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Ullah A, Mirani ZA, Binbin S, Wang F, Chan MWH, Aslam S, Yonghong L, Hassan N, Naveed M, Hussain S, Khatoon Z. An Elucidative Study of the Anti-biofilm Effect of Selenium Nanoparticles (SeNPs) on Selected Biofilm Producing Pathogenic Bacteria: A Disintegrating Effect of SeNPs on Bacteria. Process Biochem 2023. [DOI: 10.1016/j.procbio.2022.12.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Beadell BA, Chieng A, Parducho KR, Dai Z, Ho SO, Fujii G, Wang Y, Porter E. Nano- and Macroscale Imaging of Cholesterol Linoleate and Human Beta Defensin 2-Induced Changes in Pseudomonas aeruginosa Biofilms. Antibiotics (Basel) 2021; 10:antibiotics10111279. [PMID: 34827217 PMCID: PMC8615053 DOI: 10.3390/antibiotics10111279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 10/13/2021] [Accepted: 10/16/2021] [Indexed: 11/16/2022] Open
Abstract
The biofilm production of Pseudomonas aeruginosa (PA) is central to establishing chronic infection in the airways in cystic fibrosis. Epithelial cells secrete an array of innate immune factors, including antimicrobial proteins and lipids, such as human beta defensin 2 (HBD2) and cholesteryl lineolate (CL), respectively, to combat colonization by pathogens. We have recently shown that HBD2 inhibits biofilm production by PA, possibly linked to interference with the transport of biofilm precursors. Considering that both HBD2 and CL are increased in airway fluids during infection, we hypothesized that CL synergizes with HBD2 in biofilm inhibition. CL was formulated in phospholipid-based liposomes (CL-PL). As measured by atomic force microscopy of single bacteria, CL-PL alone and in combination with HBD2 significantly increased bacterial surface roughness. Additionally, extracellular structures emanated from untreated bacterial cells, but not from cells treated with CL-PL and HBD2 alone and in combination. Crystal violet staining of the biofilm revealed that CL-PL combined with HBD2 effected a significant decrease of biofilm mass and increased the number of larger biofilm particles consistent with altered cohesion of formed biofilms. These data suggest that CL and HBD2 affect PA biofilm formation at the single cell and community-wide level and that the community-wide effects of CL are enhanced by HBD2. This research may inform future novel treatments for recalcitrant infections in the airways of CF patients.
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Affiliation(s)
- Brent A. Beadell
- Department of Biological Sciences, California State University Los Angeles, Los Angeles, CA 90032, USA; (B.A.B.); (K.R.P.)
| | - Andy Chieng
- Department of Chemistry and Biochemistry, California State University Los Angeles, Los Angeles, CA 90032, USA; (A.C.); (Y.W.)
| | - Kevin R. Parducho
- Department of Biological Sciences, California State University Los Angeles, Los Angeles, CA 90032, USA; (B.A.B.); (K.R.P.)
| | - Zhipeng Dai
- Molecular Express, Inc., Rancho Dominguez, CA 90220, USA; (Z.D.); (S.O.H.); (G.F.)
| | - Sam On Ho
- Molecular Express, Inc., Rancho Dominguez, CA 90220, USA; (Z.D.); (S.O.H.); (G.F.)
| | - Gary Fujii
- Molecular Express, Inc., Rancho Dominguez, CA 90220, USA; (Z.D.); (S.O.H.); (G.F.)
| | - Yixian Wang
- Department of Chemistry and Biochemistry, California State University Los Angeles, Los Angeles, CA 90032, USA; (A.C.); (Y.W.)
| | - Edith Porter
- Department of Biological Sciences, California State University Los Angeles, Los Angeles, CA 90032, USA; (B.A.B.); (K.R.P.)
- Correspondence: ; Tel.: +1-323-343-6353
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Ojha P, Kar NP, Nayak S, Patra AK, Sahoo KK. Isolation of a broad spectrum antimicrobial producing thermophilic Bacillus and characterization of its antimicrobial protein. Arch Microbiol 2021; 203:2059-2073. [PMID: 33575852 DOI: 10.1007/s00203-020-02162-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 11/23/2020] [Accepted: 12/27/2020] [Indexed: 10/22/2022]
Abstract
The hot spring water of Atri in India was believed to have disease curing property. An antibacterial producing organism was isolated and identified as Bacillus paralicheniformis by morphology, microscopy, and 16S-rRNA. Its secretion inhibited bacteria, yeast, and fungus in well-diffusion-method. The secreted antimicrobial was a 16.74 kDa protein homologous of chicken-lysozyme-C. The novel lysozyme's activities were recorded under different parameters. It was active from pH 5-9 and endured up to 60 °C for 120 min. Complete cell wall lysis of S. flexneri and P. aeruginosa was observed under a microscope at 4500× with a minimum inhibitory concentration of 7.8 µg/ml, while others required a higher dose, i.e., 13 µg/ml, and 20 µg/ml for E.coli and S. typhimurium, respectively. The discovered lysozyme has the extraordinary potential to lyse Gram-positive bacteria, yeast, fungus, and more efficiently lyse chick-lysozyme-C resistant lipopolysaccharide rich Gram-negative bacteria's outer cell wall.
