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Schug AR, Bartel A, Meurer M, Scholtzek AD, Brombach J, Hensel V, Fanning S, Schwarz S, Feßler AT. Comparison of two methods for cell count determination in the course of biocide susceptibility testing. Vet Microbiol 2020; 251:108831. [PMID: 33202368 DOI: 10.1016/j.vetmic.2020.108831] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 08/20/2020] [Indexed: 10/23/2022]
Abstract
The inoculum density is an important parameter for numerous experimental approaches in bacteriology, including antimicrobial susceptibility testing (AST), biocide susceptibility testing (BST) and biocide efficacy testing (BET). Methods to determine the inoculum density commonly refer to cell counts and have been described for BET according to the German Medical Veterinary Society (Deutsche Veterinärmedizinische Gesellschaft, DVG) and for AST according to the Clinical and Laboratory Standards Institute (CLSI). In this study, the DVG method using 1000 μL volumes of two different dilution steps and the AST method according to CLSI using a 100 μL volume of a single dilution step from the inoculum suspension were compared. For this, each of the four reference strains, Staphylococcus aureus ATCC® 6538, Enterococcus hirae ATCC® 10541, Escherichia coli ATCC® 10536 and Pseudomonas aeruginosa ATCC® 15442, was comparatively tested 28 times using the inoculum preparation according to DVG. The results were statistically analysed using Bland-Altman plots and 95 % limits of agreement (AL). Moreover, cell counts were correlated with the optical density of the bacterial suspensions used. In comparison, the CLSI method measured lower values for colony-forming units (CFU) of -0.12 log10 compared to the DVG method. Overall, both methods returned an AL of -0.52 to 0.27 log10. Since the variations observed between the two methods were within one log10 step and the measured CFUs did not differ systematically, both methods proved to be suitable for cell count determination. Therefore, the CLSI method, which is less complex and less time-consuming, is recommended.
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Affiliation(s)
- Angela R Schug
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany
| | - Alexander Bartel
- Institute for Veterinary Epidemiology and Biostatistics, Department of Veterinary Medicine, Freie Universität Berlin, Germany
| | - Marita Meurer
- Department of Physiological Chemistry, and Research Center for Emerging Infections and Zoonoses (RIZ), University of Veterinary Medicine Hannover, Foundation, Germany
| | - Anissa D Scholtzek
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany
| | - Julian Brombach
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany
| | - Vivian Hensel
- Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut (FLI), Neustadt-Mariensee, Germany
| | - Séamus Fanning
- UCD-Centre for Food Safety, School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland
| | - Stefan Schwarz
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany
| | - Andrea T Feßler
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany.
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Ou F, McGoverin C, Swift S, Vanholsbeeck F. Near real-time enumeration of live and dead bacteria using a fibre-based spectroscopic device. Sci Rep 2019; 9:4807. [PMID: 30886183 PMCID: PMC6423134 DOI: 10.1038/s41598-019-41221-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 02/28/2019] [Indexed: 01/05/2023] Open
Abstract
A rapid, cost-effective and easy method that allows on-site determination of the concentration of live and dead bacterial cells using a fibre-based spectroscopic device (the optrode system) is proposed and demonstrated. Identification of live and dead bacteria was achieved by using the commercially available dyes SYTO 9 and propidium iodide, and fluorescence spectra were measured by the optrode. Three spectral processing methods were evaluated for their effectiveness in predicting the original bacterial concentration in the samples: principal components regression (PCR), partial least squares regression (PLSR) and support vector regression (SVR). Without any sample pre-concentration, PCR achieved the most reliable results. It was able to quantify live bacteria from 108 down to 106.2 bacteria/mL and showed the potential to detect as low as 105.7 bacteria/mL. Meanwhile, enumeration of dead bacteria using PCR was achieved between 108 and 107 bacteria/mL. The general procedures described in this article can be applied or modified for the enumeration of bacteria within populations stained with fluorescent dyes. The optrode is a promising device for the enumeration of live and dead bacterial populations particularly where rapid, on-site measurement and analysis is required.
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Affiliation(s)
- Fang Ou
- Department of Physics, The University of Auckland, Auckland, New Zealand.
