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Miltefosine Reduces the Cytolytic Activity and Virulence of Acinetobacter baumannii. Antimicrob Agents Chemother 2018; 63:AAC.01409-18. [PMID: 30373804 DOI: 10.1128/aac.01409-18] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 10/23/2018] [Indexed: 12/31/2022] Open
Abstract
Stagnation in antimicrobial development has led to a serious threat to public health because some Acinetobacter baumannii infections have become untreatable. New therapeutics with alternative mechanisms of action to combat A. baumannii are therefore necessary to treat these infections. To this end, the virulence of A. baumannii isolates with various antimicrobial susceptibilities was assessed when the isolates were treated with miltefosine, a phospholipase C inhibitor. Phospholipase C activity is a contributor to A. baumannii virulence associated with hemolysis, cytolysis of A549 human alveolar epithelial cells, and increased mortality in the Galleria mellonella experimental infection model. While the effects on bacterial growth were variable among strains, miltefosine treatment significantly reduced both the hemolytic and cytolytic activity of all treated A. baumannii strains. Additionally, scanning electron microscopy of polarized A549 cells infected with bacteria of the A. baumannii ATCC 19606T strain or the AB5075 multidrug-resistant isolate showed a decrease in A549 cell damage with a concomitant increase in the presence of A549 surfactant upon administration of miltefosine. The therapeutic ability of miltefosine was further supported by the results of G. mellonella infections, wherein miltefosine treatment of animals infected with ATCC 19606T significantly decreased mortality. These data demonstrate that inhibition of phospholipase C activity results in the overall reduction of A. baumannii virulence in both in vitro and in vivo models, making miltefosine a viable option for the treatment of A. baumannii infections, particularly those caused by multidrug-resistant isolates.
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Fiester SE, Arivett BA, Schmidt RE, Beckett AC, Ticak T, Carrier MV, Ghosh R, Ohneck EJ, Metz ML, Sellin Jeffries MK, Actis LA. Iron-Regulated Phospholipase C Activity Contributes to the Cytolytic Activity and Virulence of Acinetobacter baumannii. PLoS One 2016; 11:e0167068. [PMID: 27875572 PMCID: PMC5119829 DOI: 10.1371/journal.pone.0167068] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 11/08/2016] [Indexed: 12/13/2022] Open
Abstract
Acinetobacter baumannii is an opportunistic Gram-negative pathogen that causes a wide range of infections including pneumonia, septicemia, necrotizing fasciitis and severe wound and urinary tract infections. Analysis of A. baumannii representative strains grown in Chelex 100-treated medium for hemolytic activity demonstrated that this pathogen is increasingly hemolytic to sheep, human and horse erythrocytes, which interestingly contain increasing amounts of phosphatidylcholine in their membranes. Bioinformatic, genetic and functional analyses of 19 A. baumannii isolates showed that the genomes of each strain contained two phosphatidylcholine-specific phospholipase C (PC-PLC) genes, which were named plc1 and plc2. Accordingly, all of these strains were significantly hemolytic to horse erythrocytes and their culture supernatants tested positive for PC-PLC activity. Further analyses showed that the transcriptional expression of plc1 and plc2 and the production of phospholipase and thus hemolytic activity increased when bacteria were cultured under iron-chelation as compared to iron-rich conditions. Testing of the A. baumannii ATCC 19606Tplc1::aph-FRT and plc2::aph isogenic insertion derivatives showed that these mutants had a significantly reduced PC-PLC activity as compared to the parental strain, while testing of plc1::ermAM/plc2::aph demonstrated that this double PC-PLC isogenic mutant expressed significantly reduced cytolytic and hemolytic activity. Interestingly, only plc1 was shown to contribute significantly to A. baumannii virulence using the Galleria mellonella infection model. Taken together, our data demonstrate that both PLC1 and PLC2, which have diverged from a common ancestor, play a concerted role in hemolytic and cytolytic activities; although PLC1 seems to play a more critical role in the virulence of A. baumannii when tested in an invertebrate model. These activities would provide access to intracellular iron stores this pathogen could use during growth in the infected host.
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Affiliation(s)
- Steven E. Fiester
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Brock A. Arivett
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Robert E. Schmidt
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Amber C. Beckett
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Tomislav Ticak
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Mary V. Carrier
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Rajarshi Ghosh
- Biology Department, Middle Tennessee State University, Murfreesboro, Tennessee, United States of America
| | - Emily J. Ohneck
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | - Maeva L. Metz
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
| | | | - Luis A. Actis
- Department of Microbiology, Miami University, Oxford, Ohio, United States of America
- * E-mail:
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Luo G, Spellberg B, Gebremariam T, Bolaris M, Lee H, Fu Y, French SW, Ibrahim AS. Diabetic murine models for Acinetobacter baumannii infection. J Antimicrob Chemother 2012; 67:1439-45. [PMID: 22389456 DOI: 10.1093/jac/dks050] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVES Extremely drug-resistant (XDR; i.e. resistant to all antibiotics except colistin or tigecycline) Acinetobacter baumannii has emerged as one of the most common and highly antibiotic-resistant causes of infection. Diabetes is a risk factor for acquisition of and worse outcomes from A. baumannii infection. We sought to develop diabetic mouse models of A. baumannii bacteraemia and pneumonia and validate these models by comparing the efficacy of antibiotic treatment in these models with the established neutropenic mouse models. METHODS Diabetic or neutropenic mice were infected via intravenous inoculation or inhalation in an aerosol chamber with an XDR A. baumannii. Treatment with colistin started 24 h after infection and continued daily for 7 days. Survival served as the primary endpoint while tissue bacterial burden and histopathological examination served as secondary endpoints. RESULTS Lethal infection was achieved for the neutropenic and diabetic mice when infected intravenously or via inhalation. Neutropenic mice were more susceptible to infection than diabetic mice in the pneumonia model and equally susceptible in the bacteraemia model. Both models of bacteraemia were sensitive enough to detect virulence differences among different clinical strains of A. baumannii. In the pneumonia model, colistin treatment was effective in improving survival, reducing lung bacterial burden and histologically resolving the infection compared with placebo only in diabetic mice. CONCLUSIONS We developed novel models of A. baumannii bacteraemia and pneumonia in diabetic mice. These models can be used to study mechanisms of infection, develop immunotherapeutic strategies and evaluate drug efficacies against highly lethal A. baumannii infections.
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Affiliation(s)
- Guanpingsheng Luo
- Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA 90502, USA
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