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Affiliation(s)
- Purusottam Ojha
- Department of Botany and Biotechnology, Ravenshaw University, Cuttack, Odisha, India, 753003.,Imgenex India Pvt. Ltd, E5 Infocity, Chandka Industrial Estate, KIIT Post Office, Bhubaneswar, Odisha, India, 751024
| | | | - Shreenath Nayak
- Imgenex India Pvt. Ltd, E5 Infocity, Chandka Industrial Estate, KIIT Post Office, Bhubaneswar, Odisha, India, 751024
| | - Ashok Kumar Patra
- Imgenex India Pvt. Ltd, E5 Infocity, Chandka Industrial Estate, KIIT Post Office, Bhubaneswar, Odisha, India, 751024
| | - Khirod Kumar Sahoo
- Department of Botany and Biotechnology, Ravenshaw University, Cuttack, Odisha, India, 753003.
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Ayrapetyan ON, Obluchinskaya ED, Zhurishkina EV, Skorik YA, Lebedev DV, Kulminskaya AA, Lapina IM. Antibacterial Properties of Fucoidans from the Brown Algae Fucus vesiculosus L. of the Barents Sea. BIOLOGY 2021; 10:67. [PMID: 33477817 PMCID: PMC7832856 DOI: 10.3390/biology10010067] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 01/15/2021] [Indexed: 02/07/2023]
Abstract
Fucoidans, sulfated polysaccharides found in cell walls of brown algae, are considered as a promising antimicrobial component for various applications in medicine and the food industry. In this study, we compare the antibacterial properties of two fractions of fucoidan from the brown algae Fucus vesiculosus gathered in the littoral of the Barents Sea and sampled at different stages of purification. The crude fraction of fucoidan was isolated from algae by extraction with aqueous ethanol and sonication. The purified fraction was obtained by additional treatment of the crude fraction with a solution of calcium chloride. The structural features of both fractions were characterized in detail and their antibacterial effects against several Gram-positive and Gram-negative bacteria were compared by photometry, acridine orange staining assay, and atomic force microscopy. Fucoidan inhibited growth in all of the above microorganisms, showing a bacteriostatic effect with minimum inhibitory concentrations (MIC) in the range between 4 and 6 mg/mL, with E. coli being the most sensitive to both fractions. Changes in the chemical composition after treatment of the crude fraction with a solution of calcium chloride led to a decrease in the content of sulfates and uronic acids and diminished antibacterial activity.
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Affiliation(s)
- Olga N. Ayrapetyan
- Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia; (O.N.A.); (E.V.Z.); (D.V.L.); (A.A.K.)
- Kurchatov Genome Center—PNPI, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia
- Faculty of Biotechnologies, ITMO University, Kronverksky Prospekt 49, Building. A, 197101 Saint Petersburg, Russia
| | - Ekaterina D. Obluchinskaya
- Federal State Budgetary Scientific Institution of Murmansk Marine Biological Institute of the Russian Academy of Sciences (MMBI RAS), Vladimirskaya, 17, 183010 Murmansk, Russia;
| | - Elena V. Zhurishkina
- Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia; (O.N.A.); (E.V.Z.); (D.V.L.); (A.A.K.)
- Kurchatov Genome Center—PNPI, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia
| | - Yury A. Skorik
- Institute of Macromolecular Compounds of the Russian Academy of Sciences, Bolshoy Prospekt V.O. 31, 199004 Saint Petersburg, Russia;
| | - Dmitry V. Lebedev
- Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia; (O.N.A.); (E.V.Z.); (D.V.L.); (A.A.K.)
- National Research Centre Kurchatov Institute, Akademika Kurchatova Square 1, 123182 Moscow, Russia
| | - Anna A. Kulminskaya
- Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia; (O.N.A.); (E.V.Z.); (D.V.L.); (A.A.K.)
- Kurchatov Genome Center—PNPI, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia
| | - Irina M. Lapina
- Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Center “Kurchatov Institute”, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia; (O.N.A.); (E.V.Z.); (D.V.L.); (A.A.K.)
