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Ji F, Tian G, Shang D, Jiang F. Antimicrobial peptide 2K4L disrupts the membrane of multidrug-resistant Acinetobacter baumannii and protects mice against sepsis. Front Microbiol 2023; 14:1258469. [PMID: 37942076 PMCID: PMC10628664 DOI: 10.3389/fmicb.2023.1258469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 10/09/2023] [Indexed: 11/10/2023] Open
Abstract
Antimicrobial peptides represent a promising therapeutic alternative for the treatment of antibiotic-resistant bacterial infections. 2K4L is a rationally-designed analog of a short peptide temporin-1CEc, a natural peptide isolated and purified from the skin secretions of the Chinese brown frog Rana chensinensis by substituting amino acid residues. 2K4L adopt an α-helical confirm in a membrane-mimetic environment and displayed an improved and broad-spectrum antibacterial activity against sensitive and multidrug-resistant Gram-negative and Gram-positive bacterial strains. Here, the action mechanism of 2K4L on multidrug resistant Acinetobacter baumannii (MRAB) and protection on MRAB-infected mice was investigated. The results demonstrated high bactericidal activity of 2K4L against both a multidrug resistant A. baumannii 0227 strain (MRAB 0227) and a sensitive A. baumannii strain (AB 22934), indicating a potential therapeutic advantage of this peptide. Strong positively-charged residues significantly promoted the electrostatic interaction on 2K4L with lipopolysaccharides (LPS) of the bacterial outer membrane. High hydrophobicity and an α-helical confirm endowed 2K4L remarkably increase the permeability of A. baumannii cytoplasmic membrane by depolarization of membrane potential and disruption of membrane integration, as well as leakage of fluorescein from the liposomes. Additionally, 2K4L at low concentrations inhibited biofilm formation and degraded mature 1-day-old MRAB 0227 biofilms by reducing the expression of biofilm-related genes. In an invasive A. baumannii infection model, 2K4L enhanced the survival of sepsis mice and decreased the production of the proinflammatory cytokines downregulating the phosphorylation level of signaling protein in MAPK and NF-κB signaling pathways, indicating that 2K4L represents a novel therapeutic antibiotic candidate against invasive multidrug-resistant bacterial strain infections.
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Affiliation(s)
- Fangyu Ji
- School of Life Science, Liaoning Normal University, Dalian, China
| | - Guoxu Tian
- School of Life Science, Liaoning Normal University, Dalian, China
| | - Dejing Shang
- School of Life Science, Liaoning Normal University, Dalian, China
- Liaoning Provincial Key Laboratory of Biotechnology and Drug Discovery, Liaoning Normal University, Dalian, China
| | - Fengquan Jiang
- Department of Clinical Laboratory, The First Affiliated Hospital of Dalian Medical University, Dalian, China
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Vasconcellos L, Silva SV, da Costa LV, de Miranda RVDSL, Dos Reis CMF, Braga LMPDS, Silva C, Conceição G, Mattoso J, Silva IB, Forsythe SJ, Midlej V, Boas MHSV, Brandão MLL. Phenotypical and molecular characterization of Acinetobacter spp. isolated from a pharmaceutical facility. Lett Appl Microbiol 2023; 76:ovad101. [PMID: 37660241 DOI: 10.1093/lambio/ovad101] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 08/14/2023] [Accepted: 08/31/2023] [Indexed: 09/04/2023]
Abstract
Characterizing microorganisms according to different criteria is useful when investigating sources of microbiological contamination in the pharmaceutical industry. The aim of this study was to characterize 38 Acinetobacter baumannii complex strains isolated from a biopharmaceutical industry by 16S rRNA sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS), multilocus sequence typing (MLST), antimicrobial susceptibility profile, biofilm formation, and sensibility to disinfectants. Thirty-three (86.9%) strains were identified by 16S rRNA gene sequencing as A. seifertii/pitti/nosocomialis/lactucae, four (10.5%) as A. baumannii, and one (2.6%) as A. vivianii/courvalini. MALDI-TOF/MS did not identify one strain, and incorrectly identified 30/37 (81.1%) strains as A. baumannii. Strains were assigned to 12 different STs, of which nine were newly defined in this study (STs 2091-2099). Twenty-six (68.4%) strains showed resistance to amikacin and gentamicin. Thirty-three (86.8%) strains were classified as moderately or strongly adherent on polystyrene. Alcohol 70%/15 min and quaternary ammonium 0.08%/20 min were not able to eliminate the biofilm formed, but sodium hypochlorite 0.1%/15 min was efficient. In conclusion, improved methods are needed to improve the identification of Acinetobacter strains in pharmaceutical industries. This organism is of particular concern as it forms recalcitrant biofilms, leading to persistence in the manufacturing environment and increased risk of product contamination.
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Affiliation(s)
- Luiza Vasconcellos
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
- Laboratory of Microbiology of Food and Sanitizes, INCQS/Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Samara Verly Silva
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Luciana Veloso da Costa
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Rebeca Vitoria da Silva Lage de Miranda
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
- Laboratory of Microbiology of Food and Sanitizes, INCQS/Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | | | | | - Claudiane Silva
- Laboratory of Cellular Ultrastructure, IOC/Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Greice Conceição
- Department of Quality Control, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Josiane Mattoso
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | - Igor Barbosa Silva
- Microbiological Control Laboratory, Bio-Manguinhos, Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
| | | | - Victor Midlej
- Laboratory of Cellular Ultrastructure, IOC/Fiocruz, Rio de Janeiro, CEP:21040-360, Brazil
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Cavallo I, Oliva A, Pages R, Sivori F, Truglio M, Fabrizio G, Pasqua M, Pimpinelli F, Di Domenico EG. Acinetobacter baumannii in the critically ill: complex infections get complicated. Front Microbiol 2023; 14:1196774. [PMID: 37425994 PMCID: PMC10325864 DOI: 10.3389/fmicb.2023.1196774] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Accepted: 06/05/2023] [Indexed: 07/11/2023] Open
Abstract
Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.
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Affiliation(s)
- Ilaria Cavallo
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Alessandra Oliva
- Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy
| | - Rebecca Pages
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Francesca Sivori
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Mauro Truglio
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Giorgia Fabrizio
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Martina Pasqua
- Department of Biology and Biotechnology "C. Darwin" Sapienza University of Rome, Rome, Italy
| | - Fulvia Pimpinelli
- Microbiology and Virology, San Gallicano Dermatological Institute, IRCCS, Rome, Italy
| | - Enea Gino Di Domenico
- Department of Biology and Biotechnology "C. Darwin" Sapienza University of Rome, Rome, Italy
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Bianchini Fulindi R, Domingues Rodrigues J, Lemos Barbosa TW, Goncalves Garcia AD, de Almeida La Porta F, Pratavieira S, Chiavacci LA, Pessoa Araújo Junior J, da Costa PI, Martinez LR. Zinc-Based Nanoparticles Reduce Bacterial Biofilm Formation. Microbiol Spectr 2023; 11:e0483122. [PMID: 36853055 PMCID: PMC10101090 DOI: 10.1128/spectrum.04831-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 02/01/2023] [Indexed: 03/01/2023] Open
Abstract
Biofilm formation is important for microbial survival in hostile environments and a phenotype that provides microorganisms with antimicrobial resistance. Zinc oxide (ZnO) and Zinc sulfide (ZnS) nanoparticles (NPs) present potential antimicrobial properties for biomedical and food industry applications. Here, we aimed to analyze, for the first time, the bactericidal and antibiofilm activity of ZnS NPs against Staphylococcus aureus, Klebsiella oxytoca, and Pseudomonas aeruginosa, all medically important bacteria in developed countries. We compared ZnS NPs antimicrobial activity to ZnO NPs, which have been extensively studied. Using the colorimetric XTT reduction assay to observe the metabolic activity of bacterial cells and the crystal violet assay to measure biofilm mass, we demonstrated that ZnS and ZnO had similar efficacy in killing planktonic bacterial cells and reducing biofilm formation, with S. aureus being more susceptible to both therapeutics than K. oxytoca and P. aeruginosa. Crystal violet staining and confocal microscopy validated that Zn NPs inhibit biofilm formation and cause architectural damage. Our findings provide proof of principle that ZnS NPs have antibiofilm activity, and can be potentially used in medical and food industry applications, such as treatment of wound infections or package coating for food preservation. IMPORTANCE Zinc (Zn)-based nanoparticles (NPs) can be potentially used in medical and food preservation applications. As proof of principle, we investigated the bactericidal and antibiofilm activity of zinc oxide (ZnO) and zinc sulfide (ZnS) NPs against medically important bacteria. Zn-based NPs were similarly effective in killing planktonic and biofilm-associated Staphylococcus aureus, Klebsiella oxytoca, and Pseudomonas aeruginosa cells. However, S. aureus was more susceptible to these investigational therapeutics. Although further studies are warranted, our findings suggest the possibility of future use of Zn-based NPs in the treatment of skin infections or preservation of food.
