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Environmental Microbiology Reports (2015) 7(1), 6–8
doi:10.1111/1758-2229.12224
Acinetobacter baumanni – understanding and fighting a new emerging pathogen
Beate Averhoff, Molecular Microbiology & Bioenergetics, Goethe University Frankfurt, Frankfurt, Germany. The genus Acinetobacter comprises species well known to all microbiologists. We all know the soil pendant of Escherichia coli, Acinetobacter baylyi that has been invaluable to study unusual metabolic capabilities for microbes such as growth on aromatic compounds. The β-ketoadipate pathway, its biochemistry and genetic regulation has been a treasure for microbiologists for decades (Young et al., 2005). Acinetobacter baylyi and its tremendous capability for deoxyribonucleic acid (DNA) uptake has been an eye opener for students since decades, introducing students to the concept of natural transformation (Averhoff and Graf, 2008). What a surprise when I first learned that there are bacteria that take up naked DNA from the environment, you dont have to torture them, they love to do it. But like Abel has Kain and good has evil, A. baylyi has A. baumannii, a nasty bug that does not enjoy living in the soil but prefers a cozy place in its human or animal host, thereby threatening us and others to hell. In recent decades, A. baumannii has only been found from time to time as an opportunistic pathogen in clinical environments, but recently has set out to conquer the world (Poirel et al., 2011; Visca et al., 2011; Peleg et al., 2012). In recent years it became more and more obvious that A. baumannii can cause life-threatening infections – as recently evidenced by the infections of soldiers in military hospitals after returning from the Iraq war (‘Iraqibacter’) and a growing number of epidemic outbreaks, e.g. in intensive care units all over the world. Acinetobacter baumannii is now among the top 10 pathogens. The broad distribution of the New Dehli β-lactamase (Göttig et al., 2010), the dramatic increase in multi-drug resistance and the recent appearance of even pan drug resistance have disabled the antibiotic arms (Göttig et al., 2014). The multiple resistance traits together with its ability to survive and persist in different environments such as dry surfaces, its ability to adhere and to move, its ability to acquire new genetic material and its metabolic versatility makes this bug an extremely dangerous threat. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd
Alarmingly, little is known about the molecular basis of these metabolic traits, how they function and how they are regulated. Recently, we got a first glimpse on the molecular basis of adaptation to dry surfaces. We identified the compatible solute glycine betaine and the novel compatible solute mannitol to play an important role in osmoadaptation (Sand et al., 2011; 2013; 2014). The latter has so far only been found in one other bacterial genus. Analogous gene clusters are also present in A. baumannii and are suggested to play a similar role (Sand et al., 2014). Moreover, mannitol might also be crucial for adaptation of A. baumannii to the human host because it is a radical scavenger and could mediate the escape from the defence system of the human host. Glycine betaine may be synthesized from exogenous choline but also from choline derived from lecithin by action of phospholipases, known virulence factors in A. baumannii. Choline might serve also as an energy source for A. baumannii, and the elucidation of the intertwining of different regulatory circuits involved in utilization of choline as osmoprotectant or energy source and its role in development of pathogenicity will be a prime focus. The success of A. baumannii to conquer the human host and survive in clinical habitats is attributed to multiple factors: (i) biofilm formation, (ii) resistance to desiccation, (iii) metabolic adaptation, (iv) adherence, colonization and invasion of human epithelial or endothelial cells, (v) multiple antibiotic resistances, (vi) production of siderophores which steel iron from the host, production of quorumsensing molecules which mediate a cross-talk during invasion, (vii) serum resistance to escape the host defence and (viii) phospholipase production. The latter are secreted knifes, for living on a phospholipid diet during host invasion. Moreover, there is substantial evidence in other bacteria that phospholipase cleavage products trigger regulatory cascades thereby supporting host invasion and persistance. The same might hold true for A. baumannii. Unfortunately, the physiological and the molecular basis of all these traits of A. baumannii, i.e. proteins, enzymes and genes involved as well as their regulation by abiotic and biotic factors is largely unknown, and information with respect to the regulation of these virulence factors is scarce.