- Kurchatov Genome Center—PNPI, Mkr. Orlova Roshcha, 1, 188300 Gatchina, Russia
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Zamani E, Johnson TJ, Chatterjee S, Immethun C, Sarella A, Saha R, Dishari SK. Cationic π-Conjugated Polyelectrolyte Shows Antimicrobial Activity by Causing Lipid Loss and Lowering Elastic Modulus of Bacteria. ACS APPLIED MATERIALS & INTERFACES 2020; 12:49346-49361. [PMID: 33089982 PMCID: PMC8926324 DOI: 10.1021/acsami.0c12038] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Cationic, π-conjugated oligo-/polyelectrolytes (CCOEs/CCPEs) have shown great potential as antimicrobial materials to fight against antibiotic resistance. In this work, we treated wild-type and ampicillin-resistant (amp-resistant) Escherichia coli (E. coli) with a promising cationic, π-conjugated polyelectrolyte (P1) with a phenylene-based backbone and investigated the resulting morphological, mechanical, and compositional changes of the outer membrane of bacteria in great detail. The cationic quaternary amine groups of P1 led to electrostatic interactions with negatively charged moieties within the outer membrane of bacteria. Using atomic force microscopy (AFM), high-resolution transmission electron microscopy (TEM), we showed that due to this treatment, the bacterial outer membrane became rougher, decreased in stiffness/elastic modulus (AFM nanoindentation), formed blebs, and released vesicles near the cells. These evidences, in addition to increased staining of the P1-treated cell membrane by lipophilic dye Nile Red (confocal laser scanning microscopy (CLSM)), suggested loosening/disruption of packing of the outer cell envelope and release and exposure of lipid-based components. Lipidomics and fatty acid analysis confirmed a significant loss of phosphate-based outer membrane lipids and fatty acids, some of which are critically needed to maintain cell wall integrity and mechanical strength. Lipidomics and UV-vis analysis also confirmed that the extracellular vesicles released upon treatment (AFM) are composed of lipids and cationic P1. Such surface alterations (vesicle/bleb formation) and release of lipids/fatty acids upon treatment were effective enough to inhibit further growth of E. coli cells without completely disintegrating the cells and have been known as a defense mechanism of the cells against cationic antimicrobial agents.
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Affiliation(s)
- Ehsan Zamani
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Tyler J. Johnson
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Shyambo Chatterjee
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Cheryl Immethun
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Anandakumar Sarella
- Nebraska Center for Materials and Nanoscience, Voelte-Keegan Nanoscience Research Center, University of Nebraska-Lincoln, Lincoln, NE 68588-0298, United States
| | - Rajib Saha
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Shudipto Konika Dishari
- Department of Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
- Corresponding author’s ; Phone: 402-472-7537
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Browne K, Chakraborty S, Chen R, Willcox MDP, Black DS, Walsh WR, Kumar N. A New Era of Antibiotics: The Clinical Potential of Antimicrobial Peptides. Int J Mol Sci 2020; 21:ijms21197047. [PMID: 32987946 PMCID: PMC7582481 DOI: 10.3390/ijms21197047] [Citation(s) in RCA: 202] [Impact Index Per Article: 50.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 09/22/2020] [Accepted: 09/22/2020] [Indexed: 12/13/2022] Open
Abstract
Antimicrobial resistance is a multifaceted crisis, imposing a serious threat to global health. The traditional antibiotic pipeline has been exhausted, prompting research into alternate antimicrobial strategies. Inspired by nature, antimicrobial peptides are rapidly gaining attention for their clinical potential as they present distinct advantages over traditional antibiotics. Antimicrobial peptides are found in all forms of life and demonstrate a pivotal role in the innate immune system. Many antimicrobial peptides are evolutionarily conserved, with limited propensity for resistance. Additionally, chemical modifications to the peptide backbone can be used to improve biological activity and stability and reduce toxicity. This review details the therapeutic potential of peptide-based antimicrobials, as well as the challenges needed to overcome in order for clinical translation. We explore the proposed mechanisms of activity, design of synthetic biomimics, and how this novel class of antimicrobial compound may address the need for effective antibiotics. Finally, we discuss commercially available peptide-based antimicrobials and antimicrobial peptides in clinical trials.
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Affiliation(s)
- Katrina Browne
- School of Chemistry, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia; (K.B.); (S.C.); (R.C.)
| | - Sudip Chakraborty
- School of Chemistry, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia; (K.B.); (S.C.); (R.C.)
| | - Renxun Chen
- School of Chemistry, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia; (K.B.); (S.C.); (R.C.)
| | - Mark DP Willcox
- School of Optometry and Vision Science, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia;
| | - David StClair Black
- School of Chemistry, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia; (K.B.); (S.C.); (R.C.)
- Correspondence: (D.S.B.); (N.K.); Tel.: +612-9385-4657 (D.S.B.); +612-9385-4698 (N.K.)
| | - William R Walsh
- Surgical and Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, Prince of Wales Hospital, University of New South Wales (UNSW), Randwick 2031, Australia;
| | - Naresh Kumar
- School of Chemistry, University of New South Wales (UNSW) Sydney, Sydney 2052, Australia; (K.B.); (S.C.); (R.C.)
- Correspondence: (D.S.B.); (N.K.); Tel.: +612-9385-4657 (D.S.B.); +612-9385-4698 (N.K.)