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Affiliation(s)
- Rafael Bianchini Fulindi
- Departments of Clinical Analysis, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | | | - Thulio Wliandon Lemos Barbosa
- Departments of Drugs and Medicines, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | | | | | - Sebastião Pratavieira
- São Carlos Physics Department, University of São Paulo, São Carlos, São Paulo, Brazil
| | - Leila Aparecida Chiavacci
- Departments of Drugs and Medicines, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | | | - Paulo Inácio da Costa
- Departments of Clinical Analysis, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | - Luis R. Martinez
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, Florida, USA
- Emerging Pathogens Institute, University of Florida, Gainesville, Florida, USA
- Center for Immunology and Transplantation, University of Florida, Gainesville, Florida, USA
- Center for Translational Research in Neurodegenerative Disease, University of Florida, Gainesville, Florida, USA
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Korzeniowski P, Śliwka P, Kuczkowski M, Mišić D, Milcarz A, Kuźmińska-Bajor M. Bacteriophage Cocktail Can Effectively Control Salmonella Biofilm in Poultry Housing. Front Microbiol 2022; 13:901770. [PMID: 35847069 PMCID: PMC9277115 DOI: 10.3389/fmicb.2022.901770] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 06/02/2022] [Indexed: 11/13/2022] Open
Abstract
Salmonella enterica serovar Enteritidis (S. Enteritidis) is the major contaminant of poultry products, and its ability to form biofilms on produced food and poultry farm processing surfaces contributes to Salmonella transmission to humans. Bacteriophages have come under increasing interest for anti-Salmonella biofilm control. In this study, we used the three previously sequenced and described phages UPWr_S1, UPWr_S3, and UPWr_S4 and a phage cocktail, UPWr_S134, containing these three phages to degrade biofilms formed by two S. Enteritidis strains, 327 lux and ATCC 13076, in vitro. It was found that treatment with bacteriophages significantly reduced biofilm on a 96-well microplate (32–69%) and a stainless steel surface (52–98%) formed by S. Enteritidis 327 lux. The reduction of biofilm formed by S. Enteritidis ATCC 13076 in the 96-well microplate and on a stainless steel surface for bacteriophage treatment was in the range of 73–87% and 60–97%, respectively. Under laboratory conditions, an experimental model utilizing poultry drinkers artificially contaminated with S. Enteritidis 327 lux and treated with UPWr_S134 phage cocktail was applied. In in vitro trials, the phage cocktail significantly decreased the number of Salmonella on the surface of poultry drinkers. Moreover, the phage cocktail completely eradicated Salmonella from the abundant bacterial load on poultry drinkers in an experimentally infected chickens. Therefore, the UPWr_S134 phage cocktail is a promising candidate for Salmonella biocontrol at the farm level.
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Affiliation(s)
- Paweł Korzeniowski
- Department of Biotechnology and Food Microbiology, Faculty of Biotechnology and Food Sciences, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Paulina Śliwka
- Department of Biotechnology and Food Microbiology, Faculty of Biotechnology and Food Sciences, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Maciej Kuczkowski
- Department of Epizootiology and Clinic of Birds and Exotic Animals, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Dušan Mišić
- Department of Functional Food Products Development, Faculty of Biotechnology and Food Sciences, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Agata Milcarz
- Department of Biotechnology and Food Microbiology, Faculty of Biotechnology and Food Sciences, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
| | - Marta Kuźmińska-Bajor
- Department of Biotechnology and Food Microbiology, Faculty of Biotechnology and Food Sciences, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
- *Correspondence: Marta Kuźmińska-Bajor
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CsrA-Controlled Proteins Reveal New Dimensions of Acinetobacter baumannii Desiccation Tolerance. J Bacteriol 2022; 204:e0047921. [PMID: 35285725 DOI: 10.1128/jb.00479-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Hospital environments are excellent reservoirs for the opportunistic pathogen Acinetobacter baumannii in part because it is exceptionally tolerant to desiccation. We found that relative to other A. baumannii strains, the virulent strain AB5075 was strikingly desiccation resistant at 2% relative humidity (RH), suggesting that it is a good model for studies of the functional basis of this trait. Consistent with results from other A. baumannii strains at 40% RH, we found the global posttranscriptional regulator CsrA to be critically important for desiccation tolerance of AB5075 at 2% RH. Proteomics experiments identified proteins that were differentially present in wild-type and csrA mutant cells. Subsequent analysis of mutants in genes encoding some of these proteins revealed six genes that were required for wild-type levels of desiccation tolerance. These include genes for catalase, a universal stress protein, a hypothetical protein, and a biofilm-associated protein. Two genes of unknown function had very strong desiccation phenotypes, with one of the two genes predicting an intrinsically disordered protein (IDP) that binds to DNA. Intrinsically disordered proteins are widespread in eukaryotes but less so in prokaryotes. Our results suggest there are new mechanisms underlying desiccation tolerance in bacteria and identify several key functions involved. IMPORTANCE Acinetobacter baumannii is found in terrestrial environments but can cause nosocomial infections in very sick patients. A factor that contributes to the prevalence of A. baumannii in hospital settings is that it is intrinsically resistant to dry conditions. Here, we established the virulent strain A. baumannii AB5075 as a model for studies of desiccation tolerance at very low relative humidity. Our results show that this trait depends on two proteins of unknown function, one of which is predicted to be an intrinsically disordered protein. This category of protein is critical for the small animals named tardigrades to survive desiccation. Our results suggest that A. baumannii may have novel strategies to survive desiccation that have not previously been seen in bacteria.
