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Probiotics research in Galleria mellonella a
Gerwald Köhler a
Department of Biochemistry & Microbiology; Oklahoma State University Center for Health Sciences; Tulsa, OK USA Accepted author version posted online: 05 Feb 2015.
Click for updates To cite this article: Gerwald Köhler (2015) Probiotics research in Galleria mellonella, Virulence, 6:1, 3-5 To link to this article: http://dx.doi.org/10.1080/21505594.2014.998967
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
EDITORIAL Virulence 6:1, 3--5; January 2015; © 2015 Taylor & Francis Group, LLC
Probiotics research in Galleria mellonella €hler* Gerwald Ko Department of Biochemistry & Microbiology; Oklahoma State University Center for Health Sciences; Tulsa, OK USA
Downloaded by [University of Bristol] at 03:20 03 March 2015
Keywords: Candida albicans, Galleria mellonella, infection model, Lactobacillus, Probiotic Probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” In essence, this definition was first coined in 2001 by an international expert panel convened by the Food and Agriculture Organization of the United Nations (FAO) and the WHO.1 Validity and acceptance of the definition over the years is evidenced by the fact that only a minor grammatical correction was recommended in a recent expert panel meeting of the International Scientific Association for Probiotics and Prebiotics (ISAPP).2 Clear definitions of probiotics are crucial for scientific research on probiotics, for producers and consumers of probiotic products, and for regulators who want to ensure product safety and protect the consumer from false or exaggerated health claims. Rigorous scientific research is necessary to prove or disprove that particular strains or groups of microorganisms confer health benefits to the host. The most recent recommendations on probiotics state that certain genera and species exert beneficial effects that can be considered probiotic.2 For example, genera-level effects include competitive exclusion of pathogens, butyrate and other short chain fatty acid (SCFA) production, or regulation of intestinal transit. Probiotic species might produce vitamins or beneficial enzymes, metabolize bile salt, exhibit antagonisms toward specific pathogens, neutralize toxic chemicals or carcinogens, and support barrier function of the intestinal epithelium. Far reaching immunological, endocrinological, and neurological effects, however, are usually associated with specific strains of probiotics that are equipped with genetic traits that are not present in other members of the species. It remains to be determined whether the
core benefits of probiotic genera/species are harbored in a “probiotic core genome” while strain-level probiotic mechanisms are encoded in highly specialized gene sets. At present, undefined microbial consortia (e.g. fecal microbiota transplants3,4) that exert beneficial effects on the host are not considered probiotics according to the latest expert panel report2. However, increased scrutiny of human or animal microbiota most likely will lead to identification of novel probiotics that are not members of the traditional genera with beneficial properties such as Lactobacillus or Bifidobacterium. For example, Faecalibacterium prausnitzi5,6 and Akkermansia muciniphila7,8 are considered as candidate probiotic species because of their positive effects on intestinal health in humans, but safety and efficacy of these bacteria has to be demonstrated through rigorous scientific research and randomized controlled trials. Consequently, selection and testing of microorganisms for potential use as probiotics in humans or animals is no easy task. In 2001 and 2002, expert consultations led to formulation of the FAO/ WHO Guidelines for the assessment of probiotics in food.1,9 These guidelines are still helpful today for selecting and evaluating probiotics as food, food supplement, or as probiotic drug for treatment and prevention of certain diseases.2,10,11 While evaluation of safety and efficacy with suitable methods is paramount, appropriate viability and shelf-life are, by definition, prerequisites for probiotics. Ultimately, efficacy and safety have to be confirmed in the intended target organism, i.e. for human probiotics through well-conducted clinical studies in humans. In vitro studies of probiotic candidates or studies in model organisms can only provide an initial motivation for health claims, but no
