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The Mycobacterium tuberculosis capsule: a cell structure with key implications in pathogenesis. Biochem J 2019; 476:1995-2016. [PMID: 31320388 PMCID: PMC6698057 DOI: 10.1042/bcj20190324] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 06/19/2019] [Accepted: 06/20/2019] [Indexed: 01/17/2023]
Abstract
Bacterial capsules have evolved to be at the forefront of the cell envelope, making them an essential element of bacterial biology. Efforts to understand the Mycobacterium tuberculosis (Mtb) capsule began more than 60 years ago, but the relatively recent development of mycobacterial genetics combined with improved chemical and immunological tools have revealed a more refined view of capsule molecular composition. A glycogen-like α-glucan is the major constituent of the capsule, with lower amounts of arabinomannan and mannan, proteins and lipids. The major Mtb capsular components mediate interactions with phagocytes that favor bacterial survival. Vaccination approaches targeting the mycobacterial capsule have proven successful in controlling bacterial replication. Although the Mtb capsule is composed of polysaccharides of relatively low complexity, the concept of antigenic variability associated with this structure has been suggested by some studies. Understanding how Mtb shapes its envelope during its life cycle is key to developing anti-infective strategies targeting this structure at the host-pathogen interface.
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Cationized Magnetoferritin Enables Rapid Labeling and Concentration of Gram-Positive and Gram-Negative Bacteria in Magnetic Cell Separation Columns. Appl Environ Microbiol 2016; 82:3599-3604. [PMID: 27060124 PMCID: PMC4959160 DOI: 10.1128/aem.00720-16] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 04/05/2016] [Indexed: 01/10/2023] Open
Abstract
In order to identify pathogens rapidly and reliably, bacterial capture and concentration from large sample volumes into smaller ones are often required. Magnetic labeling and capture of bacteria using a magnetic field hold great promise for achieving this goal, but the current protocols have poor capture efficiency. Here, we present a rapid and highly efficient approach to magnetic labeling and capture of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria using cationized magnetoferritin (cat-MF). Magnetic labeling was achieved within a 1-min incubation period with cat-MF, and 99.97% of the labeled bacteria were immobilized in commercially available magnetic cell separation (MACS) columns. Longer incubation times led to more efficient capture, with S. aureus being immobilized to a greater extent than E. coli. Finally, low numbers of magnetically labeled E. coli bacteria (<100 CFU per ml) were immobilized with 100% efficiency and concentrated 7-fold within 15 min. Therefore, our study provides a novel protocol for rapid and highly efficient magnetic labeling, capture, and concentration of both Gram-positive and Gram-negative bacteria. IMPORTANCE Antimicrobial resistance (AMR) is a significant global challenge. Rapid identification of pathogens will retard the spread of AMR by enabling targeted treatment with suitable agents and by reducing inappropriate antimicrobial use. Rapid detection methods based on microfluidic devices require that bacteria are concentrated from large volumes into much smaller ones. Concentration of bacteria is also important to detect low numbers of pathogens with confidence. Here, we demonstrate that magnetic separation columns capture small amounts of bacteria with 100% efficiency. Rapid magnetization was achieved by exposing bacteria to cationic magnetic nanoparticles, and magnetized bacteria were concentrated 7-fold inside the column. Thus, bacterial capture and concentration were achieved within 15 min. This approach could be extended to encompass the capture and concentration of specific pathogens, for example, by functionalizing magnetic nanoparticles with antibodies or small molecule probes.
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Alkyl-imidazolium glycosides: non-ionic-cationic hybrid surfactants from renewable resources. Carbohydr Res 2015; 412:28-33. [PMID: 26000863 DOI: 10.1016/j.carres.2015.04.022] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Accepted: 04/26/2015] [Indexed: 11/21/2022]
Abstract
A series of surfactants combining carbohydrate and imidazolium head groups were prepared and investigated on their assembly behavior. The presence of the imidazolium group dominated the interactions of the surfactants, leading to high CMCs and large molecular surface areas, reflected in curved rather than lamellar surfactant assemblies. The carbohydrate, on the other hand, stabilized molecular assemblies slightly and reduced the surface tension of surfactant solutions considerably. A comparative emulsion study discourages the use of pure alkyl imidazolium glycosides owing to reduced assembly stabilities compared with APGs. However, the surfactants are believed to have potential as component in carbohydrate based surfactant mixtures.
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Uria MJ, Zhang Q, Li Y, Chan A, Exley RM, Gollan B, Chan H, Feavers I, Yarwood A, Abad R, Borrow R, Fleck RA, Mulloy B, Vazquez JA, Tang CM. A generic mechanism in Neisseria meningitidis for enhanced resistance against bactericidal antibodies. J Exp Med 2008; 205:1423-34. [PMID: 18504306 PMCID: PMC2413038 DOI: 10.1084/jem.20072577] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The presence of serum bactericidal antibodies is a proven correlate of protection against systemic infection with the important human pathogen Neisseria meningitidis. We have identified three serogroup C N. meningitidis (MenC) isolates recovered from patients with invasive meningococcal disease that resist killing by bactericidal antibodies induced by the MenC conjugate vaccine. None of the patients had received the vaccine, which has been successfully introduced in countries in North America and Europe. The increased resistance was not caused by changes either in lipopolysaccharide sialylation or acetylation of the α2-9–linked polysialic acid capsule. Instead, the resistance of the isolates resulted from the presence of an insertion sequence, IS1301, in the intergenic region (IGR) between the sia and ctr operons, which are necessary for capsule biosynthesis and export, respectively. The insertion sequence led to an increase in the transcript levels of surrounding genes and the amount of capsule expressed by the strains. The increased amount of capsule was associated with down-regulation of the alternative pathway of complement activation, providing a generic mechanism by which the bacterium protects itself against bactericidal antibodies. The strains with IS1301 in the IGR avoided complement-mediated lysis in the presence of bactericidal antibodies directed at the outer membrane protein, PorA, or raised against whole cells.
