional Antibiotics

ABSTRACTCationic antimicrobial peptides (CAPs) play important roles in host immune defenses. Plectasin is a defensin-like CAP isolated from the saprophytic fungusPseudoplectania nigrella. NZ2114 is a novel variant of plectasin with potent activity against Gram-positive bacteria. In this study, we investigated (i) thein vivopharmacokinetic and pharmacodynamic (PK/PD) characteristics of NZ2114 and (ii) thein vivoefficacy of NZ2114 in comparison with those of two conventional antibiotics, vancomycin or daptomycin, in an experimental rabbit infective endocarditis (IE) model due to a methicillin-resistantStaphylococcus aureus(MRSA) strain (ATCC 33591). All NZ2114 regimens (5, 10, and 20 mg/kg of body weight, intravenously [i.v.], twice daily for 3 days) significantly decreased MRSA densities in cardiac vegetations, kidneys, and spleen versus those in untreated controls, except in one scenario (5 mg/kg, splenic MRSA counts). The efficacy of NZ2114 was clearly dose dependent in all target tissues. At 20 mg/kg, NZ2114 showed a significantly greater efficacy than vancomycin (P< 0.001) and an efficacy similar to that of daptomycin. Of importance, only NZ2114 (in 10- and 20-mg/kg regimens) prevented posttherapy relapse in cardiac vegetations, kidneys, and spleen, while bacterial counts in these target tissues continued to increase in vancomycin- and daptomycin-treated animals. Thesein vivoefficacies were equivalent and significantly correlated with three PK indices investigated:fCmax/MIC (the maximum concentration of the free, unbound fraction of a drug in serum divided by the MIC),fAUC/MIC (where AUC is the area under the concentration-time curve), andf%T>MIC(%T>MICis the cumulative percentage of a 24-h period that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions), as analyzed by a sigmoid maximum-effect (Emax) model (R2> 0.69). The superior efficacy of NZ2114 in this MRSA IE model suggests the potential for further development of this compound for treating serious MRSA infections.

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