Labeling of the pathogenic bacterium Staphylococcus aureus with gold or ferric oxide-core nanoparticles highlights new capabilities for investigation of host-pathogen interactions.

Throughout the world, infections caused by bacteria such as Staphylococcus aureus are a major cause of morbidity and mortality. In order to gain some understanding of the complicated physiological link between host and pathogen, modern techniques such as confocal microscopy and sophisticated OMICs technologies are suitable. However, labeling of pathogens such as S. aureus with green fluorescent protein, for example, or the generation of a reliable antibody, which are prerequisites for the application of reproducible isolation techniques, does not always succeed. Here, we present a universal approach for monitoring pathogen traffic after internalization into host cells by fluorescence microscopy and for isolation of bacteria from host-pathogen interaction assays using gold or ferric oxide-core, poly(vinyl alcohol) coated, and fluorescence-labeled nanoparticles (NP). The incubation of S. aureus HG001 with those NP had only minor effects on the bacterial growth in vitro. Quantitative proteome analysis after 24 h of NP incubation revealed that presence of NP provoked only marginal changes in the proteome pattern. The method presented enabled us to investigate the behavior of S. aureus HG001 during infection of S9 human epithelial cells by means of fluorescence microscopy and proteomics using magnetic separation or cell sorting.