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Robin B, Nicol M, Le H, Tahrioui A, Schaumann A, Vuillemenot JB, Vergoz D, Lesouhaitier O, Jouenne T, Hardouin J, Potron A, Perrot V, Dé E. MacAB-TolC Contributes to the Development of Acinetobacter baumannii Biofilm at the Solid–Liquid Interface. Front Microbiol 2022; 12:785161. [PMID: 35095797 PMCID: PMC8792954 DOI: 10.3389/fmicb.2021.785161] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 11/22/2021] [Indexed: 12/14/2022] Open
Abstract
Acinetobacter baumannii has emerged as one of the most problematic bacterial pathogens responsible for hospital-acquired and community infections worldwide. Besides its high capacity to acquire antibiotic resistance mechanisms, it also presents high adhesion abilities on inert and living surfaces leading to biofilm development. This lifestyle confers additional protection against various treatments and allows it to persist for long periods in various hospital niches. Due to their remarkable antimicrobial tolerance, A. baumannii biofilms are difficult to control and ultimately eradicate. Further insights into the mechanism of biofilm development will help to overcome this challenge and to develop novel antibiofilm strategies. To unravel critical determinants of this sessile lifestyle, the proteomic profiles of two A. baumannii strains (ATTC17978 and SDF) grown in planktonic stationary phase or in mature solid–liquid (S-L) biofilm were compared using a semiquantitative proteomic study. Of interest, among the 69 common proteins determinants accumulated in the two strains at the S-L interface, we sorted out the MacAB-TolC system. This tripartite efflux pump played a role in A. baumannii biofilm formation as demonstrated by using ΔmacAB-tolC deletion mutant. Complementary approaches allowed us to get an overview of the impact of macAB-tolC deletion in A. baumannii physiology. Indeed, this efflux pump appeared to be involved in the envelope stress response occurring in mature biofilm. It contributes to maintain wild type (WT) membrane rigidity and provides tolerance to high osmolarity conditions. In addition, this system is probably involved in the maintenance of iron and sulfur homeostasis. MacAB-TolC might help this pathogen face and adapt to deleterious conditions occurring in mature biofilms. Increasing our knowledge of A. baumannii biofilm formation will undoubtedly help us develop new therapeutic strategies to tackle this emerging threat to human health.
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Affiliation(s)
- Brandon Robin
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
| | - Marion Nicol
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
| | - Hung Le
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
| | - Ali Tahrioui
- Normandie Univ, UNIROUEN, LMSM EA4312, Evreux, France
| | - Annick Schaumann
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
- PISSARO Proteomic Facility, IRIB, Mont-Saint-Aignan, France
| | | | - Delphine Vergoz
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
| | | | - Thierry Jouenne
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
- PISSARO Proteomic Facility, IRIB, Mont-Saint-Aignan, France
| | - Julie Hardouin
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
- PISSARO Proteomic Facility, IRIB, Mont-Saint-Aignan, France
| | - Anaïs Potron
- UMR 6249 Chrono-Environnement, CNRS-Université de Bourgogne/Franche-Comté, Besançon, France
| | - Valérie Perrot
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
- *Correspondence: Valérie Perrot,
| | - Emmanuelle Dé
- Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Polymers, Biopolymers, Surfaces Laboratory, Rouen, France
- Emmanuelle Dé,
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Abstract
OBJECTIVE Environmental surfaces may serve as potential reservoirs for nosocomial pathogens and facilitate transmissions via contact depending on its tenacity. This study provides data on survival kinetics of the most important nosocomial bacteria on a panel of commonly used surfaces. Type strains of S. aureus, K. pneumoniae, P. aeruginosa, A. baumannii, S. marcescens, E. faecium, E. coli, and E. cloacae were suspended in 0.9% NaCl solution at a McFarland of 1 and got then plated via cotton swabs either on glass, polyvinyl chloride, stainless steel, or aluminum. Surfaces were stored at regular ambient temperature and humidity to simulate routine daycare conditions. Sampling was performed by contact plates for a time period of four weeks. RESULTS The longest survival was observed for A. baumannii and E. faecium on all materials (at least four weeks). S. aureus remained viable for at least one week. Gram negative species other than A. baumannii were usually inactivated in less than two days. Nosocomial transmission of the above mentioned bacteria may easily occur if no appropriate infection control measures are applied on a regular daily basis. This might be of particular importance when dealing with outbreaks of A. baumannii and E. faecium.
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Belisario JC, Lee HH, Luknauth H, Rigel NW, Martinez LR. Acinetobacter baumannii Strains Deficient in the Clp Chaperone-Protease Genes Have Reduced Virulence in a Murine Model of Pneumonia. Pathogens 2021; 10:pathogens10020204. [PMID: 33668542 PMCID: PMC7917692 DOI: 10.3390/pathogens10020204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 02/08/2021] [Accepted: 02/09/2021] [Indexed: 01/05/2023] Open
Abstract
Acinetobacter baumannii has emerged as a significant opportunistic Gram-negative pathogen and causative agent of nosocomial pneumonia especially in immunocompromised individuals in intensive care units. Recent advances to understand the contribution and function of A. baumannii virulence factors in its pathogenesis have begun to elucidate how this bacterium interacts with immune cells and its interesting mechanisms for multi-antibiotic resistance. Taking advantage of the availability of the A. baumannii AB5075 transposon mutant library, we investigated the impact of the A. baumannii Clp genes, which encode for a chaperone-protease responsible for the degradation of misfolded proteins, on bacterial virulence in a model of pneumonia using C57BL/6 mice and survival within J774.16 macrophage-like cells. Clp-protease A. baumannii mutants exhibit decreased virulence in rodents, high phagocytic cell-mediated killing and reduced biofilm formation. Capsular staining showed evidence of encapsulation in A. baumannii AB5075 and Clp-mutant strains. Surprisingly, clpA and clpS mutants displayed irregular cell morphology, which may be important in the biofilm structural deficiencies observed in these strains. Interestingly, clpA showed apical-like growth, proliferation normally observed in filamentous fungi. These findings provide new information regarding A. baumannii pathogenesis and may be important for the development of therapies intended at reducing morbidity and mortality associated with this remarkable pathogen.
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Affiliation(s)
- J Christian Belisario
- Department of Physical Medicine and Rehabilitation, University of Pennsylvania, Philadelphia, PA 19146, USA;
- Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA;
| | - Hiu Ham Lee
- Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA;
| | - Harshani Luknauth
- Department of Biology, Hofstra University, Hempstead, NY 11549, USA; (H.L.); (N.W.R.)
| | - Nathan W. Rigel
- Department of Biology, Hofstra University, Hempstead, NY 11549, USA; (H.L.); (N.W.R.)
| | - Luis R. Martinez
- Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA;
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL 32610, USA
- Correspondence:
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Relucenti M, Familiari G, Donfrancesco O, Taurino M, Li X, Chen R, Artini M, Papa R, Selan L. Microscopy Methods for Biofilm Imaging: Focus on SEM and VP-SEM Pros and Cons. BIOLOGY 2021; 10:biology10010051. [PMID: 33445707 PMCID: PMC7828176 DOI: 10.3390/biology10010051] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 12/30/2020] [Accepted: 01/07/2021] [Indexed: 12/11/2022]
Abstract
Simple Summary Bacterial biofilms cause infections that are often resistant to antibiotic treatments. Research about the formation and elimination of biofilms cannot be undertaken without detailed imaging techniques. In this review, traditional and cutting-edge microscopy methods to study biofilm structure, ultrastructure, and 3-D architecture, with particular emphasis on conventional scanning electron microscopy and variable pressure scanning electron microscopy, are addressed, with the respective advantages and disadvantages. When ultrastructural characterization of biofilm matrix and its embedded bacterial cells is needed, as in studies on the effects of drug treatments on biofilm, scanning electron microscopy with customized protocols such as the osmium tetroxide (OsO4), ruthenium red (RR), tannic acid (TA), and ionic liquid (IL) must be preferred over other methods for the following: unparalleled image quality, magnification and resolution, minimal sample loss, and actual sample structure preservation. The first step to make a morphological assessment of the effect of the various pharmacological treatments on clinical biofilms is the production of images that faithfully reflect the structure of the sample. The extraction of quantitative parameters from images, possible using specific software, will allow for the scanning electron microscopy morphological evaluation to no longer be considered as an accessory technique, but a quantitative method to all effects. Abstract Several imaging methodologies have been used in biofilm studies, contributing to deepening the knowledge on their structure. This review illustrates the most widely used microscopy techniques in biofilm investigations, focusing on traditional and innovative scanning electron microscopy techniques such as scanning electron microscopy (SEM), variable pressure SEM (VP-SEM), environmental SEM (ESEM), and the more recent ambiental SEM (ASEM), ending with the cutting edge Cryo-SEM and focused ion beam SEM (FIB SEM), highlighting the pros and cons of several methods with particular emphasis on conventional SEM and VP-SEM. As each technique has its own advantages and disadvantages, the choice of the most appropriate method must be done carefully, based on the specific aim of the study. The evaluation of the drug effects on biofilm requires imaging methods that show the most detailed ultrastructural features of the biofilm. In this kind of research, the use of scanning electron microscopy with customized protocols such as osmium tetroxide (OsO4), ruthenium red (RR), tannic acid (TA) staining, and ionic liquid (IL) treatment is unrivalled for its image quality, magnification, resolution, minimal sample loss, and actual sample structure preservation. The combined use of innovative SEM protocols and 3-D image analysis software will allow for quantitative data from SEM images to be extracted; in this way, data from images of samples that have undergone different antibiofilm treatments can be compared.