Crystal ball Elucidation of the molecular basis of the multifactorial nature of A. baumannii pathogenicity requires the application and the development of novel molecular tool boxes. Recently, we developed a novel molecular tool, a marker-less mutagenesis system for A. baumannii which opens new avenues to identify pathogenicity determinants and sheds more light onto the molecular basis of multifactorial pathogenicity and the interplay of the pathogenicity determinants of this emerging pathogen. The multifactorial nature of the A. baumannii pathogenicity raised the primary question: Where do all these pathogenicity traits come from? Preliminary studies indicate a widespread accumulation of multiple mutations and the acquisition of resistance genes. The latter observation might be due to the uptake of different mobile elements from other bacteria and is possibly fostered by the very high genomic plasticity of A. baumannii. These features might have allowed the accumulation of resistance and pathogenicity islands and novel resistance determinants, but this hypothesis remains to be addressed by detailed studies. The final answer to the challenging question where all the pathogenicity and resistance traits come from has not been given yet, but recently it has been shown for the first time that A. baumannii is able to take up free DNA (Wilharm et al., 2013). Interestingly, DNA uptake of A. baumannii is a conditional phenotype only observed while moving on solid surfaces. The latter is dependent on the production of diaminopropane (Skiebe et al., 2012). Now, the time is ripe to integrate all known data and establish a model for the interaction of A. baumannii with its host on a cellular level. To complete the picture of its lifestyle in/on the host and in clinical environments, we need to answer the questions: what does it eat, how does it survive desiccation, what is the role of biofilm formation in persistence, how does it acquire genetic material, how does it move over solid surfaces, where do all these traits come from and what is its natural habitat? All these question culminate in the final goal: understanding the physiology and the molecular basis of adaptation of this emerging pathogen to its eukaryotic host and the clinical environment. This understanding will, in a long run, help to either disarm A. baumannii, by taking preventive measures or to identify new targets for (antibiotic) treatment. But it has to be stated in this context that answers to these burning questions will only be found in an interdisciplinary network of researchers. Only such a network will elucidate the mechanisms of A. baumannii virulence and eukaryotic host cell adaptation from the cellular to the structural level. This network has to employ advanced analytical tools and a broad spectrum of available molecular biological, biochemical, immunological techniques and bioinformatics
7
tools as well as cutting-edge techniques such as nextgeneration sequencing, RNA-seq, deep sequencing, static and dynamic flow infections and novel in vitro and in vivo infection models to achieve the goals and disarm this nasty bug. The German Science Foundation has installed such a research unit last year to address these pressing questions (http://www.bio.uni-frankfurt.de/ 51172482).
Acknowledgement Financial support of our studies with A. baumannii is generously provided by the Deutsche Forschungsgemeinschaft (A. baumannii research unit, Frankfurt).
References Averhoff, B., and Graf, I. (2008) The natural transformation system of Acinetobacter baylyi ADP1: a unique DNA transport machinery. In Acinetobacter Molecular Biology. Gerischer, U. (ed.). Norfolk, UK: Caister Academic Press, pp. 119–140. Göttig, S., Pfeifer, Y., Wichelhaus, T.A., Zacharowski, K., Bingold, T., Averhoff, B., et al. (2010) Global spread of New Dehli metallo-β-lactamase 1. Lancet Infect Dis 10: 828– 829. Göttig, S., Gruber, T.M., Higgins, P.G., Wachsmuth, M., Seifert, H., and Kempf, V.A. (2014) Detection of a pan drug-resistant Acinetobacter baumannii in Germany. J Antimicrob Chemother 69: 2578–2579. Peleg, A.Y., de Breij, A., Adams, M.D., Cerqueira, G.M., Mocali, S., Galardini, M., et al. (2012) The success of Acinetobacter species: genetic, metabolic and viirulence attributes. PLoS ONE 7: e46984. Poirel, L., Bonnin, R.A., and Nordmann, P. (2011) Genetic basis of antibiotic resistance in pathogenic Acinetobacter species. IUBMB Life 63: 1061–1067. Sand, M., de Berardinis, V., Mingote, A., Santos, H., Göttig, S., Müller, V., and Averhoff, B. (2011) Salt adaptation in Acinetobacter baylyi: identification and characterization of a secondary glycine betaine transporter. Arch Microbiol 193: 723–730. Sand, M., Mingote, A.I., Santos, H., Müller, V., and Averhoff, B. (2013) Mannitol, a