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Theansungnoen T, Jangpromma N, Anwised P, Daduang S, Fukumori Y, Taoka A, Klaynongsruang S. Membranolytic Effects of KT2 on Gram-Negative Escherichia coli Evaluated by Atomic Force Microscopy. APPL BIOCHEM MICRO+ 2019. [DOI: 10.1134/s0003683819050144] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Yadav K, Yavvari PS, Pal S, Kumar S, Mishra D, Gupta S, Mitra M, Soni V, Khare N, Sharma P, Srikanth CV, Kapil A, Singh A, Nandicoori VK, Bajaj A. Oral Delivery of Cholic Acid-Derived Amphiphile Helps in Combating Salmonella-Mediated Gut Infection and Inflammation. Bioconjug Chem 2019; 30:721-732. [DOI: 10.1021/acs.bioconjchem.8b00880] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Kavita Yadav
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
- Manipal Academy of Higher Education, Manipal-576104, Karnataka, India
| | - Prabhu Srinivas Yavvari
- Department of Chemistry, Indian Institute of Science Education and Research, Bhopal-462026, Madhya Pradesh, India
| | - Sanjay Pal
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
- Kalinga Institute of Industrial Technology, Bhubaneswar-751024, Odisha India,
| | - Sandeep Kumar
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
- Manipal Academy of Higher Education, Manipal-576104, Karnataka, India
| | - Deepakkumar Mishra
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
| | - Siddhi Gupta
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
| | - Madhurima Mitra
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
| | - Vijay Soni
- National Institute of Immunology, Aruna Asaf Ali
Marg, New Delhi-110067, India
| | - Neha Khare
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
| | - Priyanka Sharma
- Department of Microbiology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi-110029, India
| | - Chittur V. Srikanth
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
| | - Arti Kapil
- Department of Microbiology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi-110029, India
| | - Archana Singh
- CSIR-Institute of Genomics and Integrative Biology, Mathura Road, New Delhi-110025, India
| | | | - Avinash Bajaj
- Laboratory of Nanotechnology and Chemical Biology, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Third Milestone, Faridabad-Gurgaon
Expressway, Faridabad-121001, Haryana, India
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He M, Zhou Y, Nie S, Lu P, Xiao H, Tong Y, Liao Q, Wang R. Synthesis of Amphiphilic Copolymers Containing Ciprofloxacin and Amine Groups and Their Antimicrobial Performances As Revealed by Confocal Laser-Scanning Microscopy and Atomic-Force Microscopy. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2018; 66:8406-8414. [PMID: 30016099 DOI: 10.1021/acs.jafc.8b01759] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Two series of amphiphilic antimicrobial copolymers containing ciprofloxacin (CPF) and amine functional groups have been synthesized via free-radical copolymerization. The chemical structures of the different amine groups and the copolymer compositions have been systematically varied to study how the structure of the copolymer exerts an influence on the antibacterial activity. The viability of Escherichia coli in the presence of antimicrobial copolymers was observed by confocal laser-scanning microscopy (CLSM). CLSM as well as atomic-force microscopy (AFM) were applied to visualize changes in morphology of bacteria treated with antimicrobial copolymers and elucidate the antimicrobial mechanism of the antimicrobial copolymers. Morphological changes of bacteria observed via AFM and CLSM demonstrated that the antibacterial mechanism was due to the disruption of the bacterial membrane. The destruction of the cell membrane was also confirmed by the leakage of intracellular components, which had a strong absorbance at 260 nm. The inhibitory process was monitored by UV absorption dynamically.
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Affiliation(s)
- Man He
- School of Chemistry and Chemical Engineering , Southeast University , Nanjing 211189 , China
- Guangxi Key Laboratory of Clean Pulp and Papermaking and Pollution Control, College of Light Industry and Food Engineering , Guangxi University , Nanning 530004 , China
| | - Yuming Zhou
- School of Chemistry and Chemical Engineering , Southeast University , Nanjing 211189 , China
| | - Shuangxi Nie
- Guangxi Key Laboratory of Clean Pulp and Papermaking and Pollution Control, College of Light Industry and Food Engineering , Guangxi University , Nanning 530004 , China
| | - Peng Lu
- Guangxi Key Laboratory of Clean Pulp and Papermaking and Pollution Control, College of Light Industry and Food Engineering , Guangxi University , Nanning 530004 , China
| | - Huining Xiao
- Department of Chemical Engineering and Limerick Pulp and Paper Centre , University of New Brunswick , Fredericton , NB E3B 5A3 , Canada
| | - Yuan Tong
- School of Chemistry and Chemical Engineering , Southeast University , Nanjing 211189 , China
| | - Qiang Liao
- School of Chemistry and Chemical Engineering , Southeast University , Nanjing 211189 , China
| | - Ruili Wang
- School of Chemistry and Chemical Engineering , Southeast University , Nanjing 211189 , China
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Dinarelli S, Girasole M, Longo G. Methods for Atomic Force Microscopy of Biological and Living Specimens. Methods Mol Biol 2018; 1814:529-539. [PMID: 29956253 DOI: 10.1007/978-1-4939-8591-3_31] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Two main precautions must be taken into account to obtain high-resolution morphological and nanomechanical characterization of biological specimens with an atomic force microscope: the tip-sample interaction and the sample-substrate adhesion. In this chapter we discuss the necessary steps for a correct preparation of three types of biological samples: erythrocytes, bacteria, and osteoblasts. The main goal is to deliver reproducible protocols to produce good cellular adhesion and minimizing the morphological alterations of the specimens.