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Affiliation(s)
- Michela Relucenti
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, Via Alfonso Borelli 50, 00161 Rome, Italy; (G.F.); (O.D.)
- Correspondence: ; Tel.: +39-0649918061
| | - Giuseppe Familiari
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, Via Alfonso Borelli 50, 00161 Rome, Italy; (G.F.); (O.D.)
| | - Orlando Donfrancesco
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, Via Alfonso Borelli 50, 00161 Rome, Italy; (G.F.); (O.D.)
| | - Maurizio Taurino
- Department of Clinical and Molecular Medicine, Unit of Vascular Surgery, Sant’Andrea Hospital, Sapienza University of Rome, Via di Grottarossa 1039, 00189 Rome, Italy;
| | - Xiaobo Li
- Key Laboratory of Environmental Medicine Engineering, Ministry of Education, School of Public Health, Southeast University, Nanjing 210096, China; (X.L.); (R.C.)
| | - Rui Chen
- Key Laboratory of Environmental Medicine Engineering, Ministry of Education, School of Public Health, Southeast University, Nanjing 210096, China; (X.L.); (R.C.)
| | - Marco Artini
- Department of Public Health and Infectious Diseases, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy; (M.A.); (R.P.); (L.S.)
| | - Rosanna Papa
- Department of Public Health and Infectious Diseases, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy; (M.A.); (R.P.); (L.S.)
| | - Laura Selan
- Department of Public Health and Infectious Diseases, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy; (M.A.); (R.P.); (L.S.)
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11
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Depletion of Alveolar Macrophages Increases Pulmonary Neutrophil Infiltration, Tissue Damage, and Sepsis in a Murine Model of Acinetobacter baumannii Pneumonia. Infect Immun 2020; 88:IAI.00128-20. [PMID: 32366576 DOI: 10.1128/iai.00128-20] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 04/30/2020] [Indexed: 12/14/2022] Open
Abstract
Acinetobacter baumannii has emerged as an important etiological agent of hospital-related infections, especially nosocomial pneumonia. The virulence factors of this bacterium and their interactions with the cells and molecules of the immune system just recently began to be extensively studied. Here, we investigated the impact of alveolar macrophages on A. baumannii pneumonia using a mouse model of infection and a flexible tissue culture system. We hypothesized that depletion of macrophages would enhance sepsis and severity of A. baumannii disease. We showed that macrophages are important for modulating the antibacterial function of neutrophils and play an important role in eradicating A. baumannii infection in vivo Our findings suggest that in the absence of macrophages in the lungs, A. baumannii replicates significantly, and host proinflammatory cytokines are considerably reduced. Neutrophils are abundantly recruited to pulmonary tissue, releasing high amounts of reactive oxygen species and causing extensive tissue damage. The ability of A. baumannii to form biofilms and resist oxidative stress in the respiratory tract facilitates systemic dissemination and ultimately death of infected C57BL/6 mice. These results provide novel information regarding A. baumannii pathogenesis and may be important for the development of therapies aimed at reducing morbidity and mortality associated with this emerging bacterial pathogen.
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12
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Lin MF, Lin YY, Lan CY. Characterization of biofilm production in different strains of Acinetobacter baumannii and the effects of chemical compounds on biofilm formation. PeerJ 2020; 8:e9020. [PMID: 32523805 PMCID: PMC7261477 DOI: 10.7717/peerj.9020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 03/28/2020] [Indexed: 12/23/2022] Open
Abstract
Acinetobacter baumannii, an important emerging pathogen of nosocomial infections, is known for its ability to form biofilms. Biofilm formation increases the survival rate of A. baumannii on dry surfaces and may contribute to its persistence in the hospital environment, which increases the probability of nosocomial infections and outbreaks. This study was undertaken to characterize the biofilm production of different strains of A. baumannii and the effects of chemical compounds, especially antibiotics, on biofilm formation. In this study, no statistically significant relationship was observed between the ability to form a biofilm and the antimicrobial susceptibility of the A. baumannii clinical isolates. Biofilm formation caused by A. baumannii ATCC 17978 after gene knockout of two-component regulatory system gene baeR, efflux pump genes emrA/emrB and outer membrane coding gene ompA revealed that all mutant strains had less biofilm formation than the wild-type strain, which was further supported by the images from scanning electron microscopy and confocal laser scanning microscopy. The addition of amikacin, colistin, LL-37 or tannic acid decreased the biofilm formation ability of A. baumannii. In contrast, the addition of lower subinhibitory concentration tigecycline increased the biofilm formation ability of A. baumannii. Minimum biofilm eradication concentrations of amikacin, imipenem, colistin, and tigecycline were increased obviously for both wild type and multidrug resistant clinical strain A. baumannii VGH2. In conclusion, the biofilm formation ability of A. baumannii varied in different strains, involved many genes and could be influenced by many chemical compounds.
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Affiliation(s)
- Ming-Feng Lin
- Department of Medicine, National Taiwan University Hospital Chu-Tung Branch, Hsinchu County, Taiwan
| | - Yun-You Lin
- Institute of Molecular and Cellular Biology, National Tsing Hua University, Hsinchu, Taiwan
| | - Chung-Yu Lan
- Institute of Molecular and Cellular Biology, National Tsing Hua University, Hsinchu, Taiwan.,Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan
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13
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14
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Bravo Z, Orruño M, Navascues T, Ogayar E, Ramos-Vivas J, Kaberdin VR, Arana I. Analysis of Acinetobacter baumannii survival in liquid media and on solid matrices as well as effect of disinfectants. J Hosp Infect 2019; 103:e42-e52. [PMID: 30986481 DOI: 10.1016/j.jhin.2019.04.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Accepted: 04/07/2019] [Indexed: 12/18/2022]
Abstract
BACKGROUND Acinetobacter baumannii is a cause of healthcare-associated infections and has considerable potential to survive on inanimate hospital surfaces under hostile conditions (e.g. disinfection or desiccation). AIM To learn more about its survival strategy and capacity to persist in liquid media and on surfaces mimicking hospital environments. METHODS The effect of temperature, nutrient deprivation, permanence on inanimate surfaces, and exposure to disinfectants on the survival of four A. baumannii strains (ATCC 19606T and three clinical isolates) was studied by monitoring the number of total and viable cells using fluorescent microscopy and of culturable cells by standard cultures. FINDINGS Bacterial survival was differentially affected by temperature (cells maintained at 20°C remained culturable at least within 30 days) and physical environment (desiccation favoured cell resistance to stress at 37°C). Moreover, persistence was associated with two adaptation patterns: one linked to entry into the viable but non-culturable state, whereas the other apparently followed a bust-and-boom model. During a study on the effect of disinfectant (commercial bleach and quaternary ammonium compounds), it was found that treatment with these antibacterial compounds did not eliminate A. baumannii populations and provoked the reduction of culturable populations, although a fraction of cells remained culturable. CONCLUSION The ability to persist for long periods on different surfaces, mimicking those usually found in hospitals, along with A. baumannii's capacity to survive after a disinfection process may account for the recurrent outbreaks in intensive care units.