compatible solute synthesized by Acinetobacter baylyi in a two-step pathway including a salt-induced and salt-dependent mannitol-1phosphate dehydrogenase. Environ Microbiol 15: 2187– 2197. Sand, M., Rodrigues, M., González, J.M., de Crécy-Lagard, V., Santos, H., Müller, V., and Averhoff, B. (2014) Mannitol1-phosphate dehydrogenases/phosphatases: a family of novel bifunctional enzymes for bacterial adaptation to osmotic stress. Environ Microbiol doi:10.1111/14622920.12503. Skiebe, E., de Berardinis, V., Morczinek, P., Kerrinnes, T., Faber, F., Lepka, D., et al. (2012) Surface-associated motility, a common trait of clinical isolates of Acinetobacter baumannii, depends on 1,3-diaminopropane. Int J Med Microbiol 302: 117–128.
© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 7, 6–8
8
Crystal ball
Visca, P., Seifert, H., and Towner, K.J. (2011) Acinetobacter infection – an emerging threat to human health. IUBMB Life 63: 1048–1054. Wilharm, G., Piesker, J., Laue, M., and Skiebe, E. (2013) DNA uptake by the nosocomial pathogen Acinetobacter baumannii occurs during movement along wet surfaces. J Bacteriol 195: 4146–4153.
Young, D.M., Parke, D., and Ornston, L.N. (2005) Opportunities for genetic investigation afforded by Acinetobacter baylyi, a nutritionally versatile bacterial species that is highly competent for natural transformation. Annu Rev Microbiol 59: 519–555.
© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 7, 6–8
Environmental Microbiology Reports (2015) 7(1), 6–8
doi:10.1111/1758-2229.12224
Acinetobacter baumanni – understanding and fighting a new emerging pathogen
Beate Averhoff, Molecular Microbiology & Bioenergetics, Goethe University Frankfurt, Frankfurt, Germany. The genus Acinetobacter comprises species well known to all microbiologists. We all know the soil pendant of Escherichia coli, Acinetobacter baylyi that has been invaluable to study unusual metabolic capabilities for microbes such as growth on aromatic compounds. The β-ketoadipate pathway, its biochemistry and genetic regulation has been a treasure for microbiologists for decades (Young et al., 2005). Acinetobacter baylyi and its tremendous capability for deoxyribonucleic acid (DNA) uptake has been an eye opener for students since decades, introducing students to the concept of natural transformation (Averhoff and Graf, 2008). What a surprise when I first learned that there are bacteria that take up naked DNA from the environment, you dont have to torture them, they love to do it. But like Abel has Kain and good has evil, A. baylyi has A. baumannii, a nasty bug that does not enjoy living in the soil but prefers a cozy place in its human or animal host, thereby threatening us and others to hell. In recent decades, A. baumannii has only been found from time to time as an opportunistic pathogen in clinical environments, but recently has set out to conquer the world (Poirel et al., 2011; Visca et al., 2011; Peleg et al., 2012). In recent years it became more and more obvious that A. baumannii can cause life-threatening infections – as recently evidenced by the infections of soldiers in military hospitals after returning from the Iraq war (‘Iraqibacter’) and a growing number of epidemic outbreaks, e.g. in intensive care units all over the world. Acinetobacter baumannii is now among the top 10 pathogens. The broad distribution of the New Dehli β-lactamase (Göttig et al., 2010), the dramatic increase in multi-drug resistance and the recent appearance of even pan drug resistance have disabled the antibiotic arms (Göttig et al., 2014). The multiple resistance traits together with its ability to survive and persist in different environments such as dry surfaces, its ability to adhere and to move, its ability to acquire new genetic material and its metabolic versatility makes this bug an extremely dangerous threat. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd
Alarmingly, little is known about the molecular basis of these metabolic traits, how they function and how they are regulated. Recently, we got a first glimpse on the molecular basis of adaptation to dry surfaces. We identified the compatible solute glycine betaine and the novel compatible solute mannitol to play an important role in osmoadaptation (Sand et al., 2011; 2013; 2014). The latter has so far only been found in one other bacterial genus. Analogous gene clusters are also present in A. baumannii and are suggested to play a similar role (Sand et al., 2014). Moreover, mannitol might also be crucial for adaptation of A. baumannii to the human host because it is a radical scavenger and could mediate the escape from the defence system of the human host. Glycine betaine may be synthesized from exogenous choline but also from choline derived from lecithin by action of