- The Dodd-Walls Centre for Photonic and Quantum Technologies, Auckland, New Zealand.
| | - Cushla McGoverin
- Department of Physics, The University of Auckland, Auckland, New Zealand
- The Dodd-Walls Centre for Photonic and Quantum Technologies, Auckland, New Zealand
| | - Simon Swift
- School of Medical Sciences, The University of Auckland, Auckland, New Zealand
| | - Frédérique Vanholsbeeck
- Department of Physics, The University of Auckland, Auckland, New Zealand
- The Dodd-Walls Centre for Photonic and Quantum Technologies, Auckland, New Zealand
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3
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Venturelli OS, Carr AC, Fisher G, Hsu RH, Lau R, Bowen BP, Hromada S, Northen T, Arkin AP. Deciphering microbial interactions in synthetic human gut microbiome communities. Mol Syst Biol 2018; 14:e8157. [PMID: 29930200 PMCID: PMC6011841 DOI: 10.15252/msb.20178157] [Citation(s) in RCA: 241] [Impact Index Per Article: 40.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Revised: 05/13/2018] [Accepted: 05/22/2018] [Indexed: 12/19/2022] Open
Abstract
The ecological forces that govern the assembly and stability of the human gut microbiota remain unresolved. We developed a generalizable model-guided framework to predict higher-dimensional consortia from time-resolved measurements of lower-order assemblages. This method was employed to decipher microbial interactions in a diverse human gut microbiome synthetic community. We show that pairwise interactions are major drivers of multi-species community dynamics, as opposed to higher-order interactions. The inferred ecological network exhibits a high proportion of negative and frequent positive interactions. Ecological drivers and responsive recipient species were discovered in the network. Our model demonstrated that a prevalent positive and negative interaction topology enables robust coexistence by implementing a negative feedback loop that balances disparities in monospecies fitness levels. We show that negative interactions could generate history-dependent responses of initial species proportions that frequently do not originate from bistability. Measurements of extracellular metabolites illuminated the metabolic capabilities of monospecies and potential molecular basis of microbial interactions. In sum, these methods defined the ecological roles of major human-associated intestinal species and illuminated design principles of microbial communities.
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Affiliation(s)
| | - Alex C Carr
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Garth Fisher
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Ryan H Hsu
- California Institute for Quantitative Biosciences, University of California Berkeley, Berkeley, CA, USA
| | - Rebecca Lau
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Benjamin P Bowen
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Susan Hromada
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
| | - Trent Northen
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Adam P Arkin
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- California Institute for Quantitative Biosciences, University of California Berkeley, Berkeley, CA, USA
- Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA
- Energy Biosciences Institute, University of California Berkeley, Berkeley, CA, USA
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4
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Ou F, McGoverin C, Swift S, Vanholsbeeck F. Absolute bacterial cell enumeration using flow cytometry. J Appl Microbiol 2017; 123:464-477. [DOI: 10.1111/jam.13508] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 05/18/2017] [Accepted: 06/04/2017] [Indexed: 11/29/2022]
Affiliation(s)
- F. Ou
- Department of Physics; The Dodd-Walls Centre for Photonic and Quantum Technologies; The University of Auckland; Auckland New Zealand
| | - C. McGoverin
- Department of Physics; The Dodd-Walls Centre for Photonic and Quantum Technologies; The University of Auckland; Auckland New Zealand
| | - S. Swift
- School of Medical Sciences; The University of Auckland; Auckland New Zealand
| | - F. Vanholsbeeck
- Department of Physics; The Dodd-Walls Centre for Photonic and Quantum Technologies; The University of Auckland; Auckland New Zealand
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5
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Pina-Vaz C, Costa-de-Oliveira S, Silva-Dias A, Silva AP, Teixeira-Santos R, Rodrigues AG. Flow Cytometry in Microbiology: The Reason and the Need. ACTA ACUST UNITED AC 2017. [DOI: 10.1007/978-981-10-4499-1_7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
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6
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PRISE2: software for designing sequence-selective PCR primers and probes. BMC Bioinformatics 2014; 15:317. [PMID: 25252611 PMCID: PMC4261892 DOI: 10.1186/1471-2105-15-317] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 09/20/2014] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND PRISE2 is a new software tool for designing sequence-selective PCR primers and probes. To achieve high level of selectivity, PRISE2 allows the user to specify a collection of target sequences that the primers are supposed to amplify, as well as non-target sequences that should not be amplified. The program emphasizes primer selectivity on the 3' end, which is crucial for selective amplification of conserved sequences such as rRNA genes. In PRISE2, users can specify desired properties of primers, including length, GC content, and others. They can interactively manipulate the list of candidate primers, to choose primer pairs that are best suited for their needs. A similar process is used to add probes to selected primer pairs. More advanced features include, for example, the capability to define a custom mismatch penalty function. PRISE2 is equipped with a graphical, user-friendly interface, and it runs on Windows, Macintosh or Linux machines. RESULTS PRISE2 has been tested on two very similar strains of the fungus Dactylella oviparasitica, and it was able to create highly selective primers and probes for each of them, demonstrating the ability to create useful sequence-selective assays. CONCLUSIONS PRISE2 is a user-friendly, interactive software package that can be used to design high-quality selective primers for PCR experiments. In addition to choosing primers, users have an option to add a probe to any selected primer pair, enabling design of Taqman and other primer-probe based assays. PRISE2 can also be used to design probes for FISH and other hybridization-based assays.
