Abstract
Staphylococcus epidermidis biofilm cells can enter a physiological state known as viable but non-culturable (VBNC), where, despite being alive, they do not grow in conventional laboratory media. As such, the presence of VBNC cells impacts the diagnosis of S. epidermidis biofilm-associated infections. Previous transcriptomics analysis of S. epidermidis strain 9142 biofilms with higher proportions of VBNC cells suggested that the genes pdhA, codY and mazEF could be involved in the induction of the VBNC state. However, it was previously demonstrated that VBNC induction is strain-dependent. To properly assess the role of these genes in VBNC induction, the construction of mutant strains is necessary. Thus, herein, we assessed if VBNC cells could be induced in strain 1457, a strain amenable to genetic manipulation, and if the previously identified genes were involved in the modulation of the VBNC state in this strain. Furthermore, we evaluated the formation of VBNC cells on planktonic cultures. Our results showed that despite being commonly associated with biofilms, the proportion of VBNC cells can be modulated in both biofilm and planktonic cultures and that the expression of codY and pdhA was upregulated under VBNC inducing conditions in both phenotypes. Overall, our study revealed that the formation of VBNC cells in S. epidermidis is independent of the mode of growth and that the genes codY and pdhA seem to be relevant for the regulation of this physiological condition.
Highlights
Staphylococcus epidermidis is considered an opportunistic pathogen responsible for many healthcare-associated infections, mainly those related to biofilm formation on indwelling medical devices (Mack et al, 2013)
To assess if the previously described viable but non-culturable (VBNC) induction model could be used in strain 1457, we first compared the total amount of cells, the number of living cells and the number of culturable cells
Our results showed that the supplementation of the culture medium with 1% glucose induced a reduction in 1457 biofilm cells culturability of about 70% when compared to biofilms grown in media supplemented with 1% glucose plus 20 mM MgCl2
Summary
Staphylococcus epidermidis is considered an opportunistic pathogen responsible for many healthcare-associated infections, mainly those related to biofilm formation on indwelling medical devices (Mack et al, 2013). S. epidermidis VBNC Cells primarily associated with the poor capacity to eradicate biofilms, which are known to have bacterial cells with distinct physiological states (Rani et al, 2007), including viable but non-culturable (VBNC) cells (Cerca et al, 2011a; Zhang et al, 2018; Li et al, 2020). VBNC cells cannot grow on standard growth media, these cells present a reduced metabolic activity, replication rate and gene transcription (Lleo et al, 2000; Zhang et al, 2018). For this reason, their detection with traditional culture-based methods and, the diagnosis of S. epidermidis biofilm-related infections is hindered (Zandri et al, 2012). The study of the mechanisms underlying the development of this physiological state in S. epidermidis is of utmost importance
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