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Affiliation(s)
- Maria Jose Uria
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
- Reference Laboratory for Neisseria, National Center of Microbiology, Institute of Health Carlos III, 28220 Majadahonda, Madrid, Spain
| | - Qian Zhang
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
| | - Yanwen Li
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
| | - Angel Chan
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
| | - Rachel M. Exley
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
| | - Bridget Gollan
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
| | - Hannah Chan
- National Institute of Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire EN6 3QG, England, UK
| | - Ian Feavers
- National Institute of Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire EN6 3QG, England, UK
| | - Andy Yarwood
- JEOL (UK) Ltd., JEOL House, Silvercourt, Watchmead, Welwyn Garden City, Hertfordshire AL7 1LT, England, UK
| | - Raquel Abad
- Reference Laboratory for Neisseria, National Center of Microbiology, Institute of Health Carlos III, 28220 Majadahonda, Madrid, Spain
| | - Ray Borrow
- Vaccine Evaluation Unit, North West Regional HPA Laboratory, Manchester Royal Infirmary, Manchester M13 9WZ, England, UK
| | - Roland A. Fleck
- National Institute of Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire EN6 3QG, England, UK
| | - Barbara Mulloy
- National Institute of Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire EN6 3QG, England, UK
| | - Julio A. Vazquez
- Reference Laboratory for Neisseria, National Center of Microbiology, Institute of Health Carlos III, 28220 Majadahonda, Madrid, Spain
| | - Christoph M. Tang
- Centre for Molecular Microbiology and Infection, Department of Microbiology, Imperial College London, London SW7 2AZ, England, UK
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Ukuku DO, Geveke DJ, Cooke P, Zhang HQ. Membrane damage and viability loss of Escherichia coli K-12 in apple juice treated with radio frequency electric field. J Food Prot 2008; 71:684-90. [PMID: 18468020 DOI: 10.4315/0362-028x-71.4.684] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of a radio frequency electric fields (RFEF) process. In order to understand the mechanism of inactivation of bacteria by RFEF, apple juice purchased from a wholesale distributor was inoculated with Escherichia coli K-12 at 7.8 log CFU/ml and then treated with RFEF. The inoculated apple juice was passed through an RFEF chamber operated at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min. Treatment condition was periodically adjusted to achieve outlet temperatures of 40, 45, 50, 55, and 60 degrees C. Samples at each outlet temperature were plated (0.1 ml) and the number of CFU per milliliter determined on nonselective and selective agar media was used to calculate the viability loss. Bacterial inactivation and viability loss occurred at all temperatures tested with 55 degrees C treatment, leading to 4-log reductions. No significant effect was observed on bacterial population in control samples treated at 55 degrees C with a low-RFEF (0.15 kV/cm) field strength. These observations suggest that the 4-log reduction in samples treated at 15 kV/cm was entirely due to nonthermal effect. RFEF treatment resulted in membrane damage of the bacteria, leading to the efflux of intracellular ATP and UV-absorbing materials. Populations of injured bacteria recovered immediately (<30 min) from the treated apple juice averaged 0.43 log and were below detection after 1 h of RFEF treatment and determination using selective plates (tryptic soy agar containing 5% sodium chloride). The results of this study suggest that mechanism of inactivation of RFEF is by disruption of the bacterial surface structure leading to the damage and leakage of intracellular biological active compounds.
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Affiliation(s)
- Dike O Ukuku
- Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA.
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Abstract
Five individual strains of Listeria monocytogenes and a mixed cocktail of all five were studied for attachment on frankfurters, ham, bologna, and roast beef relative to their cell surface characteristics. The ratio of strongly attached (sessile) L. monocytogenes cells compared with total (sessile and planktonic) attached cells on ready-to-eat meats was also determined. Because bacterial cell surfaces were characterized by net negative charge and hydrophobicity, electrostatic interaction chromatography and cationized ferritin methods were chosen to study net negative charge distribution on the bacterial cell surface, whereas hydrophobic interaction chromatography and contact angle measurement were used to examine the cell surface hydrophobicity. No differences (P > 0.05) were observed in cell surface charge or cell surface hydrophobicity among strains. Approximately 84 to 87% L. monocytogenes were found to attach strongly to ready-to-eat meats within 5 min. No differences (P > 0.05) were found among strains or among meats. Micrographs observed from scanning electron microscopy showed no differences among the strains but showed a difference in age of cells (mixed culture) in terms of surface negative charge distribution. More surface negatively charged sites were observed at 0 and 7 days and much fewer at 3 days during storage of washed, harvested cells in buffer at 4 degrees C (aged cells under cold and nutrient deprivation), indicating a possible change in cell surface properties. Because no difference in strains was observed, the contact angle measurement study was carried out with the five-strain mixed culture. The surface hydrophobicity increased in frankfurters, decreased in roast beef, and was unchanged in ham and bologna as a result of inoculation.
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Affiliation(s)
- Sally C C Foong
- Food Safety Research Laboratory, Department of Microbiology, Iowa State University, 207 Science 1, Ames, Iowa 50011, USA
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