Staphylococcus aureus is an opportunistic pathogen responsible for a diverse range of human and animal diseases. In particular, methicillin-resistant S. aureus (MRSA) is a major challenge because of the prevalence of antibiotic-resistant strains and the emergence of clinical isolates resistant to vancomycin have made the control of  S. aureus increasingly difficult.1 The emergence of and spread of MRSA is a global problem, and has been shown to be associated with both hospital and community-acquired infections. Indeed, S. aureus possesses an array of virulence factors that permits it to persist in human infections, including the formation of a protective polysaccharide coated cell wall.2 Unfortunately, effective antimicrobial treatment options for infections caused by these pathogens are limited. A promising treatment alternative is noble metal (gold or silver)-drug conjugated nanoparticles that preferentially target pathogens.3 So while this targeting approach could be compromised by future cellular surface phenotypic changes, it is not subject to the broad spectrum efflux pumps believed responsible for much of the current drug resistance mechanisms, and the particles could be retargeted to a different phenotypic feature.  Furthermore, the intrinsic nanoparticle properties of size and shape are of great importance in determining cellular uptake efficiency, circulation time, light absorption and scattering cross-section.  Notably, the absorption cross-section is ~105 higher for gold nanoparticles than for organic dyes and is highly dependent upon the nanoparticle anisotropy.4  Because of the high absorption cross sections for noble metal nanoparticles, the local heating caused by a laser wavelength at the absorption maximum can kill pathogens near these nanoparticles.  This approach termed “plasmonic photo-thermal therapy” (PPTT) is a nascent area of nanobiotechnology.5 Problem Statement. The current research on photon-plasmon interactions have focused on therapeutic applications in the context of PPTT.6-7 However, there is little research on the photon-plasmon interactions that could have important remediation applications. Indeed, a coherent mechanistic understanding of eukaryotic and prokaryotic cell death is missing.8 The thermal heating effect4-5, 9 and the production of the reactive oxygen species (via metal photoelectrons) may be responsible depending on the experimental laser power and nanoparticle concentration

 

 A.W. ARUNI, R.M.E. MCKENZIE.., D.O. OSBOURNE, A.S. MUTHIAH and  H.M. FLETCHER.   Division of Microbiology and Molecular Genetics School of Medicine Loma Linda University, Loma Linda, CA,USA   Porphyromonas gingivalis is an important etiological agent of adult periodontitis.  The survival of P. gingivalis in the inflammatory microenvironment of the periodontal pocket would require an ability to overcome oxidative stress resulting from bactericidal oxygen metabolites generated from occasional exposure to oxygen and polymorphonuclear leukocytes activity.  We have used a global approach to assess the transcription profile of the cellular response of isogenic mutants of P. gingivalis in an environment of oxidative stress typical of the periodontal pocket.  An in silico analysis of the response to hydrogen peroxide-induced oxidative stress identified the expression of several secretory and metabolic pathways. In the wild-type W83 strain, the formaldehyde assimilation, biotin synthesis, folate biosynthesis and transformation pathways were upregulated. In FLL92, a vimA-defective isogenic mutant that is more sensitive to oxidative stress, there was upregulation of alternative energy mechanisms such as glycosylation, protein cleavage, lipid elongation, and fatty acid biosynthesis. There were major variations in the protein transport systems between the two strains.  Several hypothetical proteins that may mediate type III secretion-like properties were upregulated.  In addition, there was an upregulation of the G-protein (PG2143) which in other bacterial systems is known to act as a secondary messenger in the stress mediated pathways of protein transport and elimination oxidative damaged macromolecules. Taken together, it is likely that a hormesis type response could be an alternative mechanism of P. gingivalis survival during oxidative stress.