Nanoparticles: The small size of nanoparticles makes them easy to deliver, while their high surface area-to-volume ratio allows them to deliver drugs effectively. Surface modification of nanoparticles can be used to tailor them for specific targets and locations, and the surface chemistry and composition control the timing of activity, drug release, and of duration of action. In addition, alteration of the morphologies of nanoparticles also alters their aggregation, movement, and persistence. All of these properties increase the attractiveness of nanoparticles as antimicrobial agents. Changes in composition can allow nanoparticle-bound drugs to evade or reduce drug resistance mechanisms; for example, poly(co-lactic acid-glycolic acid) (PLGA) nanoparticles containing metronidazole were as effective against juvenile periodontitis as tetracycline, though metronidazole was previously found to be ineffective against the contributing bacterium Aggregibacter actinomycetecomitans. LGA or polyamide (PAMAM) nanoparticles containing platensimycin were more effective against S. aureus in mice than free platensimycin and were even effective against MRSA in mice. PLGA nanoparticles containing azithromycin showed improved activity against MRSA and Enterococcus faecalis, but not Pseudomonas aeruginosa; improvement corresponded to the presence of efflux pump-derived resistance as nanoparticle encapsulated antibiotics are reported to bypass the efflux activity in bacteria . Metal or alloy nanoparticles can also be effective antibacterial agents. Silver nanoparticles have been used to prevent bacterial growth and treat infections, but their toxicity may limit their use. Copper nanoparticles also show antimicrobial activity as well. 352