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7
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Jernberg C, Jansson JK. Impact of 4-chlorophenol contamination and/or inoculation with the 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L, on soil bacterial community structure. FEMS Microbiol Ecol 2009; 42:387-97. [PMID: 19709298 DOI: 10.1111/j.1574-6941.2002.tb01028.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L (chromosomally tagged with the firefly luciferase gene, luc) was inoculated into 4-chlorophenol-contaminated soil to assess the impact of bioaugmentation with a biodegrading strain on the indigenous microbiota. Simultaneously, the impact of 4-chlorophenol alone, or inoculation with A. chlorophenolicus into non-contaminated soil, was addressed. Using terminal restriction fragment length polymorphism (T-RFLP) several significant changes were detected in community fingerprint patterns obtained from soil microcosms treated under the different conditions. The relative abundances of some populations, as judged by the relative intensity of terminal restriction fragments, were significantly impacted by either 4-chlorophenol, A. chlorophenolicus inoculation, or by a combination of both inoculation and 4-chlorophenol contamination. Some populations were significantly stimulated and others were significantly repressed when compared to control soil with no additions. For several peaks, the positive or negative impact imposed by the treatments increased over the 13-day incubation period. Some members of the bacterial community were specifically sensitive to A. chlorophenolicus inoculation or to 4-chlorophenol contamination, whereas other populations remained relatively unaffected by any of the treatments. The A. chlorophenolicus inoculum was also monitored by T-RFLP and was found to have a significantly higher relative abundance in soil contaminated with 4-chlorophenol. These results were substantiated by a high correlation to luciferase activity measurements and the number of colony forming units of the inoculum. Therefore, the A. chlorophenolicus A6L population was positively stimulated by the presence of the 4-chlorophenol substrate (180 microg g(-1) soil) that it catabolized during the first 8 days of the incubation period as a carbon and energy source. Together, these results demonstrate that specific populations in the soil bacterial community rapidly fluctuated in response to specific disturbances and the resulting shifts in the community may therefore represent an adjustment in community structure favoring those populations best capable of responding to novel stress scenarios.
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Affiliation(s)
- Cecilia Jernberg
- Södertörn University College, Section for Natural Sciences, P.O. Box 4101, S-141 04 Huddinge, Sweden
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8
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Kilpi MK, Atosuo JT, Lilius EME. Bacteriolytic activity of the alternative pathway of complement differs kinetically from the classical pathway. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2009; 33:1102-1110. [PMID: 19527746 DOI: 10.1016/j.dci.2009.06.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 06/05/2009] [Accepted: 06/06/2009] [Indexed: 05/27/2023]
Abstract
The interaction between bacterial cells and activated complement components as a kinetic biological event is described. The bacteriolytic activity of complement in human and fish serum was assayed by measuring the decrease of bioluminescence of Escherichia coli transformed with lux genes. From the kinetic curves, the bacteriolytic CB(50)- and AB(50)-units were derived at any desired time point. It was observed that these values were irregular but decreased as a function of incubation time, and reached equal values during prolonged incubation, suggesting that the difference between the classical and alternative pathway activity is kinetic. From the kinetic curves, entirely new parameters could be derived: rate of the activation phase, rate of killing by the lytic phase and rate of killing by the entire pathway in undiluted serum. The rates of human and fish classical pathway were about five and two times higher than those of the alternative pathway respectively.
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Affiliation(s)
- Maaria K Kilpi
- Department of Biochemistry and Food Chemistry, University of Turku, 20014 Turku, Finland.
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9
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Urgun-Demirtas M, Stark B, Pagilla K. Use of Genetically Engineered Microorganisms (GEMs) for the Bioremediation of Contaminants. Crit Rev Biotechnol 2008; 26:145-64. [PMID: 16923532 DOI: 10.1080/07388550600842794] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
This paper presents a critical review of the literature on the application of genetically engineered microorganisms (GEMs) in bioremediation. The important aspects of using GEMs in bioremediation, such as development of novel strains with desirable properties through pathway construction and the modification of enzyme specificity and affinity, are discussed in detail. Particular attention is given to the genetic engineering of bacteria using bacterial hemoglobin (VHb) for the treatment of aromatic organic compounds under hypoxic conditions. The application of VHb technology may advance treatment of contaminated sites, where oxygen availability limits the growth of aerobic bioremediating bacteria, as well as the functioning of oxygenases required for mineralization of many organic pollutants. Despite the many advantages of GEMs, there are still concerns that their introduction into polluted sites to enhance bioremediation may have adverse environmental effects, such as gene transfer. The extent of horizontal gene transfer from GEMs in the environment, compared to that of native organisms including benefits regarding bacterial bioremediation that may occur as a result of such transfer, is discussed. Recent advances in tracking methods and containment strategies for GEMs, including several biological systems that have been developed to detect the fate of GEMs in the environment, are also summarized in this review. Critical research questions pertaining to the development and implementation of GEMs for enhanced bioremediation have been identified and posed for possible future research.