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Affiliation(s)
- Simone Dinarelli
- Istituto di Struttura della Materia ISM - CNR, Via del Fosso del Cavaliere 100, Rome, Italy
| | - Marco Girasole
- Istituto di Struttura della Materia ISM - CNR, Via del Fosso del Cavaliere 100, Rome, Italy
| | - Giovanni Longo
- Istituto di Struttura della Materia ISM - CNR, Via del Fosso del Cavaliere 100, Rome, Italy.
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The antimicrobial effects of the alginate oligomer OligoG CF-5/20 are independent of direct bacterial cell membrane disruption. Sci Rep 2017; 7:44731. [PMID: 28361894 PMCID: PMC5374485 DOI: 10.1038/srep44731] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 02/13/2017] [Indexed: 12/19/2022] Open
Abstract
Concerns about acquisition of antibiotic resistance have led to increasing demand for new antimicrobial therapies. OligoG CF-5/20 is an alginate oligosaccharide previously shown to have antimicrobial and antibiotic potentiating activity. We investigated the structural modification of the bacterial cell wall by OligoG CF-5/20 and its effect on membrane permeability. Binding of OligoG CF-5/20 to the bacterial cell surface was demonstrated in Gram-negative bacteria. Permeability assays revealed that OligoG CF-5/20 had virtually no membrane-perturbing effects. Lipopolysaccharide (LPS) surface charge and aggregation were unaltered in the presence of OligoG CF-5/20. Small angle neutron scattering and circular dichroism spectroscopy showed no substantial change to the structure of LPS in the presence of OligoG CF-5/20, however, isothermal titration calorimetry demonstrated a weak calcium-mediated interaction. Metabolomic analysis confirmed no change in cellular metabolic response to a range of osmolytes when treated with OligoG CF-5/20. This data shows that, although weak interactions occur between LPS and OligoG CF-5/20 in the presence of calcium, the antimicrobial effects of OligoG CF-5/20 are not related to the induction of structural alterations in the LPS or cell permeability. These results suggest a novel mechanism of action that may avoid the common route in acquisition of resistance via LPS structural modification.
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López-Jiménez L, Fusté E, Martínez-Garriga B, Arnabat-Domínguez J, Vinuesa T, Viñas M. Effects of photodynamic therapy on Enterococcus faecalis biofilms. Lasers Med Sci 2015; 30:1519-26. [PMID: 25917515 PMCID: PMC4475243 DOI: 10.1007/s10103-015-1749-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 03/20/2015] [Indexed: 11/30/2022]
Abstract
Microbial biofilms are involved in almost all infectious pathologies of the oral cavity. This has led to the search for novel therapies specifically aimed at biofilm elimination. In this study, we used atomic force microscopy (AFM) to visualize injuries and to determine surface roughness, as well as confocal laser scanning microscopy (CLSM) to enumerate live and dead bacterial cells, to determine the effects of photodynamic therapy (PDT) on Enterococcus faecalis biofilms. The AFM images showed that PDT consisting of methylene blue and a 670-nm diode laser (output power 280 mW during 30 s) or toluidine blue and a 628-nm LED light (output power 1000 mW during 30 s) induced severe damage, including cell lysis, to E. faecalis biofilms, with the former also causing an important increase in surface roughness. These observations were confirmed by the increase in dead cells determined using CLSM. Our results highlight the potential of PDT as a promising method to achieve successful oral disinfection.
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Affiliation(s)
- L López-Jiménez
- Laboratory of Molecular Microbiology and Antimicrobials, Department of Pathology and Experimental Therapeutics, Medical School, IDIBELL-University of Barcelona, Barcelona, Spain
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13
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Powell LC, Pritchard MF, Emanuel C, Onsøyen E, Rye PD, Wright CJ, Hill KE, Thomas DW. A Nanoscale Characterization of the Interaction of a Novel Alginate Oligomer with the Cell Surface and Motility ofPseudomonas aeruginosa. Am J Respir Cell Mol Biol 2014; 50:483-92. [DOI: 10.1165/rcmb.2013-0287oc] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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Antibiotic-induced modifications of the stiffness of bacterial membranes. J Microbiol Methods 2013; 93:80-4. [DOI: 10.1016/j.mimet.2013.01.022] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 01/31/2013] [Accepted: 01/31/2013] [Indexed: 11/23/2022]
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15
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Consuegra J, de Lima ME, Santos D, Sinisterra RD, Cortés ME. Peptides: β-cyclodextrin inclusion compounds as highly effective antimicrobial and anti-epithelial proliferation agents. J Periodontol 2013; 84:1858-68. [PMID: 23510146 DOI: 10.1902/jop.2013.120679] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
BACKGROUND The use of antimicrobial peptides (AMPs) as therapeutic agents for periodontal infections has great advantages, such as broad spectrum of action, low toxicity, and limited bacterial resistance. However, their practical use is limited because of the large amount of peptide required to exercise the microbicidal function. METHODS LyeTxI, LL37f, and KR12 cationic peptides were prepared with β-cyclodextrin (βCD) at 1:1 molar ratios. The susceptibility of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum were assessed in anaerobic conditions. Cytotoxicity assays were performed using osteoblast and Caco-2 epithelial cells, and hemolytic activity was assessed on rabbit erythrocytes at an absorbance of 414 nm. Parameters of surface roughness and electrical charge were established by atomic force microscopy and zeta (ζ) potential, respectively. RESULTS AMP/βCDs drastically decreased the peptide concentration required for activity against the bacteria tested. Moreover, AMPs associated with βCD were able to modify cell-surface parameters, such as roughness and ζ potential. On the other hand, AMP/βCD did not alter the degree of hemolysis induced by the pure AMPs. The effective concentration at half-maximum values of the peptides and compounds on osteoblasts were greater than the concentrations required to achieve inhibition of bacterial growth in all the species tested. AMP/βCDs inhibited the proliferation of Caco-2 epithelial cells in a more efficient manner than AMPs alone. CONCLUSION AMP/βCD compounds more effectively inhibit periodontopathogenic bacteria than AMPs alone, with the additional ability of inhibiting the proliferation of epithelial cells at concentrations that are non-cytotoxic for osteoblasts and erythrocytes.