proof. Nevertheless, such research is a valid starting point and could give insights into potential mechanisms of probiotic action. Tests for tolerance to gastric acidity, resistance to bile, adherence ability to mucus and/or intestinal cells, and antimicrobial activities were suggested as in vitro studies by probiotics expert panels.1,9 Many researchers have adopted these approaches to screen for potentially probiotic strains. In vivo studies using rodents, zebrafish (Danio rerio), or invertebrates such as Caenorhabditis elegans and Drosophila melanogaster as animal models are certainly better suited to deliver relevant information on probiotic mechanisms. For example, some of the most exciting research on the microbiota-gut-brain axis and potential manipulation of cognitive functions by probiotics has been conducted in mice.12,13 The zebrafish model revealed the enhancement of fecundity and bone development by probiotic administration.14,15 C. elegans has emerged as versatile model for the study of pathogens, commensals, and probiotics. 16-19 Interestingly, symbiotic lactobacilli appear to be involved in metazoan intestinal development and stem cell proliferation, as recently reported in the fruit fly by Jones et al.20 In this issue of Virulence, Vilela and coworkers21 add another invertebrate model system to the probiotic researchers’ tool box: the wax moth Galleria mellonella. While G. mellonella is not (yet) as genetically tractable as D. melanogaster or C. elegans, simplicity of manipulation and infection of G. mellonella larvae combined with their survival at 25 and 37 C, make the wax moth an attractive model system.22 Especially in research on bacterial23,24 and fungal17,25-29 pathogenesis, G. mellonella larvae have shown great
*Correspondence to: Gerwald K€ ohler; Email: [email protected] Submitted: 12/10/2014; Accepted: 12/12/2014 http://dx.doi.org/10.1080/21505594.2014.998967
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promise as infection model. In their study, Vilela et al. utilized the larvae as model for infection with the pathogenic yeast Candida albicans and co-infection with a beneficial Lactobacillus acidophilus strain.21 Experimental candidiasis is well established in G. mellonella30-32 and thus an attempt to ameliorate the lethal outcome of the fungal infection by administration of the probiotics is a logical approach to test for probiotic interference with C. albicans pathogenicity. The authors initiated their study by demonstrating anti-Candida effects of the lactobacilli in vitro, i.e., inhibition of fungal filamentation and biofilm formation. Vigorous production of lactic acid by lactobacilli has already been shown to exert antagonistic effects on filamentation and C. albicans cell viability, especially under unbuffered low pH conditions, despite the relatively high acid tolerance of these fungi.33 Additional inhibitory substances produced by the lactobacilli might exacerbate these effects. Vilela et al developed an inoculation
protocol for co-infection and confirmed that the lactobacilli were not pathogenic for the G. mellonella larvae. Subsequently, co-infection experiments revealed that the L. acidophilus strain indeed was able to reduce fungal burden in the larvae and lethality of the infection. The model system also allowed the researchers to perform histological analyses to characterize the effects of the beneficial bacteria on the fungal growth patterns in vivo. The work offers a first proof of concept, but many questions about the probiotic mechanisms encountered in this model remain open. How do the lactobacilli suppress C. albicans in the larvae? What is the role of the insect immune system? Are the findings relevant to probiotic research in humans? In summary, a new invertebrate model to elucidate some aspects of probiotic interference with microbial pathogens has been introduced. The model system has clear advantages such as ease of use and reduced costs, especially in comparison to vertebrate models22. In contrast to
D. melanogaster and C. elegans, pathogenic mechanisms of fungal or bacterial infections and host immune defense mechanisms in G. mellonella appear to correlate more closely with those encountered in humans.22 Conversely, the lack of a complete genome sequence, the absence of reporter and mutant strains, and the need for standardization across different sources and laboratories,22,34 currently dampen the enthusiasm for the G. mellonella model; although future progress is likely to improve upon these drawbacks. In conclusion, G. mellonella has merit as a new model for foundational research on probiotics, but it will certainly not replace the randomized controlled trials in humans so urgently needed to evaluate efficacy of many so-called “probiotics."
