Loss of GdpP Function in Staphylococcus aureus Leads to β-Lactam Tolerance and Enhanced Evolution of β-Lactam Resistance

Abstract

Infections caused by Staphylococcus aureus are a leading cause of mortality. Treating infections caused by S. aureus is difficult due to resistance against most traditional antibiotics, including β-lactams. We previously reported the presence of mutations in gdpP among S. aureus strains that were obtained by serial passaging in β-lactam drugs. Similar mutations have recently been reported in natural S. aureus isolates that are either non-susceptible or resistant to β-lactam antibiotics. gdpP codes for a phosphodiesterase that cleaves cyclic-di-AMP (CDA), a newly discovered second messenger. In this study, we sought to identify the role of gdpP in β-lactam resistance in S. aureus . Our results showed that gdpP associated mutations caused loss of phosphodiesterase function, leading to increased CDA accumulation in the bacterial cytosol. Deletion of gdpP led to an enhanced ability of the bacteria to withstand a β-lactam challenge (two to three log increase in bacterial colony forming units) by promoting tolerance without enhancing MICs of β-lactam antibiotics. Our results demonstrated that increased drug tolerance due to loss of GdpP function can provide a selective advantage in acquisition of high-level β-lactam resistance. Loss of GdpP function thus increases tolerance to β-lactams that can lead to its therapy failure and can permit β-lactam resistance to occur more readily.

In-vivo detection of cyclic-di-AMP in Staphylococcus aureus

“…Recent studies have demonstrated that CDA plays important roles in regulating vital biological processes such as DNA repair, ion homeostasis, and central carbon metabolism among others (2)(3)(4)(5). In addition, CDA has also been implicated in controlling processes that are important for bacterial pathogenesis such as biofilm formation, antibiotic tolerance, and virulence (6)(7)(8)(9)(10). CDA mediates its function through binding to its cognate effectors (i.e.…”

“…Recent studies have highlighted that increased CDA concentrations promote tolerance to β-lactam antibiotics and allow cell wall restructuring (8,11). Furthermore, a growing number of contemporary clinical surveillance studies have identified mutations in gdpP among β-lactam resistant or non-susceptible natural isolates of S. aureus (12)(13)(14)(15).…”

“…Furthermore, a growing number of contemporary clinical surveillance studies have identified mutations in gdpP among β-lactam resistant or non-susceptible natural isolates of S. aureus (12)(13)(14)(15). Since many of these mutations have been either shown (8) or are predicted to attenuate the function of GdpP, causing increased CDA concentrations in cells, these findings underscored the clinical importance of CDA and highlighted the importance of accurate determination of its concentrations for both basic and clinical research settings.…”

“…In Staphylococcus aureus , CDA synthesis and degradation are mediated by DacA (diadenylate cyclase) and GdpP (the primary CDA phosphodiesterase) respectively (1). Recent studies have highlighted that increased CDA concentrations promote tolerance to β-lactam antibiotics and allow cell wall restructuring (8, 11). Furthermore, a growing number of contemporary clinical surveillance studies have identified mutations in gdpP among β-lactam resistant or non-susceptible natural isolates of S. aureus (12–15).…”

“…The resultant biosensors were cloned into a constitutive expression vector and transformed into a wild-type (Wt) S. aureus and its isogenic Δ gdpP strain. While both the biosensors were able to report the higher level of CDA that is characteristic of a Δ gdpP strain (8), bsuO P6-4 showed significantly enhanced fluorescence compared to that of yuaA P1-4. More importantly, bsuO P6-4 compared to yuaA P1-4 displayed a higher dynamic range of signal (3.73X vs 1.55X) between Wt and Δ gdpP strains making it amenable for detection of a wider concentration range of CDA (Fig.1D).…”