Crucial role for central carbon metabolism in the bacterial L-form switch and killing by β-lactam antibiotics

Abstract

The peptidoglycan (PG) cell wall is an essential structure for the growth of most bacteria. However, many are capable of switching into a wall-deficient L-form state, which is resistant to antibiotics that target cell wall synthesis, under osmoprotective conditions, including host environments. L-form cells might have an important role in chronic or recurrent infections. Crucially, the cellular pathways involved in switching to and from the L-form state are still poorly understood. This work shows that the lack of cell wall or blocking its synthesis by β-lactam antibiotics, results in an increased flux through glycolysis. This leads to the production of reactive oxygen species (ROS) from the respiratory chain (RC), which prevents L-form growth. Compensation for the metabolic imbalance by slowing down glycolysis, activating gluconeogenesis, or depleting oxygen, enables L-form growth in Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus. These effects do not occur in Enterococcus faecium, which lacks the RC pathway. Our results collectively show that when cell wall synthesis is blocked under aerobic and glycolytic conditions the perturbation of cellular metabolism causes cell death. We provide a mechanistic framework for many anecdotal descriptions of the optimal conditions for L-form growth and non-lytic killing by β-lactam antibiotics.

Formation of wall-less cells inKitasatospora viridifaciensrequires cytoskeletal protein FilP in oxygen-limiting conditions

“…Notably, L-form bacteria were found to be sensitive to oxidative damage caused by high ROS levels 28 . Counteracting these high amounts of cytotoxic ROS compounds, as by redirecting carbon metabolism, allows the CWD cells to become robust and proliferating L-forms 28,29 . When grown anaerobically, oxygen is not available as electron acceptor in the ETC chain and therefore ROS levels are lower.…”

Constructing and deconstructing the bacterial cell wall

“…It was believed previously that the PBP loss of function was directly bactericidal. PBP inactivation by β‐lactams is seen now as the triggering event that initiates more complex, and perhaps even species‐specific, pathways that culminate in bactericidal cell lysis . Perhaps as a consequence (but at the molecular level, for reasons not understood) some resistance mechanisms against the β‐lactams exert a cellular cost.…”

“…PBP inactivation by β-lactams is seen now as the triggering event that initiates more complex, and perhaps even species-specific, pathways that culminate in bactericidal cell lysis. [115][116][117][118][119][120] Perhaps as a consequence (but at the molecular level, for reasons not understood) some resistance mechanisms against the β-lactams exert a cellular cost. The notorious Grampositive pathogen S. aureus does not activate its resistance mechanisms until it detects the presence of a β-lactam.…”

Outer membrane protein A (OmpA) as a potential therapeutic target for Acinetobacter baumannii infection

“…Generally, there are two ways to design novel antimicrobial agents. The one is to inhibit the production of essential substance for bacteria survival [13,14]; the other is to inhibit virulence factors or antibiotic resistance genes of pathogenic bacteria in order to suppress pathogenicity or improve their sensitivity to antibiotics [15,16]. However, inhibiting single essential component inevitably brings about great evolutionary pressure to bacteria and promotes the development of high-level drug-resistant strains [17].…”