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Affiliation(s)
- Z Bravo
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain; Instituto de Investigación Valdecilla IDIVAL, Santander, Spain
| | - M Orruño
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain; Research Centre for Experimental Marine Biology and Biotechnology (PIE-UPV/EHU), Plentzia, Spain.
| | - T Navascues
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain; Instituto de Investigación Valdecilla IDIVAL, Santander, Spain
| | - E Ogayar
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain
| | - J Ramos-Vivas
- Instituto de Investigación Valdecilla IDIVAL, Santander, Spain
| | - V R Kaberdin
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain; Research Centre for Experimental Marine Biology and Biotechnology (PIE-UPV/EHU), Plentzia, Spain; Ikerbasque, Basque Foundation for Science, Bilbao, Spain
| | - I Arana
- Department of Immunology, Microbiology and Parasitology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain; Research Centre for Experimental Marine Biology and Biotechnology (PIE-UPV/EHU), Plentzia, Spain
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15
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Flynn PB, Graham WG, Gilmore BF. Acinetobacter baumannii biofilm biomass mediates tolerance to cold plasma. Lett Appl Microbiol 2019; 68:344-349. [PMID: 30706947 PMCID: PMC6446819 DOI: 10.1111/lam.13122] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 01/22/2019] [Accepted: 01/22/2019] [Indexed: 12/22/2022]
Abstract
Acinetobacter baumannii is an intrinsically multidrug‐resistant pathogen that, when existing as a biofilm, confers increased environmental tolerance to desiccation, nutrient starvation as well as increased tolerance to antimicrobials. Outbreaks of A. baumannii infections within the clinical setting are often associated with the biofilm phenotype. This study investigates the role of biofilm biomass in A. baumannii susceptibility to exposure to a kilohertz‐driven, in‐house–designed, cold plasma jet, through the examination of cold plasma treatment efficacy in A. baumannii biofilms grown over various times for up to 72 h. For biofilms grown for 24, 48 and 72 h, D values were 19·32 ± 2·71, 29·18 ± 3·15 and 24·70 ± 3·07 s respectively. Monitoring A. baumannii biofilm biomass over these time periods revealed that the greatest biomass was observed at 48 h with the lowest biofilm biomass at 24 h growth. Enumeration of viable biofilm colony counts at each time point was comparable. Scanning electron microscopy images of plasma‐treated biofilms revealed extensive surface damage of A. baumannii cells. These results describe the role of biomass in mediating A. baumannii biofilm susceptibility to cold plasma treatment, implicating the biofilm matrix as a protective barrier to the antimicrobial effects of cold plasma. Significance and Impact of the Study Acinetobacter baumannii biofilm formation results in increased environmental and antimicrobial tolerance and resistance compared to the planktonic phenotype. Cold plasma technology is increasingly investigated as a new tool for decontamination of biofilm‐contaminated surfaces, especially those found in the clinical setting. This new technology presents a promising approach to the remediation of surfaces contaminated by biofilms. This study identifies the role played by A. baumannii biofilm biomass in mediating tolerance and susceptibility to cold plasma treatment. This work demonstrates that increased biofilm biomass reduces the efficacy of antimicrobial species generated by cold plasma, resulting in greater tolerance to plasma exposure.
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Affiliation(s)
- P B Flynn
- Biofilm Research Group, School of Pharmacy, Queen's University, Belfast, UK
| | - W G Graham
- Centre for Plasma Physics (CPP), School of Mathematics and Physics, Queens University, Belfast, UK
| | - B F Gilmore
- Biofilm Research Group, School of Pharmacy, Queen's University, Belfast, UK
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16
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Zeidler S, Müller V. Coping with low water activities and osmotic stress in Acinetobacter baumannii: significance, current status and perspectives. Environ Microbiol 2019; 21:2212-2230. [PMID: 30773801 DOI: 10.1111/1462-2920.14565] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 02/11/2019] [Accepted: 02/13/2019] [Indexed: 01/26/2023]
Abstract
Multidrug resistant (MDR) pathogens are one of the most pressing challenges of contemporary health care. Acinetobacter baumannii takes a predominant position, emphasized in 2017 by the World Health Organization. The increasing emergence of MDR strains strengthens the demand for new antimicrobials. Possible targets for such compounds might be proteins involved in resistance against low water activity environments, since A. baumannii is known for its pronounced resistance against desiccation stress. Despite the importance of desiccation resistance for persistence of this pathogen in hospitals, comparable studies and precise data on this topic are rare and the mechanisms involved are largely unknown. This review aims to give an overview of the studies performed so far and the current knowledge on genes and proteins important for desiccation survival. 'Osmotic stress' is not identical to 'desiccation stress', but the two share the response of bacteria to low water activities. Osmotic stress resistance is in general studied much better, and in recent years it turned out that accumulation of compatible solutes in A. baumannii comprises some special features such as the bifunctional enzyme MtlD synthesizing the unusual solute mannitol. Furthermore, the regulatory pathways, as understood today, will be discussed.
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Affiliation(s)
- Sabine Zeidler
- Department of Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany
| | - Volker Müller
- Department of Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany
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17
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Eze EC, Chenia HY, El Zowalaty ME. Acinetobacter baumannii biofilms: effects of physicochemical factors, virulence, antibiotic resistance determinants, gene regulation, and future antimicrobial treatments. Infect Drug Resist 2018; 11:2277-2299. [PMID: 30532562 PMCID: PMC6245380 DOI: 10.2147/idr.s169894] [Citation(s) in RCA: 123] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Acinetobacter baumannii is a leading cause of nosocomial infections due to its increased antibiotic resistance and virulence. The ability of A. baumannii to form biofilms contributes to its survival in adverse environmental conditions including hospital environments and medical devices. A. baumannii has undoubtedly propelled the interest of biomedical researchers due to its broad range of associated infections especially in hospital intensive care units. The interplay among microbial physicochemistry, alterations in the phenotype and genotypic determinants, and the impact of existing ecological niche and the chemistry of antimicrobial agents has led to enhanced biofilm formation resulting in limited access of drugs to their specific targets. Understanding the triggers to biofilm formation is a step towards limiting and containing biofilm-associated infections and development of biofilm-specific countermeasures. The present review therefore focused on explaining the impact of environmental factors, antimicrobial resistance, gene alteration and regulation, and the prevailing microbial ecology in A. baumannii biofilm formation and gives insights into prospective anti-infective treatments.
