The microbial stress responses of Escherichia coli and Staphylococcus aureus induced by chitooligosaccharide.

Intermediate-state bacteria produced in the process of bacteriostasis have always been a potential threat to public health, but they are very easy to be overlooked. As a natural and non-toxic biological antibacterial agent, chitooligosaccharide (COS) has attracted the public's attention. However, little is known about the microbial stress response during the antibacterial process of COS. In this study, the antibacterial mechanisms of COS were expounded, and the formation of sublethal and viable but nonculturable (VBNC) state were further investigated. The COS was shown to bind to the cell envelopes, and the permeability and integrity of bacterial cell membrane were damaged severely, accompanied by the increase of intracellular reactive oxygen species and decrease of adenosine triphosphate content. Flow cytometry analysis indicated that COS finally inactivated Escherichia coli through the sublethal injury process. While for Staphylococcus aureus, some cells were induced into VBNC state by COS, causing incomplete inactivation.