References
8. Tilg H, Moschen AR. Microbiota and diabetes: an evolving relationship. Gut 2014; 63:1513-21; PMID:24833634; http://dx.doi.org/10.1136/gutjnl2014-306928 9. Food and Agricultural Organization of the United Nations and World Health Organization. Report of a joint FAO/WHO working group on drafting guidelines for the evaluation of probiotics in food. Food and Agricultural Organization of the United Nations; online, ftp://ftp.fao.org/es/esn/food/wgreport2.pdf. 2002. 10. Reid G, Food, Agricultural Organization of the United N, the WHO. The importance of guidelines in the development and application of probiotics. Curr Pharm Design 2005; 11:11-6; PMID:15638748; http://dx.doi.org/10.2174/1381612053382395 11. Reid G, Kim SO, Kohler GA. Selecting, testing and understanding probiotic microorganisms. FEMS Immunol Med Microbiol 2006; 46:149-57; PMID:16487295; http://dx.doi.org/10.1111/j.1574695X.2005.00026.x 12. Bravo JA, Forsythe P, Chew MV, Escaravage E, Savignac HM, Dinan TG, Bienenstock J, Cryan JF. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci U S A 2011; 108:16050-5; PMID:21876150; http://dx.doi. org/10.1073/pnas.1102999108 13. Gareau MG. Microbiota-gut-brain axis and cognitive function. Adv Exp Med Biol 2014; 817:357-71; PMID:24997042; http://dx.doi.org/10.1007/978-14939-0897-4_16 14. Gioacchini G, Maradonna F, Lombardo F, Bizzaro D, Olivotto I, Carnevali O. Increase of fecundity by probiotic administration in zebrafish (Danio rerio). Reproduction (Cambridge, England) 2010; 140:953-9; PMID:20833753; http://dx.doi.org/10.1530/REP-100145 15. Maradonna F, Gioacchini G, Falcinelli S, Bertotto D, Radaelli G, Olivotto I, Carnevali O. Probiotic supplementation promotes calcification in Danio rerio larvae: a molecular study. PloS One 2013; 8:e83155;
PMID:24358259; http://dx.doi.org/10.1371/journal. pone.0083155 Clark LC, Hodgkin J. Commensals, probiotics and pathogens in the Caenorhabditis elegans model. Cell Microbiol 2014; 16:27-38; PMID:24168639; http:// dx.doi.org/10.1111/cmi.12234 Fuchs BB, Mylonakis E. Using non-mammalian hosts to study fungal virulence and host defense. Curr Opin Microbiol 2006; 9:346-51; PMID:16814595; http:// dx.doi.org/10.1016/j.mib.2006.06.004 Glavis-Bloom J, Muhammed M, Mylonakis E. Of model hosts and man: using Caenorhabditis elegans, Drosophila melanogaster and Galleria mellonella as model hosts for infectious disease research. Adv Exp Med Biol 2012; 710:11-7; PMID:22127881; http:// dx.doi.org/10.1007/978-1-4419-5638-5_2 Kim Y, Mylonakis E. Caenorhabditis elegans immune conditioning with the probiotic bacterium Lactobacillus acidophilus strain NCFM enhances gram-positive immune responses. Infect Immunity 2012; 80:2500-8; PMID:22585961; http://dx.doi.org/10.1128/ IAI.06350-11 Jones RM, Luo L, Ardita CS, Richardson AN, Kwon YM, Mercante JW, Alam A, Gates CL, Wu H, Swanson PA, et al. Symbiotic lactobacilli stimulate gut epithelial proliferation via Nox-mediated generation of reactive oxygen species. EMBO J 2013; 32:3017-28; PMID:24141879; http://dx.doi.org/10.1038/emboj. 2013.224 Vilela SF, Barbosa JO, Rossoni RD, Santos JD, Prata MC, Anbider AL, Jorge AO, Junqueira JC. Lactobacillus acidophilus ATCC 4356 inhibits biofilm formation by Candida albicans and attenuates the experimental candidiasis in Galleria mellonella. Virulence 2015; 6(1):29-39; PMID:25559739; http://dx.doi.org/ 10.4161/21505594.2014.981486 Nathan S. New to Galleria mellonella: modeling an ExPEC infection. Virulence 2014; 5:371-4; PMID: 24569500; http://dx.doi.org/10.4161/viru.28338 Ramarao N, Nielsen-Leroux C, Lereclus D. The insect Galleria mellonella as a powerful infection model to