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Affiliation(s)
- Emmanuel C Eze
- Virology and Microbiology Research Group, School of Health Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa,
| | - Hafizah Y Chenia
- Discipline of Microbiology, School of Life Sciences, College of Agriculture, Engineering and Sciences, University of KwaZulu-Natal, Durban, South Africa
| | - Mohamed E El Zowalaty
- Virology and Microbiology Research Group, School of Health Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa,
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18
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Zeidler S, Müller V. The role of compatible solutes in desiccation resistance of Acinetobacter baumannii. Microbiologyopen 2018; 8:e00740. [PMID: 30277310 PMCID: PMC6528591 DOI: 10.1002/mbo3.740] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 08/30/2018] [Accepted: 08/31/2018] [Indexed: 01/03/2023] Open
Abstract
Acinetobacter baumannii is a nosocomial pathogen which can persist in the hospital environment not only due to the acquirement of multiple antibiotic resistances, but also because of its exceptional resistance against disinfectants and desiccation. A suitable desiccation assay was established in which A. baumannii ATCC 19606T survived for ca. 1 month. The growth medium slightly influenced survival after subsequent desiccation. A significant effect could be attributed to the growth phase in which bacteria were dried: In exponential phase, cells were much more desiccation sensitive. The main focus of the present study was the elucidation of the role of compatible solutes, which are known to protect many bacteria under low water activity conditions, in desiccation survival of A. baumannii. Exogenous trehalose was shown to efficiently protect A. baumannii on dry surfaces, in contrast to other compatible solutes tested such as mannitol or glycine betaine. To analyze the importance of intracellularly accumulated solutes, a double mutant lacking biosynthesis pathways for mannitol and trehalose was generated. This mutant accumulated glutamate as sole solute in the presence of high NaCl concentrations and showed severe growth defects under osmotic stress conditions. However, no effect on desiccation tolerance could be seen, neither when cells were dried in water nor in the presence of NaCl.
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Affiliation(s)
- Sabine Zeidler
- Department of Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe-University Frankfurt am Main, Frankfurt, Germany
| | - Volker Müller
- Department of Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe-University Frankfurt am Main, Frankfurt, Germany
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19
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Pandit S, Shanbhag S, Mauter M, Oren Y, Herzberg M. Influence of Electric Fields on Biofouling of Carbonaceous Electrodes. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:10022-10030. [PMID: 28741939 DOI: 10.1021/acs.est.6b06339] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Biofouling commonly occurs on carbonaceous capacitive deionization electrodes in the process of treating natural waters. Although previous work reported the effect of electric fields on bacterial mortality for a variety of medical and engineered applications, the effect of electrode surface properties and the magnitude and polarity of applied electric fields on biofilm development has not been comprehensively investigated. This paper studies the formation of a Pseudomonas aeruginosa biofilm on a Papyex graphite (PA) and a carbon aerogel (CA) in the presence and the absence of an electric field. The experiments were conducted using a two-electrode flow cell with a voltage window of ±0.9 V. The CA was less susceptible to biofilm formation compared to the PA due to its lower surface roughness, lower hydrophobicity, and significant antimicrobial properties. For both positive and negative applied potentials, we observed an inverse relationship between biofilm formation and the magnitude of the applied potential. The effect is particularly strong for the CA electrodes and may be a result of cumulative effects between material toxicity and the stress experienced by cells at high applied potentials. Under the applied potentials for both electrodes, high production of endogenous reactive oxygen species (ROS) was indicative of bacterial stress. For both electrodes, the elevated specific ROS activity was lowest for the open circuit potential condition, elevated when cathodically and anodically polarized, and highest for the ±0.9 V cases. These high applied potentials are believed to affect the redox potential across the cell membrane and disrupt redox homeostasis, thereby inhibiting bacterial growth.
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Affiliation(s)
- Soumya Pandit
- Zuckerberg Institute for Water Research, Blaustein Institutes for Desert Research, Ben Gurion University of the Negev , Midreshet Ben Gurion 84990, Israel
| | | | | | - Yoram Oren
- Zuckerberg Institute for Water Research, Blaustein Institutes for Desert Research, Ben Gurion University of the Negev , Midreshet Ben Gurion 84990, Israel
| | - Moshe Herzberg
- Zuckerberg Institute for Water Research, Blaustein Institutes for Desert Research, Ben Gurion University of the Negev , Midreshet Ben Gurion 84990, Israel
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Azeredo J, Azevedo NF, Briandet R, Cerca N, Coenye T, Costa AR, Desvaux M, Di Bonaventura G, Hébraud M, Jaglic Z, Kačániová M, Knøchel S, Lourenço A, Mergulhão F, Meyer RL, Nychas G, Simões M, Tresse O, Sternberg C. Critical review on biofilm methods. Crit Rev Microbiol 2016; 43:313-351. [PMID: 27868469 DOI: 10.1080/1040841x.2016.1208146] [Citation(s) in RCA: 536] [Impact Index Per Article: 67.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Biofilms are widespread in nature and constitute an important strategy implemented by microorganisms to survive in sometimes harsh environmental conditions. They can be beneficial or have a negative impact particularly when formed in industrial settings or on medical devices. As such, research into the formation and elimination of biofilms is important for many disciplines. Several new methodologies have been recently developed for, or adapted to, biofilm studies that have contributed to deeper knowledge on biofilm physiology, structure and composition. In this review, traditional and cutting-edge methods to study biofilm biomass, viability, structure, composition and physiology are addressed. Moreover, as there is a lack of consensus among the diversity of techniques used to grow and study biofilms. This review intends to remedy this, by giving a critical perspective, highlighting the advantages and limitations of several methods. Accordingly, this review aims at helping scientists in finding the most appropriate and up-to-date methods to study their biofilms.
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Affiliation(s)
- Joana Azeredo
- a CEB ? Centre of Biological Engineering, LIBRO, Laboratórios de Biofilmes Rosário Oliveira, University of Minho Campus de Gualtar , Braga , Portugal
| | - Nuno F Azevedo
- b LEPABE, Department of Chemical Engineering, Faculty of Engineering , University of Porto , Porto , Portugal
| | - Romain Briandet
- c Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay , Jouy-en-Josas , France
| | - Nuno Cerca
- a CEB ? Centre of Biological Engineering, LIBRO, Laboratórios de Biofilmes Rosário Oliveira, University of Minho Campus de Gualtar , Braga , Portugal
| | - Tom Coenye
- d Laboratory of Pharmaceutical Microbiology , Ghent University , Ghent , Belgium
| | - Ana Rita Costa
- a CEB ? Centre of Biological Engineering, LIBRO, Laboratórios de Biofilmes Rosário Oliveira, University of Minho Campus de Gualtar , Braga , Portugal
| | - Mickaël Desvaux
- e INRA Centre Auvergne-Rhône-Alpes , UR454 Microbiologie , Saint-Genès Champanelle , France
| | - Giovanni Di Bonaventura
- f Department of Medical, Oral, and Biotechnological Sciences, and Center of Excellence on Aging and Translational Medicine (CeSI-MeT) , "G. d'Annunzio" University of Chieti-Pescara , Chieti , Italy
| | - Michel Hébraud
- e INRA Centre Auvergne-Rhône-Alpes , UR454 Microbiologie , Saint-Genès Champanelle , France
| | - Zoran Jaglic
- g Department of Food and Feed Safety, Laboratory of Food Bacteriology , Veterinary Research Institute , Brno , Czech Republic
| | - Miroslava Kačániová
- h Department of Microbiology, Faculty of Biotechnology and Food Sciences , Slovak University of Agriculture in Nitra , Nitra , Slovakia
| | - Susanne Knøchel
- i Department of Food Science (FOOD) , University of Copenhagen , Frederiksberg C , Denmark
| | - Anália Lourenço
- j Department of Computer Science , University of Vigo , Ourense , Spain
| | - Filipe Mergulhão
- b LEPABE, Department of Chemical Engineering, Faculty of Engineering , University of Porto , Porto , Portugal
| | - Rikke Louise Meyer
- k Aarhus University, Interdisciplinary Nanoscience Center (iNANO) , Aarhus , Denmark
| | - George Nychas
- l Agricultural University of Athens, Lab of Microbiology and Biotechnology of Foods , Athens , Greece
| | - Manuel Simões
- b LEPABE, Department of Chemical Engineering, Faculty of Engineering , University of Porto , Porto , Portugal
| | - Odile Tresse
- m LUNAM Université, Oniris, SECALIM UMR1024 INRA , Université de Nantes , Nantes , France
| | - Claus Sternberg
- n Department of Biotechnology and Biomedicine , Technical University of Denmark , Lyngby, Denmark
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21
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Liu Y, Mi Z, Niu W, An X, Yuan X, Liu H, Wang Y, Feng Y, Huang Y, Zhang X, Zhang Z, Fan H, Peng F, Li P, Tong Y, Bai C. Potential of a lytic bacteriophage to disrupt Acinetobacter baumannii biofilms in vitro. Future Microbiol 2016; 11:1383-1393. [PMID: 27538011 DOI: 10.2217/fmb-2016-0104] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
AIM The ability of Acinetobacter baumannii to form biofilms and develop antibiotic resistance makes it difficult to control infections caused by this bacterium. In this study, we explored the potential of a lytic bacteriophage to disrupt A. baumannii biofilms. MATERIALS & METHODS The potential of the lytic bacteriophage to disrupt A. baumannii biofilms was assessed by performing electron microscopy, live/dead bacterial staining, crystal violet staining and by determining adenosine triphosphate release. RESULTS The bacteriophage inhibited the formation of and disrupted preformed A. baumannii biofilms. Results of disinfection assay showed that the lytic bacteriophage lysed A. baumannii cells suspended in blood or grown on metal surfaces. CONCLUSION These results suggest the potential of the lytic bacteriophage to disrupt A. baumannii biofilms.
