Targeting NAD+ regeneration enhances antibiotic susceptibility of Streptococcus pneumoniae during invasive disease

Glutathione reductase modulates endogenous oxidative stress and affects growth and virulence in Avibacterium paragallinarum

Glutathione reductase (GR) plays a pivotal role in managing oxidative stress, a process crucial for microbial virulence and adaptation, yet it has not been extensively explored in bacteria such as Avibacterium paragallinarum (Av. paragallinarum). This study examined the specific roles of GR in Av. paragallinarum, focusing on how GR modulates the bacterium's response to oxidative stress and impacts its pathogenic behavior. Using gene knockouts together with transcriptomic and metabolomic profiling, we identified an important shift in redox balance due to GR deficiency, which disrupted energy metabolism and weakened the oxidative stress defense, culminating in a notable decline in virulence. In addition, decreased growth rates, reduced biofilm production, and weakened macrophage interactions were observed in GR-deficient strains. Notably, our findings reveal a sophisticated adaptation mechanism wherein the bacterium recalibrated its metabolic pathways in response to GR deficiency without fully restoring virulence. Our in vivo studies further highlight the pivotal role of GR in pathogen fitness. Together, our findings connect GR-mediated redox control to bacterial virulence, thereby furthering the understanding of microbial adaptation and positioning GR as a potential antimicrobial target. Our insights into the GR-centric regulatory network pave the way for leveraging bacterial redox mechanisms in the development of novel antimicrobial therapies, highlighting the importance of oxidative stress management in bacterial pathogenicity.

Streptococcus pneumoniae favors tolerance via metabolic adaptation over resistance to circumvent fluoroquinolones

Streptococcus pneumoniae is a major human pathogen of global health concern and the rapid emergence of antibiotic resistance poses a serious public health problem worldwide. Fluoroquinolone resistance in S. pneumoniae is an intriguing case because the prevalence of fluoroquinolone resistance does not correlate with increasing usage and has remained rare. Our data indicate that deleterious fitness costs in the mammalian host constrain the emergence of fluoroquinolone resistance both by de novo mutation and recombination. S. pneumoniae was able to circumvent such deleterious fitness costs via the development of antibiotic tolerance through metabolic adaptation that reduced the production of reactive oxygen species, resulting in a fitness benefit during infection of mice treated with fluoroquinolones. These data suggest that the emergence of fluoroquinolone resistance is tightly constrained in S. pneumoniae by fitness tradeoffs and that mutational pathways involving metabolic networks to enable tolerance phenotypes are an important contributor to the evasion of antibiotic-mediated killing.IMPORTANCEThe increasing prevalence of antibiotic resistant bacteria is a major global health concern. While many species have the potential to develop antibiotic resistance, understanding the barriers to resistance emergence in the clinic remains poorly understood. A prime example of this is fluroquinolone resistance in Streptococcus pneumoniae, whereby, despite continued utilization, resistance to this class of antibiotic remains rare. In this study, we found that the predominant pathways for developing resistance to this antibiotic class severely compromised the infectious capacity of the pneumococcus, providing a key impediment for the emergence of resistance. Using in vivo models of experimental evolution, we found that S. pneumoniae responds to repeated fluoroquinolone exposure by modulating key metabolic pathways involved in the generation of redox molecules, which leads to antibiotic treatment failure in the absence of appreciable shifts in resistance levels. These data underscore the complex pathways available to pathogens to evade antibiotic mediating killing via antibiotic tolerance.

From bacteria to biomedicine: Developing therapies exploiting NAD+ metabolism

Nicotinamide adenine dinucleotide (NAD+) serves as a critical cofactor in cellular metabolism and redox reactions. Bacterial pathways rely on NAD+ participation, where its stability and concentration govern essential homeostasis and functions. This review delves into the role and metabolic regulation of NAD+ in bacteria, highlighting its influence on physiology and virulence. Notably, we explore enzymes linked to NAD+ metabolism as antibacterial drug targets and vaccine candidates. Moreover, we scrutinize NAD+'s medical potential, offering insights for its application in biomedicine. This comprehensive assessment informs future research directions in the dynamic realm of NAD+ and its biomedical significance.