Autocrine peptides inhibited the formation of VBNC state of Staphylococcus aureus.

Viable but non-culturable (VBNC) Staphylococcus aureus cannot form colonies on a medium, causing a false negative result in culture-based detection, which is a potential hazard to human health. In this study, four peptides (PVSS.a-1, PVSS.a-2, PVSS.a-3, and PVSS.a-4) were identified in the suspension of S. aureus during the VBNC state induction. Notably, PVSS.a-1 and PVSS.a-2 prolonged the entry of S. aureus into the VBNC state in citric acid solution (pH 4.0) at 4℃ by 83 % and 103 %, respectively. Such a delaying effect indicates that S. aureus might be forced to enter the VBNC state under pressure, rather than actively. Microscopic observation and zeta-potential determination suggested that PVSS.a-1 and PVSS.a-2 improved the aggregation of S. aureus cells. Furthermore, the two peptides were demonstrated to enter cells by FITC-label localization detection, and changed internal structures and improved intracellular enzyme activities occurred in the two peptide-treated cells. Through the analysis of interactions with DNA and proteins of S. aureus, it was found that PVSS.a-1 and PVSS.a-2 might affect cellular processes, including cell division, transcription, translation, and material and energy metabolisms. These alterations improved the viability and culturability of S. aureus, thereby delaying VBNC formation. In summary, our study reveals how autocrine peptides delay VBNC formation of S. aureus, and provides a new insight into the real intention of bacteria to form VBNC state under adverse conditions.