phospholipases, known virulence factors in A. baumannii. Choline might serve also as an energy source for A. baumannii, and the elucidation of the intertwining of different regulatory circuits involved in utilization of choline as osmoprotectant or energy source and its role in development of pathogenicity will be a prime focus. The success of A. baumannii to conquer the human host and survive in clinical habitats is attributed to multiple factors: (i) biofilm formation, (ii) resistance to desiccation, (iii) metabolic adaptation, (iv) adherence, colonization and invasion of human epithelial or endothelial cells, (v) multiple antibiotic resistances, (vi) production of siderophores which steel iron from the host, production of quorumsensing molecules which mediate a cross-talk during invasion, (vii) serum resistance to escape the host defence and (viii) phospholipase production. The latter are secreted knifes, for living on a phospholipid diet during host invasion. Moreover, there is substantial evidence in other bacteria that phospholipase cleavage products trigger regulatory cascades thereby supporting host invasion and persistance. The same might hold true for A. baumannii. Unfortunately, the physiological and the molecular basis of all these traits of A. baumannii, i.e. proteins, enzymes and genes involved as well as their regulation by abiotic and biotic factors is largely unknown, and information with respect to the regulation of these virulence factors is scarce.
Crystal ball Elucidation of the molecular basis of the multifactorial nature of A. baumannii pathogenicity requires the application and the development of novel molecular tool boxes. Recently, we developed a novel molecular tool, a marker-less mutagenesis system for A. baumannii which opens new avenues to identify pathogenicity determinants and sheds more light onto the molecular basis of multifactorial pathogenicity and the interplay of the pathogenicity determinants of this emerging pathogen. The multifactorial nature of the A. baumannii pathogenicity raised the primary question: Where do all these pathogenicity traits come from? Preliminary studies indicate a widespread accumulation of multiple mutations and the acquisition of resistance genes. The latter observation might be due to the uptake of different mobile elements from other bacteria and is possibly fostered by the very high genomic plasticity of A. baumannii. These features might have allowed the accumulation of resistance and pathogenicity islands and novel resistance determinants, but this hypothesis remains to be addressed by detailed studies. The final answer to the challenging question where all the pathogenicity and resistance traits come from has not been given yet, but recently it has been shown for the first time that A. baumannii is able to take up free DNA (Wilharm et al., 2013). Interestingly, DNA uptake of A. baumannii is a conditional phenotype only observed while moving on solid surfaces. The latter is dependent on the production of diaminopropane (Skiebe et al., 2012). Now, the time is ripe to integrate all known data and establish a model for the interaction of A. baumannii with its host on a cellular level. To complete the picture of its lifestyle in/on the host and in clinical environments, we need to answer the questions: what does it eat, how does it survive desiccation, what is the role of biofilm formation in persistence, how does it acquire genetic material, how does it move over solid surfaces, where do all these traits come from and what is its natural habitat? All these question culminate in the final goal: understanding the physiology and the molecular basis of adaptation of this emerging pathogen to its eukaryotic host and the clinical environment. This understanding will, in a long run, help to either disarm A. baumannii, by taking preventive measures or to identify new targets for (antibiotic) treatment. But it has to be stated in this context that answers to these burning questions will only be found in an interdisciplinary network of researchers. Only such a network will elucidate the mechanisms of A. baumannii virulence and eukaryotic host cell adaptation from the cellular to the structural level. This network has to employ advanced analytical tools and a broad spectrum of available molecular biological, biochemical, immunological techniques and bioinformatics
7
tools as well as cutting-edge techniques such as nextgeneration sequencing, RNA-seq, deep sequencing, static and dynamic flow infections and novel in vitro and in vivo infection models to achieve the goals and disarm this nasty bug. The German Science Foundation has installed such a research unit last year to address these pressing questions (http://www.bio.uni-frankfurt.de/ 51172482).