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Affiliation(s)
- Yannan Liu
- Department of Graduate, Hebei North University, Zhangjiakou, Hebei 075000, China.,Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Zhiqiang Mi
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Wenkai Niu
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Xiaoping An
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Xin Yuan
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Huiying Liu
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Yong Wang
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Yuzhong Feng
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Yong Huang
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Xianglilan Zhang
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Zhiyi Zhang
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Hang Fan
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Fan Peng
- Department of Respiratory Medicine, the First Hospital of Changsha, Changsha, Hunan 410000, China
| | - Puyuan Li
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
| | - Yigang Tong
- Department of Microbiological Omics and Bioinformatics, State Key Laboratory of Pathogen & Biosecurity, Beijing Institute of Microbiology & Epidemiology, Beijing 100071, China
| | - Changqing Bai
- Department of Respiratory & Critical Care Diseases, 307th Hospital of PLA, Beijing 100071, China
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22
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Abdulkareem AF, Lee HH, Ahmadi M, Martinez LR. Fungal serotype-specific differences in bacterial-yeast interactions. Virulence 2016; 6:652-7. [PMID: 26132337 DOI: 10.1080/21505594.2015.1066962] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Cryptococcus neoformans (Cn) causes meningoencephalitis in immunocompromised individuals. This encapsulated fungus can be found interacting with environmental microbes in soil contaminated with pigeon excrement. Cn survival within polymicrobial and other challenging communities has been shown to affect the evolution of its virulence factors. We compared the survival of 10 serotype A and D strains after interaction with the soil bacterium, Acinetobacter baumannii (Ab). Although co-incubation with Ab stimulated virulence factors production by strains of both cryptococcal serotypes, on average, serotype A strains displayed significantly higher survival rate, number of metabolically active cells within biofilms, and capsular polysaccharide production and release than serotype D strains. Our findings suggest that interactions of Cn with other microorganisms influence the fungus' regulation and production of virulence factors, important elements needed for the successful colonization of the human host.
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Affiliation(s)
- Asan F Abdulkareem
- a Department of Biology ; Faculty of Sciences and Health ; Koya University , Koya-Erbil , Iraq
| | - Hiu Ham Lee
- b Department of Biomedical Sciences ; NYIT College of Osteopathic Medicine ; New York Institute of Technology , Old Westbury , NY USA
| | - Mohammed Ahmadi
- c Department of Biology ; Adelphi University , Garden City , NY USA
| | - Luis R Martinez
- b Department of Biomedical Sciences ; NYIT College of Osteopathic Medicine ; New York Institute of Technology , Old Westbury , NY USA
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23
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Narayanan A, Nair MS, Karumathil DP, Baskaran SA, Venkitanarayanan K, Amalaradjou MAR. Inactivation of Acinetobacter baumannii Biofilms on Polystyrene, Stainless Steel, and Urinary Catheters by Octenidine Dihydrochloride. Front Microbiol 2016; 7:847. [PMID: 27375572 PMCID: PMC4899441 DOI: 10.3389/fmicb.2016.00847] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 05/22/2016] [Indexed: 11/13/2022] Open
Abstract
Acinetobacter baumannii is a major nosocomial pathogen causing human infections with significant mortality rates. In most cases, infections are acquired through exposure to A. baumannii biofilms that persist on contaminated hospital equipment and surfaces. Thus, it is imperative to develop effective measures for controlling A. baumannii biofilms in nosocomial settings. This study investigated the efficacy of octenidine dihydrochloride (OH), a new generation disinfectant for reducing A. baumannii biofilms on polystyrene, stainless steel and catheters. OH at 0.3% (5 mM), 0.6% (10 mM), and 0.9% (15 mM) was effective in significantly inactivating A. baumannii biofilms on all tested surfaces (P < 0.05). Furthermore, OH was equally effective in inactivating biofilms of multidrug resistant and drug susceptible A. baumannii isolates. In addition, confocal imaging revealed the predominance of dead cells in the OH-treated samples in comparison to the control. Further, scanning electron microscopy of biofilms formed on catheters revealed that OH treatment significantly reduced A. baumannii biofilm populations in corroboration with our antibiofilm assay. These data underscore the efficacy of OH in inactivating A. baumannii biofilms, thereby suggesting its potential use as a disinfectant or a catheter lock solution to control A. baumannii infections.
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Affiliation(s)
- Amoolya Narayanan
- Department of Psychological Sciences, University of Connecticut, Storrs CT, USA
| | - Meera S Nair
- Department of Animal Science, University of Connecticut, Storrs CT, USA
| | | | - Sangeetha A Baskaran
- Department of Veterinary Public Health and Epidemiology, Veterinary College and Research Institute Thanjavur, India
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24
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Dahdouh E, Orgaz B, Gómez-Gil R, Mingorance J, Daoud Z, Suarez M, San Jose C. Patterns of biofilm structure and formation kinetics among Acinetobacter baumannii clinical isolates with different antibiotic resistance profiles. MEDCHEMCOMM 2016. [DOI: 10.1039/c5md00377f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This study evaluates the rates of biofilm formation in light of the different characteristics of twelve A. baumannii clinical isolates.
