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 superbugs

The marine natural product, marinopyrrole A (1), was previously shown to have significant antibiotic activity against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Although compound (1) exhibits a significant reduction in MRSA activity in the presence of human serum, we have identified key modifications that partially restore activity. We previously reported our discovery of a chloro-derivative of marinopyrrole A (1a) featuring a 2-4 fold improved minimum inhibitory concentration (MIC) against MRSA, significantly less susceptibility to serum inhibition and rapid and concentration-dependent killing of MRSA. Here, we report a novel fluoro-derivative of marinopyrrole A (1e) showing an improved profile of potency, less susceptibility to serum inhibition, as well as rapid and concentration-dependent killing of MRSA.

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.

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.