1. Food and Agricultural Organization of the United Nations and World Health Organization. Health and nutritional properties of probiotics in food including powder milk with live lactic acid bacteria. World Health Organization; online, http://www.who.int/food safety/publications/fs_management/en/probiotics.pdf, 2001. 2. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, Morelli L, Canani RB, Flint HJ, Salminen S, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol 2014; 11:506-14; PMID:24912386; http://dx.doi.org/ 10.1038/nrgastro.2014.66 3. Smits LP, Bouter KE, de Vos WM, Borody TJ, Nieuwdorp M. Therapeutic potential of fecal microbiota transplantation. Gastroenterology 2013; 145:946-53; PMID:24018052; http://dx.doi.org/10.1053/j.gastro. 2013.08.058 4. van Nood E, Speelman P, Nieuwdorp M, Keller J. Fecal microbiota transplantation: facts and controversies. Curr Opin Gastroenterol 2014; 30:34-9; PMID:24241245; http://dx.doi.org/10.1097/MOG. 0000000000000024 5. Miquel S, Martin R, Bridonneau C, Robert V, Sokol H, Bermudez-Humaran LG, Thomas M, Langella P. Ecology and metabolism of the beneficial intestinal commensal bacterium Faecalibacterium prausnitzii. Gut Microbes 2014; 5:146-51; PMID:24637606; http://dx.doi.org/10.4161/gmic.27651 6. Miquel S, Martin R, Rossi O, Bermudez-Humaran LG, Chatel JM, Sokol H, Thomas M, Wells JM, Langella P. Faecalibacterium prausnitzii and human intestinal health. Curr Opin Microbiol 2013; 16:255-61; PMID:23831042; http://dx.doi.org/10.1016/j.mib. 2013.06.003 7. Joyce SA, Gahan CG. The gut microbiota and the metabolic health of the host. Curr Opin Gastroenterol 2014; 30:120-7; PMID:24468803; http://dx.doi.org/ 10.1097/MOG.0000000000000039
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Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
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mellonella from a subsequent lethal infection by Candida albicans and is mediated by the increased expression of antimicrobial peptides. Microb Infect / Institut Pasteur 2006; 8:2105-12; PMID:16782387; http://dx. doi.org/10.1016/j.micinf.2006.03.005 Fuchs BB, O’Brien E, Khoury JB, Mylonakis E. Methods for using Galleria mellonella as a model host to study fungal pathogenesis. Virulence 2010; 1:475-82; PMID: 21178491; http://dx.doi.org/10.4161/viru.1.6.12985 Fallon J, Kelly J, Kavanagh K. Galleria mellonella as a model for fungal pathogenicity testing. Methods Mol Biol (Clifton, NJ) 2012; 845:469-85; http://dx.doi. org/10.1007/978-1-61779-539-8_33 Brennan M, Thomas DY, Whiteway M, Kavanagh K. Correlation between virulence of Candida albicans mutants in mice and Galleria mellonella larvae. FEMS Immunol Med Microbiol 2002; 34:153-7; PMID:12381467; http://dx.doi.org/10.1111/j.1574695X.2002.tb00617.x Gago S, Garcia-Rodas R, Cuesta I, Mellado E, Alastruey-Izquierdo A. Candida parapsilosis, Candida
orthopsilosis, and Candida metapsilosis virulence in the non-conventional host Galleria mellonella. Virulence 2014; 5:278-85; PMID:24193303; http://dx.doi.org/ 10.4161/viru.26973 32. Junqueira JC. Models hosts for the study of oral candidiasis. Adv Exp Med Biol 2012; 710:95-105; PMID:22127889; http://dx.doi.org/10.1007/978-14419-5638-5_10 33. Kohler GA, Assefa S, Reid G. Probiotic interference of Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 with the opportunistic fungal pathogen Candida albicans. Infect Dis Obstetrics Gynecol 2012; 2012:636474; PMID:22811591; http://dx.doi.org/ 10.1155/2012/636474 34. Junqueira JC. Galleria mellonella as a model host for human pathogens: recent studies and new perspectives. Virulence 2012; 3:474-6; PMID:23211681; http://dx. doi.org/10.4161/viru.22493
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investigate bacterial pathogenesis. J Visualized Exp 2012:e4392; PMID:23271509 Mukherjee K, Raju R, Fischer R, Vilcinskas A. Galleria mellonella as a model host to study gut microbe homeostasis and brain infection by the human pathogen listeria monocytogenes. Adv Biochem Eng/Biotechnol 2013; 135:27-39; PMID:23708825; http://dx.doi. org/10.1007/10_2013_203 Bergin D, Brennan M, Kavanagh K. Fluctuations in haemocyte density and microbial load may be used as indicators of fungal pathogenicity in larvae of Galleria mellonella. Microb Infect / Institut Pasteur 2003; 5:1389-95; PMID:14670452; http://dx.doi.org/ 10.1016/j.micinf.2003.09.019 Dunphy GB, Oberholzer U, Whiteway M, Zakarian RJ, Boomer I. Virulence of Candida albicans mutants toward larval Galleria mellonella (Insecta, Lepidoptera, Galleridae). Canadian J Microbiol 2003; 49:514-24; PMID:14608387; http://dx.doi.org/10.1139/w03-064 Bergin D, Murphy L, Keenan J, Clynes M, Kavanagh K. Pre-exposure to yeast protects larvae of Galleria