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Affiliation(s)
- Meltem Urgun-Demirtas
- Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, 60616, USA
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10
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Fu Q, Ruegger P, Bent E, Chrobak M, Borneman J. PRISE (PRImer SElector): software for designing sequence-selective PCR primers. J Microbiol Methods 2007; 72:263-7. [PMID: 18221808 DOI: 10.1016/j.mimet.2007.12.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Revised: 12/16/2007] [Accepted: 12/16/2007] [Indexed: 11/19/2022]
Abstract
This report presents PRImer Selector (PRISE), a new software package that implements several features that improve and streamline the design of sequence-selective PCR primers. The PRISE design process involves two main steps. In the first step, target and non-target DNA sequences are identified. In the second step, primers are designed to amplify target (but not non-target) sequences. One important feature of PRISE is that it automates the task of placing primer-template mismatches at the 3' end of the primers - a property that is crucial for sequence selectivity. Once a list of candidate primers has been produced, sorting tools in PRISE speed up the selection process by allowing a user to sort the primers by properties such as amplicon length, GC content and sequence selectivity. PRISE can be used to design primers with a range of specificities, targeting individual sequences as well as diverse assemblages of genes. PRISE also allows user-defined primers to be analyzed, enabling their properties to be examined in relation to target and non-target sequences. The utility of PRISE was demonstrated by using it to design sequence-selective PCR primers for an rRNA gene from the fungus Pochonia chlamydosporia.
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Affiliation(s)
- Qi Fu
- Department of Plant Pathology, University of California, Riverside, CA 92521, USA
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11
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Joung YH, Kim HR, Lee MK, Park AJ. Fluconazole susceptibility testing of Candida species by flow cytometry. J Infect 2006; 54:504-8. [PMID: 17084902 DOI: 10.1016/j.jinf.2006.09.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Revised: 09/05/2006] [Accepted: 09/15/2006] [Indexed: 11/17/2022]
Abstract
OBJECTIVE Currently, antifungal drug susceptibility testing is labor-intensive, limited by delays in obtaining results and high costs. The purpose of this study was to determine the usefulness of flow cytometry (FCM) antifungal drug susceptibility testing as a routine laboratory procedure. METHODS A total of 24 clinical isolates of Candida spp. and reference strains were tested for susceptibility to fluconazole by FCM using propidium iodide (PI) as an indicator of viability. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of fluconazole that resulted in an increase of 30% in mean channel fluorescence (MCF), compared to the growth control. FCM results were compared with MIC results as determined by the Clinical and Laboratory Standards Institute (CLSI) method. RESULTS An 8h incubation was sufficient for determination of the MICs. The results by FCM at 8h and the NCCLS methods at 24h showed 87.5% agreement to within two drug dilutions. However, the FCM method is labor-intensive in proportion to the larger number of samples. For Candida lusitaniae, MICs by the FCM method showed poor correlation with the CLSI method. CONCLUSIONS Further evaluation is necessary to assess the usefulness of FCM as a technique for routine antifungal MIC testing in the clinical laboratory.
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Affiliation(s)
- Young Hee Joung
- Department of Laboratory Medicine, Chung-Ang University College of Medicine, 65-207, 3-Ka Hangang-Ro, Yongsan-Ku, Seoul 140-757, South Korea
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Alkorta I, Epelde L, Mijangos I, Amezaga I, Garbisu C. Bioluminescent bacterial biosensors for the assessment of metal toxicity and bioavailability in soils. REVIEWS ON ENVIRONMENTAL HEALTH 2006; 21:139-52. [PMID: 16898676 DOI: 10.1515/reveh.2006.21.2.139] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
A major factor governing the toxicity of heavy metals in soils is their bioavailability. Traditionally, sequential extraction procedures using different extractants followed by chemical analysis have been used for determining the biologically available fraction of metals in soils. Yet, the transfer of results obtained on non-biological systems to biological ones is certainly questionable. Therefore, bioluminescence-based bacterial biosensors have been developed using genetically engineered microorganisms, constructed by fusing transcriptionally active components of metal resistance mechanisms to lux genes from naturally bioluminescent bacteria like Vibrio fischeri for the assessment of metal toxicity and bioavailability in polluted soils. As compared to chemical methods, bacterial biosensors present certain advantages, such as selectivity, sensitivity, simplicity, and low cost. Despite certain inherent limitations, bacterial bioluminescent systems have proven their usefulness in soils under laboratory and field conditions. Finally, green fluorescent protein-based bacterial biosensors are also applicable for determining with high sensitivity the bioavailability of heavy metals in soil samples.
