Baumannii AB5075 Research Articles

In Vivo Cross-Linking MS Reveals Conservation in OmpA Linkage to Different Classes of β-Lactamase Enzymes.

Molecular interactions between two different classes of β-lactamase enzymes and outer membrane protein A (OmpA) were studied by in vivo chemical cross-linking of a multi-drug-resistant strain of Acinetobacter baumannii AB5075. Class A β-lactamase blaGES-11 and Class D β-lactamase Oxa23, responsible for hydrolysis of different types of β-lactam antibiotics, were found to be cross-linked to similar lysine sites of the periplasmic domain of outer membrane protein OmpA, despite low sequence homology between the two enzymes. The findings from in vivo XL-MS suggest that the interacting surfaces between both β-lactamase enzymes and OmpA are conserved during molecular evolution, and the OmpA C-terminus domain serves an important function of anchoring different types of β-lactamase enzymes in the periplasmic space.

Insights into the Periplasmic Proteins of Acinetobacter baumannii AB5075 and the Impact of Imipenem Exposure: A Proteomic Approach.

Carbapenem-resistant Acinetobacter baumannii strains cause life-threatening infections due to the lack of therapeutic options. Although the main mechanisms underlying antibiotic-resistance have been extensively studied, the general response to maintain bacterial viability under antibiotic exposure deserves to be fully investigated. Since the periplasmic space contains several proteins with crucial cellular functions, besides carbapenemases, we decided to study the periplasmic proteome of the multidrug-resistant (MDR) A. baumannii AB5075 strain, grown in the absence and presence of imipenem (IMP). Through the proteomic approach, 65 unique periplasmic proteins common in both growth conditions were identified: eight proteins involved in protein fate, response to oxidative stress, energy metabolism, antibiotic-resistance, were differentially expressed. Among them, ABUW_1746 and ABUW_2363 gene products presented the tetratricopeptide repeat motif, mediating protein-protein interactions. The expression switch of these proteins might determine specific protein interactions to better adapt to changing environmental conditions. ABUW_2868, encoding a heat shock protein likely involved in protection against oxidative stress, was upregulated in IMP-exposed bacteria. Accordingly, the addition of periplasmic proteins from A. baumannii cultured with IMP increased bacterial viability in an antioxidant activity assay. Overall, this study provides the first insights about the composition of the periplasmic proteins of a MDR A. baumannii strain, its biological response to IMP and suggests possible new targets to develop alternative antibiotic drugs.

The structure of PilA from Acinetobacter baumannii AB5075 suggests a mechanism for functional specialization in Acinetobacter type IV pili

Type IV pili (T4P) are bacterial appendages composed of protein subunits, called pilins, noncovalently assembled into helical fibers. T4P are essential, in many bacterial species, for processes as diverse as twitching motility, natural competence, biofilm or microcolony formation, and host cell adhesion. The genes encoding type IV pili are found universally in the Gram-negative, aerobic, nonflagellated, and pathogenic coccobacillus Acinetobacter baumannii, but there is considerable variation in PilA, the major protein subunit, both in amino acid sequence and in glycosylation patterns. Here we report the X-ray crystal structure of PilA from AB5075, a recently characterized, highly virulent isolate, at 1.9 Å resolution and compare it to homologues from A. baumannii strains ACICU and BIDMC57, which are C-terminally glycosylated. These structural comparisons revealed that PilAAB5075 exhibits a distinctly electronegative surface chemistry. To understand the functional consequences of this change in surface electrostatics, we complemented a ΔpilA knockout strain with divergent pilA genes from ACICU, BIDMC57, and AB5075. The resulting transgenic strains showed differential twitching motility and biofilm formation while maintaining the ability to adhere to epithelial cells. PilAAB5075 and PilAACICU, although structurally similar, promote different characteristics, favoring twitching motility and biofilm formation, respectively. These results support a model in which differences in pilus electrostatics affect the equilibrium of microcolony formation, which in turn alters the balance between motility and biofilm formation in Acinetobacter.

