Beta-Lactamase Repressor BlaI Modulates Staphylococcus aureus Cathelicidin Antimicrobial Peptide Resistance and Virulence.

BlaI is a repressor of BlaZ, the beta-lactamase responsible for penicillin resistance in Staphylococcus aureus. Through screening a transposon library in S. aureus Newman for susceptibility to cathelicidin antimicrobial peptide, we discovered BlaI as a novel cathelicidin resistance factor. Additionally, through integrational mutagenesis in S. aureus Newman and MRSA Sanger 252 strains, we confirmed the role of BlaI in resistance to human and murine cathelidicin and showed that it contributes to virulence in human whole blood and murine infection models. We further demonstrated that BlaI could be a target for innate immune-based antimicrobial therapies; by removing BlaI through subinhibitory concentrations of 6-aminopenicillanic acid, we were able to sensitize S. aureus to LL-37 killing

Bactericidal Kinetics of Marine-Derived Napyradiomycins against Contemporary Methicillin-Resistant Staphylococcus aureus

There is an urgent need for new antibiotics to treat hospital- and community-associated methicillin-resistant Staphylococcus aureus (MRSA) infections. Previous work has indicated that both terrestrial and marine-derived members of the napyradiomycin class possess potential anti-staphylococcal activities. These compounds are unique meroterpenoids with unusual levels of halogenation. In this paper we report the evaluation of two previously described napyradiomycin derivatives, A80915A (1) and A80915B (2) produced by the marine-derived actinomycete, Streptomyces sp. strain CNQ-525, for their specific activities against contemporary and clinically relevant MRSA. Reported are studies of the in vitro kinetics of these chemical scaffolds in time-kill MRSA assays. Both napyradiomycin derivatives demonstrate potent and rapid bactericidal activity against contemporary MRSA strains. These data may help guide future development and design of analogs of the napyradiomycins that could potentially serve as useful anti-MRSA therapeutics

Anthracimycin activity against contemporary methicillin-resistant Staphylococcus aureus.

Anthracimycin is a recently discovered novel marine-derived compound with activity against Bacillus anthracis. We tested anthracimycin against an expanded panel of Staphylococcus aureus strains in vitro and in vivo. All strains of S. aureus tested, including methicillin-susceptible, methicillin-resistant (MRSA) and vancomycin-resistant strains of S. aureus, were susceptible to anthracimycin at MIC values of ⩽0.25 mg l(-1). Although its postantibiotic effects were minimal, anthracimycin exhibited potent and rapid bactericidal activity, with a >4-log kill of USA300 MRSA within 3 h at five times its MIC. At concentrations significantly below the MIC, anthracimycin slowed MRSA growth and potentiated the bactericidal activity of the human cathelicidin, LL-37. The bactericidal activity of anthracimycin was somewhat mitigated in the presence of 20% human serum, and the compound was minimally toxic to human cells, with an IC50 (inhibitory concentration 50)=70 mg l(-1) against human carcinoma cells. At concentrations near the MIC, anthracimycin inhibited S. aureus nucleic acid synthesis as determined by optimized macromolecular synthesis methodology, with inhibition of DNA and RNA synthesis occurring in the absence of DNA intercalation. Anthracimycin at a single dose of 1 or 10 mg kg(-1) was able to protect mice from MRSA-induced mortality in a murine peritonitis model of infection. Anthracimycin provides an interesting new scaffold for future development of a novel MRSA antibiotic

Marinopyrrole Derivatives as Potential Antibiotic Agents against Methicillin-Resistant Staphylococcus aureus (I)

Infections caused by drug-resistant pathogens are on the rise. The ongoing spread of methicillin-resistant Staphylococcus aureus (MRSA) strains exemplifies the urgent need for new antibiotics. The marine natural product, marinopyrrole A, was previously shown to have potent antibiotic activity against Gram-positive pathogens, including MRSA. However, its minimum inhibitory concentration (MIC) against MRSA was increased by >500 fold in the presence of 20% human serum, thus greatly limiting therapeutic potential. Here we report our discovery of a novel derivative of marinopyrrole A, designated 1a, featuring a 2–4 fold improved MIC against MRSA and significantly less susceptibility to serum inhibition. Importantly, compound 1a displayed rapid and concentration-dependent killing of MRSA. Compared to the natural product counterpart, compound 1a provides an important natural product based scaffold for further Structure Activity Relationship (SAR) and optimization

Imaging mass spectrometry of intraspecies metabolic exchange revealed the cannibalistic factors of Bacillus subtilis