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Affiliation(s)
- I Alkorta
- Biophysics Unit, University of the Basque Country, Bilbao, Spain
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13
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Lehtinen J, Virta M, Lilius EM. Fluoro-luminometric real-time measurement of bacterial viability and killing. J Microbiol Methods 2003; 55:173-86. [PMID: 14500009 DOI: 10.1016/s0167-7012(03)00134-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The viability and killing of Escherichia coli was measured on a real-time basis using a fluoro-luminometric device, which allows successive measurements of fluorescence and bioluminescence without user intervention. Bacteria were made fluorescent and bioluminescent by expression of gfp and insect luciferase (lucFF) genes. The green fluorescent protein (GFP) is a highly fluorescent, extremely stable protein, which accumulates in cells during growth, and therefore the measured fluorescence signal was proportional to the total number of cells. The luciferase reaction is dependent of ATP produced by living cells, so that the bioluminescence level was a direct measure of the viable cells. In contrast to the bacterial luciferase, the insect luciferase uses a water-soluble and nonvolatile substrate, which makes automated multi-well microplate assay possible. For the validation of the assay, the proportion of living and dead cell populations was experimentally modified by incubating E. coli cells in the presence of various ethanol concentrations. Bacterial viability and killing measured by a fluoro-luminometric assay correlated fairly well with the reference methods: conventional plate counting, optical density measurement and various flow cytometric analyses. The real-time assay described here allows following the changes in bacterial cultures and assessing the bactericidal and other effects of various chemical, immunological and physical agents simultaneously in large numbers of samples.
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Affiliation(s)
- Janne Lehtinen
- Department of Biochemistry and Food Chemistry, University of Turku, Arcanum, Vatselankatu 2, 20014, Turku, Finland.
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14
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Yanagita K, Manome A, Meng XY, Hanada S, Kanagawa T, Tsuchida T, Mackie RI, Kamagata Y. Flow cytometric sorting, phylogenetic analysis and in situ detection of Oscillospira guillermondii, a large, morphologically conspicuous but uncultured ruminal bacterium. Int J Syst Evol Microbiol 2003; 53:1609-1614. [PMID: 13130057 DOI: 10.1099/ijs.0.02541-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Flow cytometric sorting based on its large cell size enabled an enriched fraction of Oscillospira guillermondii cells to be obtained from the rumen contents of a sheep. Phylogenetic analysis based on cloned 16S rDNA sequences indicated that the bacterium is a member of the low-G+C Gram-positive bacterial cluster. Sporobacter termitidis and Papillibacter cinnamivorans were the most closely related known species, with sequence similarities of only 86.3-88.1 %. Fluorescently labelled 16S rRNA-targeted oligonucleotide probes specific for Oscillospira were designed and applied to the rumen sample from which the enriched fraction was obtained. The probes hybridized specifically with the large, morphologically conspicuous Oscillospira cells.
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Affiliation(s)
- Kazuhiro Yanagita
- Center Research Laboratories, Ajinomoto Co., Kawasaki 210-8681, Japan
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Akira Manome
- Center Research Laboratories, Ajinomoto Co., Kawasaki 210-8681, Japan
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Xian-Ying Meng
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Satoshi Hanada
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Takahiro Kanagawa
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Takayasu Tsuchida
- Center Research Laboratories, Ajinomoto Co., Kawasaki 210-8681, Japan
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
| | - Roderick I Mackie
- Department of Animal Sciences, University of Illinois Urbana-Champaign, Urbana IL 61801, USA
| | - Yoichi Kamagata
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan
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GUS and GFP transformation of the biocontrol strain Clonostachys rosea IK726 and the use of these marker genes in ecological studies. ACTA ACUST UNITED AC 2002. [DOI: 10.1017/s095375620200607x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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16
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Björklöf K, Jørgensen KS. Applicability of non-antibiotic resistance marker genes in ecological studies of introduced bacteria in forest soil. FEMS Microbiol Ecol 2001. [DOI: 10.1111/j.1574-6941.2001.tb00896.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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17
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Fould S, Dieng A, Davies K, Normand P, Mateille T. Immunological quantification of the nematode parasitic bacterium Pasteuria penetrans in soil. FEMS Microbiol Ecol 2001. [DOI: 10.1111/j.1574-6941.2001.tb00866.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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18
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Frahm E, Heiber I, Ludwig W, Obst U. Rapid parallel detection of hygienically relevant microorganisms in water samples by PCR and specific hybridization in microtiter plates. Syst Appl Microbiol 2001; 24:423-9. [PMID: 11822680 DOI: 10.1078/0723-2020-00056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A molecular biological test protocol for the parallel detection of enterococci and Pseudomonas aeruginosa in drinking water was developed. Amplicons labelled with digoxigenin during PCR were hybridized to specific 23S rDNA targeted oligonucleotide probes immobilized in microtiter plates. Detection was performed by addition of anti-digoxigenin-peroxidase-conjugate and chromogenic substrate. Specificity of the probes was evaluated by using pure cultures. First evaluation data with natural water samples in comparison to conventional microbiological analysis according to the German Drinking Water Regulation showed good agreement. Its feasible and rapid performance should be advantageous for use in routine drinking water quality control. Further comparative evaluation studies need to be undertaken to determine the true applicability for routine testing of water samples.