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Virulence Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/kvir20
Probiotics research in Galleria mellonella a
Gerwald Köhler a
Department of Biochemistry & Microbiology; Oklahoma State University Center for Health Sciences; Tulsa, OK USA Accepted author version posted online: 05 Feb 2015.
Click for updates To cite this article: Gerwald Köhler (2015) Probiotics research in Galleria mellonella, Virulence, 6:1, 3-5 To link to this article: http://dx.doi.org/10.1080/21505594.2014.998967
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
EDITORIAL Virulence 6:1, 3--5; January 2015; © 2015 Taylor & Francis Group, LLC
Probiotics research in Galleria mellonella €hler* Gerwald Ko Department of Biochemistry & Microbiology; Oklahoma State University Center for Health Sciences; Tulsa, OK USA
Downloaded by [University of Bristol] at 03:20 03 March 2015
Keywords: Candida albicans, Galleria mellonella, infection model, Lactobacillus, Probiotic Probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” In essence, this definition was first coined in 2001 by an international expert panel convened by the Food and Agriculture Organization of the United Nations (FAO) and the WHO.1 Validity and acceptance of the definition over the years is evidenced by the fact that only a minor grammatical correction was recommended in a recent expert panel meeting of the International Scientific Association for Probiotics and Prebiotics (ISAPP).2 Clear definitions of probiotics are crucial for scientific research on probiotics, for producers and consumers of probiotic products, and for regulators who want to ensure product safety and protect the consumer from false or exaggerated health claims. Rigorous scientific research is necessary to prove or disprove that particular strains or groups of microorganisms confer health benefits to the host. The most recent recommendations on probiotics state that certain genera and species exert beneficial effects that can be considered probiotic.2 For example, genera-level effects include competitive exclusion of pathogens, butyrate and other short chain fatty acid (SCFA) production, or regulation of intestinal transit. Probiotic species might produce vitamins or beneficial enzymes, metabolize bile salt, exhibit antagonisms toward specific pathogens, neutralize toxic chemicals or carcinogens, and support barrier function of the intestinal epithelium. Far reaching immunological, endocrinological, and neurological effects, however, are usually associated with specific strains of probiotics that are equipped with genetic traits that are not present in other members of the species. It remains to be determined whether the
core benefits of probiotic genera/species are harbored in a “probiotic core genome” while strain-level probiotic mechanisms are encoded in highly specialized gene sets. At present, undefined microbial consortia (e.g. fecal microbiota transplants3,4) that exert beneficial effects on the host are not considered probiotics according to the latest expert panel report2. However, increased scrutiny of human or animal microbiota most likely will lead to identification of novel probiotics that are not members of the traditional genera with beneficial properties such as Lactobacillus or Bifidobacterium. For example, Faecalibacterium prausnitzi5,6 and Akkermansia muciniphila7,8 are considered as candidate probiotic species because of