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Affiliation(s)
- E. Dahdouh
- Faculty of Veterinary
- Department of Animal Health
- University Complutense of Madrid
- Madrid
- Spain
| | - B. Orgaz
- Faculty of Veterinary
- Department of Food Science and Technology
- University Complutense of Madrid
- Madrid
- Spain
| | - R. Gómez-Gil
- Servicio de Microbiología
- Hospital Universitario La Paz
- IdiPAZ
- Madrid
- Spain
| | - J. Mingorance
- Servicio de Microbiología
- Hospital Universitario La Paz
- IdiPAZ
- Madrid
- Spain
| | - Z. Daoud
- Faculty of Medicine and Medical Sciences
- Department of Clinical Microbiology
- University of Balamand
- Amioun
- Lebanon
| | - M. Suarez
- Faculty of Veterinary
- Department of Animal Health
- University Complutense of Madrid
- Madrid
- Spain
| | - C. San Jose
- Faculty of Veterinary
- Department of Food Science and Technology
- University Complutense of Madrid
- Madrid
- Spain
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25
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Grguric-Smith LM, Lee HH, Gandhi JA, Brennan MB, DeLeon-Rodriguez CM, Coelho C, Han G, Martinez LR. Neutropenia exacerbates infection by Acinetobacter baumannii clinical isolates in a murine wound model. Front Microbiol 2015; 6:1134. [PMID: 26528277 PMCID: PMC4607880 DOI: 10.3389/fmicb.2015.01134] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 10/02/2015] [Indexed: 01/21/2023] Open
Abstract
The Gram negative coccobacillus Acinetobacter baumannii has become an increasingly prevalent cause of hospital-acquired infections in recent years. The majority of clinical A. baumannii isolates display high-level resistance to antimicrobials, which severely compromises our capacity to care for patients with A. baumannii disease. Neutrophils are of major importance in the host defense against microbial infections. However, the contribution of these cells of innate immunity in host resistance to cutaneous A. baumannii infection has not been directly investigated. Hence, we hypothesized that depletion of neutrophils increases severity of bacterial disease in an experimental A. baumannii murine wound model. In this study, the Ly-6G-specific monoclonal antibody (mAb), 1A8, was used to generate neutropenic mice and the pathogenesis of several A. baumannii clinical isolates on wounded cutaneous tissue was investigated. We demonstrated that neutrophil depletion enhances bacterial burden using colony forming unit determinations. Also, mAb 1A8 reduces global measurements of wound healing in A. baumannii-infected animals. Interestingly, histological analysis of cutaneous tissue excised from A. baumannii-infected animals treated with mAb 1A8 displays enhanced collagen deposition. Furthermore, neutropenia and A. baumannii infection alter pro-inflammatory cytokine release leading to severe microbial disease. Our findings provide a better understanding of the impact of these innate immune cells in controlling A. baumannii skin infections.
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Affiliation(s)
| | - Hiu H Lee
- Department of Biomedical Sciences, Long Island University-Post Brookville, NY, USA ; Department of Biomedical Sciences, College of Osteopathic Medicine, New York Institute of Technology Old Westbury, NY, USA
| | - Jay A Gandhi
- Department of Biomedical Sciences, Long Island University-Post Brookville, NY, USA
| | - Melissa B Brennan
- Department of Biomedical Sciences, Long Island University-Post Brookville, NY, USA
| | | | - Carolina Coelho
- Centre for Molecular & Cellular Biology of Inflammation, Kings College London, UK
| | - George Han
- Montefiore Medical Center, Division of Dermatology, Department of Medicine Bronx, NY, USA
| | - Luis R Martinez
- Department of Biomedical Sciences, College of Osteopathic Medicine, New York Institute of Technology Old Westbury, NY, USA
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26
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Microbicides Alter the Expression and Function of RND-Type Efflux Pump AdeABC in Biofilm-Associated Cells of Acinetobacter baumannii Clinical Isolates. Antimicrob Agents Chemother 2015; 60:57-63. [PMID: 26459900 DOI: 10.1128/aac.01045-15] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Accepted: 10/03/2015] [Indexed: 11/20/2022] Open
Abstract
Acinetobacter baumannii is a Gram-negative bacterium that causes nosocomial infections worldwide. This microbe's propensity to form biofilms allows it to persist and to survive on clinical abiotic surfaces for long periods. In fact, A. baumannii biofilm formation and its multidrug-resistant nature severely compromise our capacity to care for patients in hospital environments. In contrast, microbicides such as cetrimide (CT) and chlorhexidine (CHX) play important roles in the prevention and treatment of infections. We assessed the efficacy of CT and CHX, either alone or in combination, in eradicating A. baumannii biofilms formed by clinical isolates, by using stainless steel washers to mimic hard abiotic surfaces found in hospital settings. We demonstrated that increasing amounts of each microbicide, alone or in combination, were able to damage and to reduce the viability of A. baumannii biofilms efficaciously. Interestingly, the adeB gene of the resistance-nodulation-cell division (RND) family is predominantly associated with acquired resistance to antimicrobials in A. baumannii. We showed that CT and CHX adversely modified the expression and function of the RND-type efflux pump AdeABC in biofilm-associated A. baumannii cells. Furthermore, we established that these microbicides decreased the negative charges on A. baumannii cell membranes, causing dysregulation of the efflux pump and leading to cell death. Our findings suggest that CT and CHX, alone or in combination, can be used efficaciously for eradication of A. baumannii from hospital surfaces, in order to reduce infections caused by this nosocomial agent.
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27
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Flynn PB, Higginbotham S, Alshraiedeh NH, Gorman SP, Graham WG, Gilmore BF. Bactericidal efficacy of atmospheric pressure non-thermal plasma (APNTP) against the ESKAPE pathogens. Int J Antimicrob Agents 2015; 46:101-7. [PMID: 25963338 DOI: 10.1016/j.ijantimicag.2015.02.026] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 02/24/2015] [Accepted: 02/25/2015] [Indexed: 01/21/2023]
Abstract
The emergence of multidrug-resistant pathogens within the clinical environment is presenting a mounting problem in hospitals worldwide. The 'ESKAPE' pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) have been highlighted as a group of causative organisms in a majority of nosocomial infections, presenting a serious health risk due to widespread antimicrobial resistance. The stagnating pipeline of new antibiotics requires alternative approaches to the control and treatment of nosocomial infections. Atmospheric pressure non-thermal plasma (APNTP) is attracting growing interest as an alternative infection control approach within the clinical setting. This study presents a comprehensive bactericidal assessment of an in-house-designed APNTP jet both against biofilms and planktonic bacteria of the ESKAPE pathogens. Standard plate counts and the XTT metabolic assay were used to evaluate the antibacterial effect of APNTP, with both methods demonstrating comparable eradication times. APNTP exhibited rapid antimicrobial activity against all of the ESKAPE pathogens in the planktonic mode of growth and provided efficient and complete eradication of ESKAPE pathogens in the biofilm mode of growth within 360s, with the exception of A. baumannii where a >4log reduction in biofilm viability was observed. This demonstrates its effectiveness as a bactericidal treatment against these pathogens and further highlights its potential application in the clinical environment for the control of highly antimicrobial-resistant pathogens.
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Affiliation(s)
- Padrig B Flynn
- School of Pharmacy, Queen's University of Belfast, Belfast BT9 7BL, UK
| | | | - Nid'a H Alshraiedeh
- School of Pharmacy, Queen's University of Belfast, Belfast BT9 7BL, UK; Faculty of Pharmacy, Jordan University of Science and Technology, Irbid 22110, Jordan
| | - Sean P Gorman
- School of Pharmacy, Queen's University of Belfast, Belfast BT9 7BL, UK
| | - William G Graham
- Centre for Plasma Physics, Queen's University of Belfast, Belfast BT7 1NN, UK
| | - Brendan F Gilmore
- School of Pharmacy, Queen's University of Belfast, Belfast BT9 7BL, UK.
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