(+)-Catechin potentiates the oxidative response of Acinetobacter baumannii to quinolone-based antibiotics

(+)-Catechin is a versatile compound with its pharmacophore (catechol and resorcinol) responsible for prooxidant and antibacterial activities. In this study, we present that demonstrating the synergistic interaction between (+)-catechin and quinolone-based antibiotics, ciprofloxacin and gemifloxacin is related to reactive oxygen species generation. The minimum inhibitory concentration of (+)-catechin against Acinetobacter baumannii AB5075 were considerably lowered for ΔsodB and ΔkatG mutants. Checkerboard assay shows synergistic interactions between (+)-catechin and quinolones. (+)-Catechin amplified quinolones-induced redox imbalance by increasing superoxide ion generation, NAD+/NADH ratio and ADP/ATP ratio. Conversely, the level of reduced glutathione was significantly lowered. We conclude that (+)-catechin potentiates quinolone-based antibiotics-induced oxidative stress in A. baumannii by increasing ROS generation, energy metabolism and electron transport chain activity with a concomitant decrease in glutathione.

Impact of zinc uptake regulator Zur on the susceptibility and oxidative stress response of Acinetobacter baumannii to antibiotics

Zinc is a highly coveted redox-inactive micronutrient required for the growth and virulence of Acinetobacter baumannii. In this study, the role of the zinc uptake regulator Zur in the susceptibility and oxidative stress response of A. baumannii to antibiotics was evaluated. Inactivation of zur increased the susceptibility of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, activities of superoxide dismutase and catalase decreased significantly in the Δzur mutant compared with the parental strain. Colistin, gentamicin, rifampicin and tigecycline raised the superoxide anion radical (·O2-) and hydrogen peroxide (H2O2) contents of the Δzur mutant compared with the parental strain. In addition, the antibiotics lowered glutathione and concomitantly raised glutathione disulphide levels in the Δzur mutant. All of the antibiotics, except tigecycline, significantly raised the NAD+/NADH and ADP/ATP ratios in A. baumannii. We conclude that decreased capability of the Δzur mutant to detoxify reactive oxygen species increased its susceptibility to antibiotics.

Ferulic acid potentiates the antibacterial activity of quinolone-based antibiotics against Acinetobacter baumannii

Ferulic acid is a cinnamic derivative of phenolic acid and its pharmacophore (catechol) is responsible for antioxidant, prooxidant and antibacterial activities. In this study, we evaluated the influence of ferulic acid on the antibacterial activity of quinolone-based antibiotics against Acinetobacter baumannii. The minimum inhibitory concentration of ferulic acid against Acinetobacter baumannii AB5075 were considerably lowered for ΔsodB and ΔkatG mutants. Checkerboard assay shows synergistic interactions between ferulic acid and quinolones. In a murine sepsis model, ferulic acid potentiated the antibacterial activities of quinolones. Ferulic acid amplified quinolones-induced redox imbalance by increasing superoxide ion generation, NAD+/NADH ratio and ADP/ATP ratio. Conversely, the level of reduced glutathione was significantly lowered. We conclude that ferulic acid potentiates the antibacterial activity of quinolone-based antibiotics against A. baumannii by increasing ROS generation, energy metabolism and electron transport chain activity with a concomitant decrease in glutathione.

Contributions of RecA and RecBCD DNA repair pathways to the oxidative stress response and sensitivity of Acinetobacter baumannii to antibiotics