their positive effects on intestinal health in humans, but safety and efficacy of these bacteria has to be demonstrated through rigorous scientific research and randomized controlled trials. Consequently, selection and testing of microorganisms for potential use as probiotics in humans or animals is no easy task. In 2001 and 2002, expert consultations led to formulation of the FAO/ WHO Guidelines for the assessment of probiotics in food.1,9 These guidelines are still helpful today for selecting and evaluating probiotics as food, food supplement, or as probiotic drug for treatment and prevention of certain diseases.2,10,11 While evaluation of safety and efficacy with suitable methods is paramount, appropriate viability and shelf-life are, by definition, prerequisites for probiotics. Ultimately, efficacy and safety have to be confirmed in the intended target organism, i.e. for human probiotics through well-conducted clinical studies in humans. In vitro studies of probiotic candidates or studies in model organisms can only provide an initial motivation for health claims, but no
proof. Nevertheless, such research is a valid starting point and could give insights into potential mechanisms of probiotic action. Tests for tolerance to gastric acidity, resistance to bile, adherence ability to mucus and/or intestinal cells, and antimicrobial activities were suggested as in vitro studies by probiotics expert panels.1,9 Many researchers have adopted these approaches to screen for potentially probiotic strains. In vivo studies using rodents, zebrafish (Danio rerio), or invertebrates such as Caenorhabditis elegans and Drosophila melanogaster as animal models are certainly better suited to deliver relevant information on probiotic mechanisms. For example, some of the most exciting research on the microbiota-gut-brain axis and potential manipulation of cognitive functions by probiotics has been conducted in mice.12,13 The zebrafish model revealed the enhancement of fecundity and bone development by probiotic administration.14,15 C. elegans has emerged as versatile model for the study of pathogens, commensals, and probiotics. 16-19 Interestingly, symbiotic lactobacilli appear to be involved in metazoan intestinal development and stem cell proliferation, as recently reported in the fruit fly by Jones et al.20 In this issue of Virulence, Vilela and coworkers21 add another invertebrate model system to the probiotic researchers’ tool box: the wax moth Galleria mellonella. While G. mellonella is not (yet) as genetically tractable as D. melanogaster or C. elegans, simplicity of manipulation and infection of G. mellonella larvae combined with their survival at 25 and 37 C, make the wax moth an attractive model system.22 Especially in research on bacterial23,24 and fungal17,25-29 pathogenesis, G. mellonella larvae have shown great
*Correspondence to: Gerwald K€ ohler; Email: [email protected] Submitted: 12/10/2014; Accepted: 12/12/2014 http://dx.doi.org/10.1080/21505594.2014.998967
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Downloaded by [University of Bristol] at 03:20 03 March 2015
promise as infection model. In their study, Vilela et al. utilized the larvae as model for infection with the pathogenic yeast Candida albicans and co-infection with a beneficial Lactobacillus acidophilus strain.21 Experimental candidiasis is well established in G. mellonella30-32 and thus an attempt to ameliorate the lethal outcome of the fungal infection by administration of the probiotics is a logical approach to test for probiotic interference with C. albicans pathogenicity. The authors initiated their study by demonstrating anti-Candida effects of the lactobacilli in vitro, i.e., inhibition of fungal filamentation and biofilm formation. Vigorous production of lactic acid by lactobacilli has already been shown to exert antagonistic effects on filamentation and C. albicans cell viability, especially under unbuffered low pH conditions, despite the relatively high acid tolerance of these fungi.33 Additional inhibitory substances produced by the lactobacilli might exacerbate these effects. Vilela et al developed an inoculation