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Affiliation(s)
- E Frahm
- Forschungszentrum Karlsruhe GmbH, ITC-WGT, Abt. Umweltmikrobiologie, Germany
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19
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MacGregor BJ, Toze S, Alm EW, Sharp R, Ziemer CJ, Stahl DA. Distribution and abundance of Gram-positive bacteria in the environment: development of a group-specific probe. J Microbiol Methods 2001; 44:193-203. [PMID: 11240041 DOI: 10.1016/s0167-7012(00)00243-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We developed a 16S rRNA-targeted oligonucleotide probe (S-P-GPos-1200-a-A-13) for the Gram-positive bacteria, confirmed its specificity by database searches and hybridization studies, and investigated the effects of humic acids on membrane hybridizations with this probe. S-P-GPos-1200-a-A-13 was used to estimate the abundance of Gram-positive populations in the bovine rumen and Lake Michigan sediments. This probe should be useful for studies of the environmental distribution of Gram-positive bacteria and the detection of uncultured, phylogenetically Gram-positive bacteria with variable or negative Gram staining reactions, and could serve for Gram staining in some diagnostic settings.
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Affiliation(s)
- B J MacGregor
- Civil Engineering Department, Northwestern University, Evanston, IL 60208, USA
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20
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Unge A, Jansson J. Monitoring Population Size, Activity, and Distribution of gfp-luxAB-Tagged Pseudomonas fluorescens SBW25 during Colonization of Wheat. MICROBIAL ECOLOGY 2001; 41:290-300. [PMID: 12032602 DOI: 10.1007/s002480000047] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2000] [Accepted: 05/03/2000] [Indexed: 05/23/2023]
Abstract
Increasingly, focus has been directed towards the use of microorganisms as biological control agents to combat fungal disease, as an alternative to chemical fungicides. Pseudomonas fluorescens SBW25 is one bacterial strain that has been demonstrated to promote plant growth by biocontrol of pathogenic fungi. To understand the mode of action of this bacterium, information regarding its localization and metabolic activity on plants is important. In this study, a gfp/luxAB-tagged derivative of P. fluorescens SBW25, expressing the green fluorescent protein (GFP) and bacterial luciferase, was monitored during colonization of wheat starting from seed inoculation. Since bacterial luciferase is dependent on cellular energy reserves for phenotypic expression, metabolically active cells were detected using this marker. In contrast, the stable GFP fluorescence phenotype was used to detect the cells independently of their metabolic status. The combination of these two markers enabled P. fluorescens SBW25 cells to be monitored on wheat plants to determine their specific location and metabolic activity. Studies on homogenized wheat plant parts demonstrated that the seed was the preferred location of P. fluorescens SBW25 during the 65-day time period studied, but the leaves and roots were also colonized. Interestingly, the bacteria were also found to be metabolically active on all plant parts examined. In situ localization of P. fluorescens SBW25 using a combination of different microscopic techniques confirmed the preference for the cells to colonize specific regions of the seed. We speculate that the colonization pattern of P. fluorescens SBW25 can be linked to the mechanism of protection of plants from fungal infection.
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Affiliation(s)
- A. Unge
- Department of Biochemistry, Stockholm University, S-10691 Stockholm, Sweden
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21
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Elväng AM, Westerberg K, Jernberg C, Jansson JK. Use of green fluorescent protein and luciferase biomarkers to monitor survival and activity of Arthrobacter chlorophenolicus A6 cells during degradation of 4-chlorophenol in soil. Environ Microbiol 2001; 3:32-42. [PMID: 11225721 DOI: 10.1046/j.1462-2920.2001.00156.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The recently isolated novel species Arthrobacter chlorophenolicus A6 is capable of growth on and degradation of high concentrations of 4-chlorophenol (up to 350 microg ml(-1)) as the sole carbon and energy source. This strain shows promise for bioremediation of environmental sites contaminated with high levels of chlorophenols. In this study, green fluorescent protein (gfp) or luciferase (luc) genes were used as biomarkers for monitoring cell number and activity, respectively, during degradation of 4-chlorophenol by A. chlorophenolicus cells. The individual marked strains, Arthrobacter chlorophenolicus A6L (luc-tagged) and Arthrobacter chlorophenolicus A6G (gfp-tagged), were monitored during degradation of 250 microg ml(-1) 4-chlorophenol in pure culture and 175 microg g(-1) 4-chlorophenol in soil microcosms. Both gene-tagged strains were capable of cleaning up the contaminated soil during 9 d incubation. During the bioremediation experiments, the luc-tagged cells were monitored using luminometry and the gfp-tagged cells using flow cytometry, in addition to selective plate counting for both strains. The cells remained at high population levels in the soil (evidenced by GFP-fluorescent cell counts) and the A. chlorophenolicus A6L population was metabolically active (evidenced by luciferase activity measurements). These results demonstrate that the Arthrobacter chlorophenolicus A6 inoculum is effective for cleaning-up soil containing high concentrations of 4-chlorophenol.
