Hawas, S. | Search bioRxiv

bioRxiv2022

Bladder-draining lymph nodes support germinal centre B cell responses during urinary tract infection in mice

Bacterial urinary tract infections (UTIs) are both common and exhibit high recurrence rates in women. UTI healthcare costs are increasing due to the rise of multi-drug resistant (MDR) bacteria, necessitating alternative approaches for infection control. Here, we investigated whether host adaptive immune responses can influence infection outcomes. We employed a mouse model in which wild-type C57BL/6J mice were transurethrally inoculated with an MDR UTI strain of uropathogenic Escherichia coli (UPEC). Firstly, we noted that rag1-/- C57BL/6J mice harboured larger bacterial burdens than wild-type counterparts, consistent with a role for T and/or B cells in optimal control of UTI. Consistent with this, UTI triggered in the bladders of wild-type mice early increases of myeloid cells, including CD11chi conventional dendritic cells, suggesting possible involvement of these professional antigen-presenting cells. Importantly, germinal centre (GC) B cell responses developed by 4 weeks post-infection in bladder-draining lymph nodes of wild-type mice, and although modest in magnitude and transient in nature, could not be boosted with a second UTI. Thus, our data reveal for the first time in a mouse model, that Gram-negative bacterial UTI induces local B cell immune responses in bladder-draining lymph nodes, which could potentially serve to control infection.

immunology↗

bioRxiv2022

Loss of β-ketoacyl acyl carrier protein synthase III activity restores multidrug-resistant Escherichia coli sensitivity to previously ineffective antibiotics

Antibiotic resistance is one of the most prominent threats to modern medicine. In the latest World Health Organization list of bacterial pathogens that urgently require new antibiotics, nine out of 12 are Gram-negative, with four being of Critical Priority. One crucial barrier restricting antibiotic efficacy against Gram-negative bacteria is their unique cell envelope. While fatty acids are a shared constituent of all structural membrane lipids, their biosynthesis pathway in bacteria is distinct from eukaryotes making it an attractive target for new antibiotic development that remains less explored. Here, we interrogated the redundant components of the bacterial Type II Fatty Acid Synthesis (FAS II) pathway, showing that disrupting FAS II homeostasis in Escherichia coli through deletion of the fabH gene damages the cell envelope of antibiotic susceptible and antibiotic resistant clinical isolates. The fabH gene encodes the {beta}-ketoacyl acyl carrier protein synthase III (KAS III), which catalyzes the initial condensation reactions during fatty acid biosynthesis. We show that fabH null mutation potentiated the killing of multi-drug resistant E. coli by a broad panel of previously ineffective antibiotics, despite the presence of relevant antibiotic resistance determinants, for example, carbapenemase kpc2. Enhanced antibiotic sensitivity was additionally demonstrated in the context of eradicating established biofilms and treating established human cell infection in vitro. Our findings showcase the potential of FabH as a promising target that could be further explored in the development of therapies that may repurpose currently ineffective antibiotics or rescue failing last-resort antibiotics against Gram-negative pathogens. IMPORTANCEGram-negative pathogens are a major concern for global public health due to increasing rates of antibiotic resistance and the lack of new drugs. A major contributing factor towards antibiotic resistance in Gram-negative bacteria is their formidable outer membrane, which acts as a permeability barrier preventing many biologically active antimicrobials from reaching the intracellular targets and thus limiting their efficacy. Fatty acids are the fundamental building blocks of structural membrane lipids and their synthesis constitutes an attractive antimicrobial target as it follows distinct pathways in prokaryotes and eukaryotes. Herein, we identified a component of fatty acid synthesis, FabH, as a gate-keeper of outer membrane barrier function. Without FabH, Gram-negative bacteria become susceptible to otherwise impermeable antibiotics and are re-sensitised to killing by last-resort antibiotics. This study supports FabH as a promising target for inhibition in future antimicrobial therapies.

microbiology↗