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Affiliation(s)
- Jessika Consuegra
- Department of Physiology and Biophysics, Biologic Science Institute (ICB), Federal University of Minas Gerais, Belo Horizonte, MG, Brazil
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Kasas S, Radotic K, Longo G, Saha B, Alonso-Sarduy L, Dietler G, Roduit C. A universal fluid cell for the imaging of biological specimens in the atomic force microscope. Microsc Res Tech 2013; 76:357-63. [PMID: 23390022 DOI: 10.1002/jemt.22174] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Accepted: 12/30/2012] [Indexed: 11/06/2022]
Abstract
Recently, atomic force microscope (AFM) manufacturers have begun producing instruments specifically designed to image biological specimens. In most instances, they are integrated with an inverted optical microscope, which permits concurrent optical and AFM imaging. An important component of the set-up is the imaging chamber, whose design determines the nature of the experiments that can be conducted. Many different imaging chamber designs are available, usually designed to optimize a single parameter, such as the dimensions of the substrate or the volume of fluid that can be used throughout the experiment. In this report, we present a universal fluid cell, which simultaneously optimizes all of the parameters that are important for the imaging of biological specimens in the AFM. This novel imaging chamber has been successfully tested using mammalian, plant, and microbial cells.
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Affiliation(s)
- Sandor Kasas
- Laboratoire de Physique de la Matière Vivante, EPFL, CH-1015, Lausanne, Switzerland.
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Chang KC, Chiang YW, Yang CH, Liou JW. Atomic force microscopy in biology and biomedicine. Tzu Chi Med J 2012. [DOI: 10.1016/j.tcmj.2012.08.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Ivanov IE, Morrison AE, Cobb JE, Fahey CA, Camesano TA. Creating antibacterial surfaces with the peptide chrysophsin-1. ACS APPLIED MATERIALS & INTERFACES 2012; 4:5891-5897. [PMID: 23043421 DOI: 10.1021/am301530a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Immobilization of antimicrobial peptides (AMPs) holds potential for creating surfaces with bactericidal properties. In order to successfully incorporate AMPs into desired materials, increased fundamental understanding of the relationship between AMP immobilization and the efficacy of bound peptides as antibacterial agents is required. In this study, we characterize the relationship between surface binding of the AMP and subsequent ability of the peptide to kill bacteria. Surface immobilization of the AMP chrysophsin-1 (CHY1) via a flexible linker is studied in real-time, using a quartz crystal microbalance with dissipation monitoring (QCM-D). Depending on whether the AMP is physically adsorbed to the surface or attached covalently via a zero-length or flexible cross-linker, changes could be observed in AMP orientation, surface density, flexibility, and activity against bacteria. Covalent surface binding of CHY1 led to the formation of solvated monolayers of vertically positioned peptide molecules, while the physical adsorption of CHY1 led to the deposition of rigid monolayers of horizontally positioned peptide molecules on the sensor surface. Covalently bound peptides were not removed by extensive washing and did not leach from the surface. Zero-length immobilization of the peptide decreased its ability to kill E. coli to 34% ± 7% of added bacteria, while binding via a flexible linker resulted in 82% ± 11% of bacteria being killed by the AMP.
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Affiliation(s)
- Ivan E Ivanov
- Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA
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Antimicrobial peptide trichokonin VI-induced alterations in the morphological and nanomechanical properties of Bacillus subtilis. PLoS One 2012; 7:e45818. [PMID: 23049870 PMCID: PMC3458079 DOI: 10.1371/journal.pone.0045818] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 08/22/2012] [Indexed: 11/19/2022] Open
Abstract
Antimicrobial peptides are promising alternative antimicrobial agents compared to conventional antibiotics. Understanding the mode of action is important for their further application. We examined the interaction between trichokonin VI, a peptaibol isolated from Trichoderma pseudokoningii, and Bacillus subtilis, a representative Gram-positive bacterium. Trichokonin VI was effective against B. subtilis with a minimal inhibitory concentration of 25 µM. Trichokonin VI exhibited a concentration- and time-dependent effect against B. subtilis, which was studied using atomic force microscopy. The cell wall of B. subtilis collapsed and the roughness increased upon treatment with trichokonin VI. Nanoindentation experiments revealed a progressive decrease in the stiffness of the cells. Furthermore, the membrane permeabilization effect of trichokonin VI on B. subtilis was monitored, and the results suggest that the leakage of intracellular materials is a possible mechanism of action for trichokonin VI, which led to alterations in the morphological and nanomechanical properties of B. subtilis.