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Affiliation(s)
- A M Elväng
- Department of Biochemistry, Arrhenius Laboratories, Stockholm University, Sweden
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22
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Bakermans C, Madsen EL. Use of substrate responsive-direct viable counts to visualize naphthalene degrading bacteria in a coal tar-contaminated groundwater microbial community. J Microbiol Methods 2000; 43:81-90. [PMID: 11121606 DOI: 10.1016/s0167-7012(00)00210-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A microscopy-based method was developed to distinguish naphthalene-degrading bacteria within the microbial community of a coal tar-contaminated groundwater system. Pure cultures of Pseudomonas putida NCIB 9816-4 were used to develop the substrate responsive-direct viable count (SR-DVC) method. Cells were concentrated on membrane filters, placed on agar plates of Stanier's minimal basal salts media containing antibiotics (nalidixic acid, piromidic acid, pipemidic acid, and cephalexin), and exposed to vapors of naphthalene. Following brief incubation, samples were fixed in 2% formaldehyde and examined by epifluorescent microscopy. Pure cultures displayed the expected cell elongation response to the SR-DVC assay and required a minimum incubation time of 9 h for differentiation of elongated cells. When applied to groundwater samples from the study site, naphthalene responsive cells in the groundwater community were easily distinguished from unresponsive cells and debris (350+/-180 substrate responsive cells/ml, relative to negative controls with no added growth substrate). In an attempt to reduce background counts of elongated bacteria and fungi, the SR-DVC procedure was modified by adding a wash step prior to incubation and a fungal inhibitor, cyclohexamide, to the plates. When groundwater samples were subjected to the modified procedure, only cells in washed samples showed a significant response to naphthalene (150+/-25 cells/ml), indicating the presence of inhibitory substances in the groundwater. Variations in response of the groundwater microbial community to the two SR-DVC procedures suggest that subsurface conditions (microbial and chemical composition) vary temporally. SR-DVC allows the phenotypes of individual naturally occurring cells to be assessed.
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Affiliation(s)
- C Bakermans
- Department of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA
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23
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Abstract
Biofilms are complex communities of microorganisms attached to surfaces or associated with interfaces. Despite the focus of modern microbiology research on pure culture, planktonic (free-swimming) bacteria, it is now widely recognized that most bacteria found in natural, clinical, and industrial settings persist in association with surfaces. Furthermore, these microbial communities are often composed of multiple species that interact with each other and their environment. The determination of biofilm architecture, particularly the spatial arrangement of microcolonies (clusters of cells) relative to one another, has profound implications for the function of these complex communities. Numerous new experimental approaches and methodologies have been developed in order to explore metabolic interactions, phylogenetic groupings, and competition among members of the biofilm. To complement this broad view of biofilm ecology, individual organisms have been studied using molecular genetics in order to identify the genes required for biofilm development and to dissect the regulatory pathways that control the plankton-to-biofilm transition. These molecular genetic studies have led to the emergence of the concept of biofilm formation as a novel system for the study of bacterial development. The recent explosion in the field of biofilm research has led to exciting progress in the development of new technologies for studying these communities, advanced our understanding of the ecological significance of surface-attached bacteria, and provided new insights into the molecular genetic basis of biofilm development.
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Affiliation(s)
- M E Davey
- Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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24
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Lowder M, Unge A, Maraha N, Jansson JK, Swiggett J, Oliver JD. Effect of starvation and the viable-but-nonculturable state on green fluorescent protein (GFP) fluorescence in GFP-tagged Pseudomonas fluorescens A506. Appl Environ Microbiol 2000; 66:3160-5. [PMID: 10919764 PMCID: PMC92128 DOI: 10.1128/aem.66.8.3160-3165.2000] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The green fluorescent protein (GFP) gene, gfp, of the jellyfish Aequorea victoria is being used as a reporter system for gene expression and as a marker for tracking prokaryotes and eukaryotes. Cells that have been genetically altered with the gfp gene produce a protein that fluoresces when it is excited by UV light. This unique phenotype allows gfp-tagged cells to be specifically monitored by nondestructive means. In this study we determined whether a gfp-tagged strain of Pseudomonas fluorescens continued to fluoresce under conditions under which the cells were starved, viable but nonculturable (VBNC), or dead. Epifluorescent microscopy, flow cytometry, and spectrofluorometry were used to measure fluorescence intensity in starved, VBNC, and dead or dying cells. Results obtained by using flow cytometry indicated that microcosms containing VBNC cells, which were obtained by incubation under stress conditions (starvation at 37.5 degrees C), fluoresced at an intensity that was at least 80% of the intensity of nonstressed cultures. Similarly, microcosms containing starved cells incubated at 5 and 30 degrees C had fluorescence intensities that were 90 to 110% of the intensity of nonstressed cells. VBNC cells remained fluorescent during the entire 6-month incubation period. In addition, cells starved at 5 or 30 degrees C remained fluorescent for at least 11 months. Treatment of the cells with UV light or incubation at 39 or 50 degrees C resulted in a loss of GFP from the cells. There was a strong correlation between cell death and leakage of GFP from the cells, although the extent of leakage varied depending on the treatment. Most dead cells were not GFP fluorescent, but a small proportion of the dead cells retained some GFP at a lower concentration than the concentration in live cells. Our results suggest that gfp-tagged cells remain fluorescent following starvation and entry into the VBNC state but that fluorescence is lost when the cells die, presumably because membrane integrity is lost.
