Project description:The emergence of colistin resistance in carbapenem-resistant and extended-spectrum ß-lactamase (ESBL)-producing bacteria is a significant threat to human health, and new treatment strategies are urgently required. Here we investigated the ability of the safe-for-human use ionophore PBT2 to restore antibiotic sensitivity in several polymyxin-resistant, ESBL-producing, carbapenem resistant Gram-negative human pathogens. PBT2 was observed to resensitize Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa to last-resort polymyxin class antibiotics, including a ‘next generation’ polymyxin derivative, FADDI-287. To gain additional insight into the potential mechanism of action of PBT2, we analyzed the transcriptome of K. pneumoniae and E. coli in the presence of sub-inhibitory concentrations of PBT2. Treatment with PBT2 was associated with multiple stress responses in both K. pneumoniae and E. coli. Significant changes in the transcription of transition metal ion homeostasis genes were observed in both strains.
Project description:We used TraDIS-Xpress to determine the mechanism of action of a novel antimicrobial compound. We found that it inhibits lipid IVA biosynthesis in both Escherichia coli and Salmonella enterica serovar Typhimurium. We also were able to determine mechanisms of synergy with colistin, through ATP biosynthesis and the BasSR signalling system.
Project description:Acinetobacter baumannii is often highly resistant to multiple antimicrobials, posing a risk of treatment failure, and colistin is a "last resort" for treatment of the bacterial infection. However, colistin resistance is easily developed when the bacteria are exposed to the drug, and a comprehensive analysis of colistin-mediated changes in colistin-susceptible and -resistant A. baumannii is needed. In this study, using an isogenic pair of colistin-susceptible and -resistant A. baumannii isolates, alterations in morphologic and transcriptomic characteristics associated with colistin resistance were revealed. Whole-genome sequencing showed that the resistant isolate harbored a PmrBL208F mutation conferring colistin resistance, and all other single-nucleotide alterations were located in intergenic regions. Using scanning electron microscopy, it was determined that the colistin-resistant mutant had a shorter cell length than the parental isolate, and filamented cells were found when both isolates were exposed to the inhibitory concentration of colistin. When the isolates were treated with inhibitory concentrations of colistin, more than 80% of the genes were upregulated, including genes associated with antioxidative stress response pathways. The results elucidate the morphological difference between the colistin-susceptible and -resistant isolates and different colistin-mediated responses in A. baumannii isolates depending on their susceptibility to this drug.
Project description:Here we report the results of a study comparing the global transcriptional responses of Escherichia coli to two well-studied CAMPs, LL37 and colistin, and two ceragenins with related structures, CSA13 and CSA131. We found that E. coli responds similarly to both CAMPs and ceragenins by inducing a Cpx envelope stress response. However, whereas E. coli exposed to CAMPs increased expression of genes involved in colanic acid biosynthesis, bacteria exposed to ceragenins specifically modulated functions related to phosphate transport, indicating distinct mechanisms of action between these two classes of molecules. Overall, this study suggests that while some bacterial responses to ceragenins overlap with those induced by naturally-occurring CAMPs, these synthetic molecules target the bacterial envelope using a distinctive mode of action.