Application of microbial chip for amperometric detection of metabolic alteration in bacteria

The microbial chip of 3.5 nL-volume of collagen gel matrixes entrapping the bacterial cells in living state has been applied to investigate the bacterial response to high osmotic stress. Scanning electrochemical microscopy (SECM) was used to monitor the Fe(CN)64− production that reflects the electron flow at respiratory chain located within the cytoplasmic membrane of bacteria. In the present study, we have found that the ferricyanide reduction activity in the Staphylococcus aureus, osmotolerant bacteria, is enhanced in the presence of highly concentrated salts. This result suggests that the osmotic stress causes the change in membrane structure or membrane-associated protein profile so as to enhance the cell membrane permeability to hydrophilic mediator. The low current responsibility of S. aureus can be improved not only by (1) using hydrophobic mediator, such as quinone derivatives instead of Fe(CN)63− but also (2) exposing S. aureus cells to high osmotic stress in the presence of hydrophilic mediator.