title: Putrescine reduces antibiotic-induced oxidative stress as a mechanism of modulation of antibiotic resistance in Burkholderia cenocepacia.
abstract: Communication of antibiotic resistance among bacteria via small molecules is implicated in transient reduction of bacterial susceptibility to antibiotics, which could lead to therapeutic failures aggravating the problem of antibiotic resistance. Released putrescine from the extremely antibiotic-resistant bacterium Burkholderia cenocepacia protects less-resistant cells from different species against the antimicrobial peptide polymyxin B (PmB). Exposure of B. cenocepacia to sublethal concentrations of PmB and other bactericidal antibiotics induces reactive oxygen species (ROS) production and expression of the oxidative stress response regulator OxyR. We evaluated whether putrescine alleviates antibiotic-induced oxidative stress. The accumulation of intracellular ROS, such as superoxide ion and hydrogen peroxide, was assessed fluorometrically with dichlorofluorescein diacetate, while the expression of OxyR and putrescine synthesis enzymes was determined in luciferase assays using chromosomal promoter-lux reporter system fusions. We evaluated wild-type and isogenic deletion mutant strains with defects in putrescine biosynthesis after exposure to sublethal concentrations of PmB and other bactericidal antibiotics. Exogenous putrescine protected against oxidative stress induced by PmB and other antibiotics, whereas reduced putrescine synthesis resulted in increased ROS generation and a parallel increased sensitivity to PmB. Of the 3 B. cenocepacia putrescine-synthesizing enzymes, PmB induced only BCAL2641, an ornithine decarboxylase. This study reveals BCAL2641 as a critical component of the putrescine-mediated communication of antibiotic resistance and as a plausible target for designing inhibitors that would block the communication of such resistance among different bacteria, ultimately reducing the window of therapeutic failure in treating bacterial infections.
authors.affiliation: Centre for Human Immunology and Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt.
authors.forename: Omar M
authors.initials: OM
authors.lastname: El-Halfawy
authors.affiliation: Centre for Human Immunology and Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada Centre for Infection and Immunity, Queen's University Belfast, Belfast, United Kingdom m.valvano@qub.ac.uk.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Valvano
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D057508:Burkholderia cenocepacia / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D002262:Carboxy-Lyases / Q000096:biosynthesis / Q000378:metabolism*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009955:Ornithine Decarboxylase / Q000096:biosynthesis / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D011112:Polymyxin B / Q000494:pharmacology*; D011700:Putrescine / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D006861:Hydrogen Peroxide; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase; C021520:lysine decarboxylase; D011112:Polymyxin B; D011700:Putrescine