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Affiliation(s)
- M Lowder
- Department of Biology, University of North Carolina at Charlotte, 28223, USA
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25
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Abstract
Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.
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26
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Alvarez-Barrientos A, Arroyo J, Cantón R, Nombela C, Sánchez-Pérez M. Applications of flow cytometry to clinical microbiology. Clin Microbiol Rev 2000; 13:167-95. [PMID: 10755996 PMCID: PMC100149 DOI: 10.1128/cmr.13.2.167] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.
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Affiliation(s)
- A Alvarez-Barrientos
- Departamento de Microbiología II, Facultad de Farmacia, Universidad Complutense de Madrid, Spain
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27
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Quantification de bactéries nitrifiantes du genre Nitrobacter en milieux aquatiques (l'estuaire de la Seine, France). ACTA ACUST UNITED AC 1999. [DOI: 10.1016/s0764-4469(99)80102-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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28
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Errampalli D, Leung K, Cassidy MB, Kostrzynska M, Blears M, Lee H, Trevors JT. Applications of the green fluorescent protein as a molecular marker in environmental microorganisms. J Microbiol Methods 1999; 35:187-99. [PMID: 10333070 DOI: 10.1016/s0167-7012(99)00024-x] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
In this review, we examine numerous applications of the green fluorescent protein (GFP) marker gene in environmental microbiology research. The GFP and its variants are reviewed and applications in plant-microbe interactions, biofilms, biodegradation, bacterial-protozoan interactions, gene transfer, and biosensors are discussed. Methods for detecting GFP-marked cells are also examined. The GFP is a useful marker in environmental microorganisms, allowing new research that will increase our understanding of microorganisms in the environment.
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Affiliation(s)
- D Errampalli
- Agriculture and Agri-Food Canada, Charlottetown, PEI
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29
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Unge A, Tombolini R, Molbak L, Jansson JK. Simultaneous monitoring of cell number and metabolic activity of specific bacterial populations with a dual gfp-luxAB marker system. Appl Environ Microbiol 1999; 65:813-21. [PMID: 9925621 PMCID: PMC91100 DOI: 10.1128/aem.65.2.813-821.1999] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A dual marker system was developed for simultaneous quantification of bacterial cell numbers and their activity with the luxAB and gfp genes, encoding bacterial luciferase and green fluorescent protein (GFP), respectively. The bioluminescence phenotype of the luxAB biomarker is dependent on cellular energy status. Since cellular metabolism requires energy, bioluminescence output is directly related to the metabolic activity of the cells. By contrast, GFP fluorescence has no energy requirement. Therefore, by combining these two biomarkers, total cell number and metabolic activity of a specific marked cell population could be monitored simultaneously. Two different bacterial strains, Escherichia coli DH5alpha and Pseudomonas fluorescens SBW25, were chromosomally tagged with the dual marker cassette, and the cells were monitored under different conditions by flow cytometry, plate counting, and luminometry. During log-phase growth, the luciferase activity was proportional to the number of GFP-fluorescent cells and culturable cells. Upon entrance into stationary phase or during starvation, luciferase activity decreased due to a decrease in cellular metabolic activity of the population, but the number of GFP-fluorescing cells and culturable cells remained relatively stable. In addition, we optimized a procedure for extraction of bacterial cells from soil, allowing GFP-tagged bacteria in soil samples to be quantitated by flow cytometry. After 30 days of incubation of P. fluorescens SBW25::gfp/lux in soil, the cells were still maintained at high population densities, as determined by GFP fluorescence, but there was a slow decline in luciferase activity, implicating nutrient limitation. In conclusion, the dual marker system allowed simultaneous monitoring of the metabolic activity and cell number of a specific bacterial population and is a promising tool for monitoring of specific bacteria in situ in environmental samples.
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Affiliation(s)
- A Unge
- Department of Biochemistry, Stockholm University, S-10691 Stockholm, Sweden
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