protocol for co-infection and confirmed that the lactobacilli were not pathogenic for the G. mellonella larvae. Subsequently, co-infection experiments revealed that the L. acidophilus strain indeed was able to reduce fungal burden in the larvae and lethality of the infection. The model system also allowed the researchers to perform histological analyses to characterize the effects of the beneficial bacteria on the fungal growth patterns in vivo. The work offers a first proof of concept, but many questions about the probiotic mechanisms encountered in this model remain open. How do the lactobacilli suppress C. albicans in the larvae? What is the role of the insect immune system? Are the findings relevant to probiotic research in humans? In summary, a new invertebrate model to elucidate some aspects of probiotic interference with microbial pathogens has been introduced. The model system has clear advantages such as ease of use and reduced costs, especially in comparison to vertebrate models22. In contrast to
D. melanogaster and C. elegans, pathogenic mechanisms of fungal or bacterial infections and host immune defense mechanisms in G. mellonella appear to correlate more closely with those encountered in humans.22 Conversely, the lack of a complete genome sequence, the absence of reporter and mutant strains, and the need for standardization across different sources and laboratories,22,34 currently dampen the enthusiasm for the G. mellonella model; although future progress is likely to improve upon these drawbacks. In conclusion, G. mellonella has merit as a new model for foundational research on probiotics, but it will certainly not replace the randomized controlled trials in humans so urgently needed to evaluate efficacy of many so-called “probiotics."
References
8. Tilg H, Moschen AR. Microbiota and diabetes: an evolving relationship. Gut 2014; 63:1513-21; PMID:24833634; http://dx.doi.org/10.1136/gutjnl2014-306928 9. Food and Agricultural Organization of the United Nations and World Health Organization. Report of a joint FAO/WHO working group on drafting guidelines for the evaluation of probiotics in food. Food and Agricultural Organization of the United Nations; online, ftp://ftp.fao.org/es/esn/food/wgreport2.pdf. 2002. 10. Reid G, Food, Agricultural Organization of the United N, the WHO. The importance of guidelines in the development and application of probiotics. Curr Pharm Design 2005; 11:11-6; PMID:15638748; http://dx.doi.org/10.2174/1381612053382395 11. Reid G, Kim SO, Kohler GA. Selecting, testing and understanding probiotic microorganisms. FEMS Immunol Med Microbiol 2006; 46:149-57; PMID:16487295; http://dx.doi.org/10.1111/j.1574695X.2005.00026.x 12. Bravo JA, Forsythe P, Chew MV, Escaravage E, Savignac HM, Dinan TG, Bienenstock J, Cryan JF. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci U S A 2011; 108:16050-5; PMID:21876150; http://dx.doi. org/10.1073/pnas.1102999108 13. Gareau MG. Microbiota-gut-brain axis and cognitive function. Adv Exp Med Biol 2014; 817:357-71; PMID:24997042; http://dx.doi.org/10.1007/978-14939-0897-4_16 14. Gioacchini G, Maradonna F, Lombardo F, Bizzaro D, Olivotto I, Carnevali O. Increase of fecundity by probiotic administration in zebrafish (Danio rerio). Reproduction (Cambridge, England) 2010; 140:953-9; PMID:20833753; http://dx.doi.org/10.1530/REP-100145 15. Maradonna F, Gioacchini G, Falcinelli S, Bertotto D, Radaelli G, Olivotto I, Carnevali O. Probiotic supplementation promotes calcification in Danio rerio larvae: a molecular study. PloS One 2013; 8:e83155;
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Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
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