Dormant Cells of Staphylococcus aureus Are Resuscitated by Spent Culture Supernatant

We describe the first in vitro model of dormancy in Staphylococcus aureus, showing that cells are generated which can beresuscitated by addition of spent medium supernatant taken from cultures of the same organism. Over 30 days, culturablecounts in dormant cultures of S. aureus SH1000 fell from 106–107 cfu/ml to ,10 cfu/ml as measured by the Most ProbableNumber method in liquid culture, while total counts as determined by microscopy, and supported by data from RT-qPCR,remained around 106–107 cells/ml. Supplementing cultures with 25–50% spent medium resulted in a .600-fold increase inbacterial growth. Resuscitation was a specific effect, greatly reduced by boiling or addition of trypsin to the spentsupernatant. Supernatant also effected a reduction in lag phase of dormant cultures. SEM demonstrated the presence ofsmall coccoid cells in dormant cultures. The results are similar to those seen with resuscitation promoting factors (Rpfs) inactinobacteria. This is the first time resuscitation has been demonstrated in Staphylococcus aureus, which is an importanthuman pathogen. A better understanding of control and reactivation of dormant cells could lead to major improvements inmanaging staphylococcal infections; resuscitation could be an important step in restoring susceptibility to antibiotictreatment