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Longo G, Rio LM, Roduit C, Trampuz A, Bizzini A, Dietler G, Kasas S. Force volume and stiffness tomography investigation on the dynamics of stiff material under bacterial membranes. J Mol Recognit 2012; 25:278-84. [DOI: 10.1002/jmr.2171] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Giovanni Longo
- Laboratory of Physics of Living Matter; EPFL; Lausanne; Switzerland
| | - Laura Marques Rio
- Infectious Diseases Service, Department of Medicine; University Hospital Lausanne (CHUV); Lausanne; Switzerland
| | - Charles Roduit
- Laboratory of Physics of Living Matter; EPFL; Lausanne; Switzerland
| | - Andrej Trampuz
- Infectious Diseases Service, Department of Medicine; University Hospital Lausanne (CHUV); Lausanne; Switzerland
| | | | - Giovanni Dietler
- Laboratory of Physics of Living Matter; EPFL; Lausanne; Switzerland
| | - Sandor Kasas
- Laboratory of Physics of Living Matter; EPFL; Lausanne; Switzerland
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Liu S, Ng AK, Xu R, Wei J, Tan CM, Yang Y, Chen Y. Antibacterial action of dispersed single-walled carbon nanotubes on Escherichia coli and Bacillus subtilis investigated by atomic force microscopy. NANOSCALE 2010; 2:2744-2750. [PMID: 20877897 DOI: 10.1039/c0nr00441c] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Single-walled carbon nanotubes (SWCNTs) exhibit strong antibacterial activities. Direct contact between bacterial cells and SWCNTs may likely induce cell damages. Therefore, the understanding of SWCNT-bacteria interactions is essential in order to develop novel SWCNT-based materials for their potential environmental, imaging, therapeutic, and military applications. In this preliminary study, we utilized atomic force microscopy (AFM) to monitor dynamic changes in cell morphology and mechanical properties of two typical bacterial models (gram-negative Escherichia coli and gram-positive Bacillus subtilis) upon incubation with SWCNTs. The results demonstrated that individually dispersed SWCNTs in solution develop nanotube networks on the cell surface, and then destroy the bacterial envelopes with leakage of the intracellular contents. The cell morphology changes observed on air dried samples are accompanied by an increase in cell surface roughness and a decrease in surface spring constant. To mimic the collision between SWCNTs and cells, a sharp AFM tip of 2 nm was chosen to introduce piercings on the cell surface. No clear physical damages were observed if the applied force was below 10 nN. Further analysis also indicates that a single collision between one nanotube and a bacterial cell is unlikely to introduce direct physical damage. Hence, the antibacterial activity of SWCNTs is the accumulation effect of large amount of nanotubes through interactions between SWCNT networks and bacterial cells.
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Affiliation(s)
- Shaobin Liu
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459
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Tyagi AK, Malik A. Liquid and vapour-phase antifungal activities of selected essential oils against Candida albicans: microscopic observations and chemical characterization of Cymbopogon citratus. BMC COMPLEMENTARY AND ALTERNATIVE MEDICINE 2010; 10:65. [PMID: 21067604 PMCID: PMC2994787 DOI: 10.1186/1472-6882-10-65] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 11/10/2010] [Indexed: 12/16/2022]
Abstract
BACKGROUND Use of essential oils for controlling Candida albicans growth has gained significance due to the resistance acquired by pathogens towards a number of widely-used drugs. The aim of this study was to test the antifungal activity of selected essential oils against Candida albicans in liquid and vapour phase and to determine the chemical composition and mechanism of action of most potent essential oil. METHODS Minimum Inhibitory concentration (MIC) of different essential oils in liquid phase, assayed through agar plate dilution, broth dilution & 96-well micro plate dilution method and vapour phase activity evaluated through disc volatilization method. Reduction of C. albicans cells with vapour exposure was estimated by kill time assay. Morphological alteration in treated/untreated C. albicans cells was observed by the Scanning electron microscopy (SEM)/Atomic force microscopy (AFM) and chemical analysis of the strongest antifungal agent/essential oil has been done by GC, GC-MS. RESULTS Lemon grass (Cymbopogon citratus) essential oil exhibited the strongest antifungal effect followed by mentha (Mentha piperita) and eucalyptus (Eucalyptus globulus) essential oil. The MIC of lemon grass essential oil in liquid phase (288 mg/l) was significantly higher than that in the vapour phase (32.7 mg/l) and a 4 h exposure was sufficient to cause 100% loss in viability of C. albicans cells. SEM/AFM of C. albicans cells treated with lemon grass essential oil at MIC level in liquid and vapour phase showed prominent shrinkage and partial degradation, respectively, confirming higher efficacy of vapour phase. GC-MS analysis revealed that lemon grass essential oil was dominated by oxygenated monoterpenes (78.2%); α-citral or geranial (36.2%) and β-citral or neral (26.5%), monoterpene hydrocarbons (7.9%) and sesquiterpene hydrocarbons (3.8%). CONCLUSION Lemon grass essential oil is highly effective in vapour phase against C. albicans, leading to deleterious morphological changes in cellular structures and cell surface alterations.