Acknowledgement Financial support of our studies with A. baumannii is generously provided by the Deutsche Forschungsgemeinschaft (A. baumannii research unit, Frankfurt).
References Averhoff, B., and Graf, I. (2008) The natural transformation system of Acinetobacter baylyi ADP1: a unique DNA transport machinery. In Acinetobacter Molecular Biology. Gerischer, U. (ed.). Norfolk, UK: Caister Academic Press, pp. 119–140. Göttig, S., Pfeifer, Y., Wichelhaus, T.A., Zacharowski, K., Bingold, T., Averhoff, B., et al. (2010) Global spread of New Dehli metallo-β-lactamase 1. Lancet Infect Dis 10: 828– 829. Göttig, S., Gruber, T.M., Higgins, P.G., Wachsmuth, M., Seifert, H., and Kempf, V.A. (2014) Detection of a pan drug-resistant Acinetobacter baumannii in Germany. J Antimicrob Chemother 69: 2578–2579. Peleg, A.Y., de Breij, A., Adams, M.D., Cerqueira, G.M., Mocali, S., Galardini, M., et al. (2012) The success of Acinetobacter species: genetic, metabolic and viirulence attributes. PLoS ONE 7: e46984. Poirel, L., Bonnin, R.A., and Nordmann, P. (2011) Genetic basis of antibiotic resistance in pathogenic Acinetobacter species. IUBMB Life 63: 1061–1067. Sand, M., de Berardinis, V., Mingote, A., Santos, H., Göttig, S., Müller, V., and Averhoff, B. (2011) Salt adaptation in Acinetobacter baylyi: identification and characterization of a secondary glycine betaine transporter. Arch Microbiol 193: 723–730. Sand, M., Mingote, A.I., Santos, H., Müller, V., and Averhoff, B. (2013) Mannitol, a compatible solute synthesized by Acinetobacter baylyi in a two-step pathway including a salt-induced and salt-dependent mannitol-1phosphate dehydrogenase. Environ Microbiol 15: 2187– 2197. Sand, M., Rodrigues, M., González, J.M., de Crécy-Lagard, V., Santos, H., Müller, V., and Averhoff, B. (2014) Mannitol1-phosphate dehydrogenases/phosphatases: a family of novel bifunctional enzymes for bacterial adaptation to osmotic stress. Environ Microbiol doi:10.1111/14622920.12503. Skiebe, E., de Berardinis, V., Morczinek, P., Kerrinnes, T., Faber, F., Lepka, D., et al. (2012) Surface-associated motility, a common trait of clinical isolates of Acinetobacter baumannii, depends on 1,3-diaminopropane. Int J Med Microbiol 302: 117–128.
© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 7, 6–8
8
Crystal ball
Visca, P., Seifert, H., and Towner, K.J. (2011) Acinetobacter infection – an emerging threat to human health. IUBMB Life 63: 1048–1054. Wilharm, G., Piesker, J., Laue, M., and Skiebe, E. (2013) DNA uptake by the nosocomial pathogen Acinetobacter baumannii occurs during movement along wet surfaces. J Bacteriol 195: 4146–4153.
Young, D.M., Parke, D., and Ornston, L.N. (2005) Opportunities for genetic investigation afforded by Acinetobacter baylyi, a nutritionally versatile bacterial species that is highly competent for natural transformation. Annu Rev Microbiol 59: 519–555.
© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology Reports, 7, 6–8