During bacterial cannibalism, a differentiated subpopulation harvests nutrients from their genetically identical siblings to allow continued growth in nutrient-limited conditions. Hypothesis-driven imaging mass spectrometry (IMS) was used to identify metabolites active in a Bacillus subtilis cannibalism system in which sporulating cells lyse nonsporulating siblings. Two candidate molecules with sequences matching the products of skfA and sdpC, genes for the proposed cannibalistic factors sporulation killing factor (SKF) and sporulation delaying protein (SDP), respectively, were identified and the structures of the final products elucidated. SKF is a cyclic 26-amino acid (aa) peptide that is posttranslationally modified with one disulfide and one cysteine thioether bridged to the α-position of a methionine, a posttranslational modification not previously described in biology. SDP is a 42-residue peptide with one disulfide bridge. In spot test assays on solid medium, overproduced SKF and SDP enact a cannibalistic killing effect with SDP having higher potency. However, only purified SDP affected B. subtilis cells in liquid media in fluorescence microscopy and growth assays. Specifically, SDP treatment delayed growth in a concentration-dependent manner, caused increases in cell permeability, and ultimately caused cell lysis accompanied by the production of membrane tubules and spheres. Similarly, SDP but not SKF was able to inhibit the growth of the pathogens Staphylococcus aureus and Staphylococcus epidermidis with comparable IC(50) to vancomycin. This investigation, with the identification of SKF and SDP structures, highlights the strength of IMS in investigations of metabolic exchange of microbial colonies and also demonstrates IMS as a promising approach to discover novel biologically active molecules

A battle with superbugs : New compounds and targets against drug-resistant pathogens

Drug-resistant pathogens throughout the world, in first and third world countries, create a continual burden on public health. With global emergence of multiply-drug resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and parasites like Plasmodium falciparum, there is a distinct need for the development of novel anti-infectives to target these infections. Our data encompasses interdisciplinary links between pharmacology, natural product chemistry, infectious disease pathogenesis and innate immunity. We have (I) characterized novel antibiotics as new classical-type antibiotics, (II) identified a significant virulence factor, alpha-toxin, in MRSA and characterized its potential as a therapeutic target and (III) investigated a pathogen-specific cAMP-dependent protein kinase (PKA) regulatory subunit as a possible therapeutic target in the treatment of P. falciparum. From this multi-dimensional approach, we have identified potent antibacterial therapies. Our data highlights the ocean as an extremely rich resource of chemically diverse scaffolds. Here, we comprehensively characterize four marine-derived chemical scaffolds, marinopyrrole, napyradiomycin, etamycin and nosiheptide for their potent antibacterial activities against contemporary strains of multi-drug resistant MRSA. Further, in this work, we identify a potential MRSA virulence factor inhibitor. Diflunisal, a known and commonly used non-steroidal anti-inflammatory agent, was predicted via virtual screening to inhibit the production of a pore-forming S. aureus toxin. Our data emphasizes the potent anti-virulence properties of diflunisal and identifies a wide range of supplementary anti-bacterial and anti-virulence properties that could prove extremely useful in treating virulent and pathogenic MRSA infections. Finally, we investigate the PKA regulatory subunit of P. falciparum to identify pathogen-specific features that may be implicated in its roles in malarial parasite development, host invasion and pathogenesis. We conclude it to be a valid therapeutic target by identifying species-specific differences parasitic and mammalian isoforms that may prove useful in the development and engineering of therapeutic inhibitors. This work highlights three novel approaches to anti- pathogen research where we pinpoint valid therapeutic targets and potential therapies in the ongoing battle against emerging superbug

A battle with superbugs : New compounds and targets against drug-resistant pathogens

Drug-resistant pathogens throughout the world, in first and third world countries, create a continual burden on public health. With global emergence of multiply-drug resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and parasites like Plasmodium falciparum, there is a distinct need for the development of novel anti-infectives to target these infections. Our data encompasses interdisciplinary links between pharmacology, natural product chemistry, infectious disease pathogenesis and innate immunity. We have (I) characterized novel antibiotics as new classical-type antibiotics, (II) identified a significant virulence factor, alpha-toxin, in MRSA and characterized its potential as a therapeutic target and (III) investigated a pathogen-specific cAMP-dependent protein kinase (PKA) regulatory subunit as a possible therapeutic target in the treatment of P. falciparum. From this multi-dimensional approach, we have identified potent antibacterial therapies. Our data highlights the ocean as an extremely rich resource of chemically diverse scaffolds. Here, we comprehensively characterize four marine-derived chemical scaffolds, marinopyrrole, napyradiomycin, etamycin and nosiheptide for their potent antibacterial activities against contemporary strains of multi-drug resistant MRSA. Further, in this work, we identify a potential MRSA virulence factor inhibitor. Diflunisal, a known and commonly used non-steroidal anti-inflammatory agent, was predicted via virtual screening to inhibit the production of a pore-forming S. aureus toxin. Our data emphasizes the potent anti-virulence properties of diflunisal and identifies a wide range of supplementary anti-bacterial and anti-virulence properties that could prove extremely useful in treating virulent and pathogenic MRSA infections. Finally, we investigate the PKA regulatory subunit of P. falciparum to identify pathogen-specific features that may be implicated in its roles in malarial parasite development, host invasion and pathogenesis. We conclude it to be a valid therapeutic target by identifying species-specific differences parasitic and mammalian isoforms that may prove useful in the development and engineering of therapeutic inhibitors. This work highlights three novel approaches to anti- pathogen research where we pinpoint valid therapeutic targets and potential therapies in the ongoing battle against emerging superbug