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Affiliation(s)
- Amit K Tyagi
- Applied Microbiology Laboratory, Centre for Rural Development & Technology, Indian Institute of Technology Delhi, New Delhi- 110 016, India
| | - Anushree Malik
- Applied Microbiology Laboratory, Centre for Rural Development & Technology, Indian Institute of Technology Delhi, New Delhi- 110 016, India
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Strauss J, Kadilak A, Cronin C, Mello CM, Camesano TA. Binding, inactivation, and adhesion forces between antimicrobial peptide cecropin P1 and pathogenic E. coli. Colloids Surf B Biointerfaces 2010; 75:156-64. [DOI: 10.1016/j.colsurfb.2009.08.026] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Revised: 07/20/2009] [Accepted: 08/17/2009] [Indexed: 10/20/2022]
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Pini A, Falciani C, Mantengoli E, Bindi S, Brunetti J, Iozzi S, Rossolini GM, Bracci L. A novel tetrabranched antimicrobial peptide that neutralizes bacterial lipopolysaccharide and prevents septic shock in vivo. FASEB J 2009; 24:1015-22. [PMID: 19917670 DOI: 10.1096/fj.09-145474] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We describe the nonnatural antimicrobial peptide KKIRVRLSA (M33) and its capacity to neutralize LPS-induced cytokine release, preventing septic shock in animals infected with bacterial species of clinical interest. M33 showed strong resistance to proteolytic degradation when synthesized in tetrabranched form with 4 peptides linked by a lysine core, making it suitable for use in vivo. HPLC and mass spectrometry demonstrated its stability in serum beyond 24 h. M33 was found to be very selective for gram-negative bacteria. Minimal inhibitory concentration (MIC) ranged from 0.3 to 3 muM for multidrug resistant clinical isolates of several pathogenic species, including Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. M33 neutralized LPS derived from P. aeruginosa and K. pneumoniae, and prevented TNF-alpha release from LPS-activated macrophages, with an EC(50) of 3.8e-8 M and 2.8e-7 M, respectively, as detected by sandwich ELISA. M33 activity was also tested in sepsis animal models. It averted septic shock symptoms due to Escherichia coli and P. aeruginosa in doses compatible with clinical use (5-25 mg/kg). These properties make tetrabranched M33 peptide a good candidate for the development of a new antibacterial drug.-Pini, A., Falciani, C., Mantengoli, E., Bindi, S., Brunetti, J., Iozzi, S., Rossolini, G. M., Bracci, L. A novel tetrabranched antimicrobial peptide that neutralizes bacterial lipopolysaccharide and prevents septic shock in vivo.
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Affiliation(s)
- Alessandro Pini
- University of Siena, Molecular Biology Department, Section of Biochemistry, Via Fiorentina 1, 53100, Siena, Italy.
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Atomic force microscopy investigation of the morphology and topography of colistin-heteroresistant Acinetobacter baumannii strains as a function of growth phase and in response to colistin treatment. Antimicrob Agents Chemother 2009; 53:4979-86. [PMID: 19786595 DOI: 10.1128/aac.00497-09] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The prevalence of infections caused by multidrug-resistant gram-negative Acinetobacter baumannii strains and the lack of novel antibiotics under development are posing a global dilemma, forcing a resurgence of the last-line antibiotic colistin. Our aim was to use atomic force microscopy (AFM) to investigate the morphology and topography of paired colistin-susceptible and -resistant cells from colistin-heteroresistant A. baumannii strains as a function of bacterial growth phase and colistin exposure. An optimal AFM bacterial sample preparation protocol was established and applied to examine three paired strains. Images revealed rod-shaped colistin-susceptible cells (1.65 +/- 0.27 microm by 0.98 +/- 0.07 microm) at mid-logarithmic phase, in contrast to spherical colistin-resistant cells (1.03 +/- 0.09 microm); the latter were also more diverse in appearance and exhibited a rougher surface topography (7.05 +/- 1.3 nm versus 11.4 +/- 2.5 nm for susceptible versus resistant, respectively). Cellular elongation up to approximately 18 microm at stationary phase was more commonly observed in susceptible strains, although these "worm-like" cells were also observed occasionally in the resistant population. The effects of colistin exposure on the cell surface of colistin-susceptible and -resistant cells were found to be similar; topographical changes were minor in response to 0.5 microg/ml colistin; however, at 4 microg/ml colistin, a significant degree of surface disruption was detected. At 32 microg/ml colistin, cellular clumping and surface smoothening were evident. Our study has demonstrated for the first time substantial morphological and topographical differences between colistin-susceptible and -resistant cells from heteroresistant A. baumannii strains. These results contribute to an understanding of colistin action and resistance in regard to this problematic pathogen.
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