Ransegnola, B. | Search bioRxiv

bioRxiv2019

A multifaceted cellular damage repair and prevention pathway promotes high level tolerance to β-lactam antibiotics

Bactericidal antibiotics are powerful agents due to their ability to convert essential bacterial functions into lethal processes. However, many important bacterial pathogens are remarkably tolerant against bactericidal antibiotics due to inducible damage repair responses. The cell wall damage response two-component system VxrAB of the gastrointestinal pathogen Vibrio cholerae promotes high-level {beta}-lactam tolerance and controls a gene network encoding highly diverse functions, including negative control over multiple iron uptake systems. How this system contributes to tolerance is poorly understood. Here, we show that {beta}-lactam antibiotics cause an increase in intracellular free iron levels and collateral oxidative damage, which is exacerbated in the {Delta}vxrAB mutant. Mutating major iron uptake systems drastically increased {Delta}vxrAB tolerance to {beta}-lactams. We propose that VxrAB reduces antibiotic-induced toxic iron and concomitant metabolic perturbations by downregulating iron uptake transporters and show that iron sequestration enhances tolerance against {beta}-lactam therapy in a mouse model of cholera infection. Our results suggest that a microorganisms ability to counteract diverse antibiotic-induced stresses promotes high-level antibiotic tolerance, and highlights the complex secondary responses elicited by antibiotics.

microbiology↗

bioRxiv2019

Spheroplast-mediated carbapenem tolerance in Gram-negative pathogens

Antibiotic tolerance, the ability to temporarily sustain viability in the presence of bactericidal antibiotics, constitutes an understudied, yet likely widespread cause of antibiotic treatment failure. We have previously shown that the Gram-negative pathogen Vibrio cholerae is able to tolerate exposure to the typically bactericidal {beta}-lactam antibiotics by assuming a spherical morphotype devoid of detectable cell wall material. However, it is unclear how widespread tolerance is. Here, we have tested a panel of clinically significant Gram-negative pathogens for their response to the potent, broad-spectrum carbapenem antibiotic meropenem. We show that clinical isolates of Enterobacter cloacae, Klebsiella pneumoniae, and Klebsiella aerogenes, but not Escherichia coli, exhibit moderate to high levels of tolerance to meropenem, both in laboratory growth medium and in human serum. Importantly, tolerance was mediated by cell wall-deficient spheroplasts, which readily recovered to wild-type morphology and exponential growth upon removal of antibiotic. Our results suggest that carbapenem tolerance is prevalent in clinically significant bacterial species, and we suggest that this could contribute to treatment failure associated with these organisms.

microbiology↗