ObjectivesRecA and RecBCD are responsible for the repair of oxidative DNA damage in bacteria, including Acinetobacter baumannii (A. baumannii). This study evaluated the contribution of recA, recB, recC and recD to the sensitivity and oxidative response of A. baumannii to antibiotics. ResultsInactivation of recA, recB, recC and recD significantly increased the susceptibility of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, superoxide anion radicals (•O2−) and hydrogen peroxide (H2O2) accumulated in colistin, gentamicin, rifampicin or tigecycline-treated ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants compared with the parental strain. Concomitantly, a more pronounced increase in fragmented DNA was observed in the mutants compared with the parental strain upon antibiotic treatment. Chelation of ferrous ion (Fe2+) with dipyridyl lowered the susceptibility of ΔrecA, ΔrecB, ΔrecC and ΔrecD strains of A. baumannii to colistin, gentamicin and rifampicin, but not tigecycline, to a level comparable with the parental strain. Antibiotic-mediated accumulation of reactive oxygen species depleted glutathione, with a more profound response in the mutants compared with the parental strain. The antibiotics, except tigecycline, raised the oxidized nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide and adenosine diphosphate/adenosine triphosphate ratio of ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants compared with the parental strain. ConclusionReduced capability of ΔrecA, ΔrecB, ΔrecC and ΔrecD mutants to repair DNA raised the susceptibility of A. baumannii to colistin, gentamicin, rifampicin and tigecycline. The available data further support the notion that oxidative stress contributes to antibiotic-mediated bacterial killing.

Contributions of ferric uptake regulator Fur to the sensitivity and oxidative response of Acinetobacter baumannii to antibiotics

Ferric uptake regulator (Fur) is important in the regulation of bacterial iron metabolism and uptake of Fe from the environment. We evaluated the contribution of fur to the sensitivity and oxidative response of A. baumannii to antibiotics. Deletion of fur increased the sensitivity of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, activities of superoxide dismutase and catalase in Δfur mutant decreased significantly compared to the parental strain. Conversely, •O2− and H2O2 accumulate in colistin, gentamicin, rifampicin or tigecycline-treated Δfur mutant compared to the parental strain. Ferrous ion (Fe2+) content of Δfur mutant increased compared to the parental strain. Fe chelator 2,2′-bipyridyl lowered the sensitivity of A. baumannii to the antibiotics. The antibiotics, except tigecycline, raised the NAD+/NADH and ADP/ATP ratio of Δfur mutant compared to the WT. Glutathione content of Δfur mutant was significantly depleted compared to parental strain following exposure to the antibiotics. We conclude that decreased capability of Δfur mutant to detoxify reactive oxygen species raised its susceptibility to antibiotics through Fenton chemistry.

Phenolic acids potentiate colistin-mediated killing of Acinetobacter baumannii by inducing redox imbalance

Phenolic acids with catechol groups are good prooxidants because of their low redox potential. In this study, we provided data showing that phenolic acids, caffeic acid, gallic acid and protocatechuic acid, enhanced colistin-mediated bacterial death by inducing redox imbalance. The minimum inhibitory concentrations of these phenolic acids against Acinetobacter baumannii AB5075 were considerably lowered for ΔsodB and ΔkatG mutants. Checkerboard assay shows synergistic interactions between colistin and phenolic acids. The phenolic acids exacerbated colistin-induced oxidative stress in A. baumannii AB5075 through increased superoxide anion generation, NAD + /NADH and ADP/ATP ratio. In parallel, the level of reduced glutathione was significantly lowered. We conclude that phenolic acids potentiate colistin-induced oxidative stress in A. baumannii AB5075 by increasing ROS generation, energy metabolism and electron transport chain activity with a concomitant decrease in glutathione.

Structure elucidation of the capsular polysaccharide of Acinetobacter baumannii AB5075 having the KL25 capsule biosynthesis locus

Capsular polysaccharide was isolated by the phenol–water extraction of Acinetobacter baumannii AB5075 and studied by 1D and 2D 1H and 13C NMR spectroscopy. The following structure of the linear trisaccharide repeating unit was established:→3)-β-d-ManpNAcA-(1→4)-β-d-ManpNAcA-(1→3)-α-d-QuipNAc4NR-(1→where R indicates (S)-3-hydroxybutanoyl or acetyl in the ratio∼2.5:1. The genes in the polysaccharide biosynthesis locus designated KL25 are appropriate to the established CPS structure.