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Differential Role of the T6SS in Acinetobacter baumannii Virulence.

Repizo GD, Gagné S, Foucault-Grunenwald ML, Borges V, Charpentier X, Limansky AS, Gomes JP, Viale AM, Salcedo SP - PLoS ONE (2015)

Bottom Line: The T6SS genomic locus is present and was actively transcribed in all of the above strains.In addition, DSM30011 was able to outcompete ATCC17978 as well as Pseudomonas aeruginosa and Klebsiella pneumoniae, bacterial pathogens relevant in mixed nosocomial infections.Finally, we found that the T6SS of DSM30011 is required for host colonization of the model organism Galleria mellonella suggesting that this system could play an important role in A. baumannii virulence in a strain-specific manner.

View Article: PubMed Central - PubMed

Affiliation: Bases Moléculaires et Structurales des Systèmes Infectieux, CNRS UMR 5086, Université Lyon 1, Institut de Biologie et Chimie des Protéines, Lyon, France.

ABSTRACT
Gram-negative bacteria, such as Acinetobacter baumannii, are an increasing burden in hospitals worldwide with an alarming spread of multi-drug resistant (MDR) strains. Herein, we compared a type strain (ATCC17978), a non-clinical isolate (DSM30011) and MDR strains of A. baumannii implicated in hospital outbreaks (Ab242, Ab244 and Ab825), revealing distinct patterns of type VI secretion system (T6SS) functionality. The T6SS genomic locus is present and was actively transcribed in all of the above strains. However, only the A. baumannii DSM30011 strain was capable of killing Escherichia coli in a T6SS-dependent manner, unlike the clinical isolates, which failed to display an active T6SS in vitro. In addition, DSM30011 was able to outcompete ATCC17978 as well as Pseudomonas aeruginosa and Klebsiella pneumoniae, bacterial pathogens relevant in mixed nosocomial infections. Finally, we found that the T6SS of DSM30011 is required for host colonization of the model organism Galleria mellonella suggesting that this system could play an important role in A. baumannii virulence in a strain-specific manner.

No MeSH data available.


Related in: MedlinePlus

A. baumanni DSM30011 T6SS role in virulence.Comparative survival analysis of G. mellonella larvae inoculated with 5x105 CFU of A. baumannii DSM30011 wild type, its isogenic ΔtssM mutant or complemented strain. Data are representative of three separate survival experiments, each performed with 20 larvae per strain. Survival curves were constructed by the Kaplan-Meier method and compared by log-rank analysis (* P<0.05; n.s.: non-significant).
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pone.0138265.g007: A. baumanni DSM30011 T6SS role in virulence.Comparative survival analysis of G. mellonella larvae inoculated with 5x105 CFU of A. baumannii DSM30011 wild type, its isogenic ΔtssM mutant or complemented strain. Data are representative of three separate survival experiments, each performed with 20 larvae per strain. Survival curves were constructed by the Kaplan-Meier method and compared by log-rank analysis (* P<0.05; n.s.: non-significant).

Mentions: In order to determine if the DSM30011 T6SS fulfils other roles beyond bacterial killing, we further characterized the corresponding ΔtssM strain. The involvement of the T6SS of A. baumannii DSM30011 in virulence was tested in vivo basing on previous established protocols [33]. We first inoculated mice with 108 CFU of the wild-type DSM30011 strain and their weight and health were monitored for 2 days. We found that intraperitoneal (i.p.) inocula of 108 CFU results in death of all mice in less than 24 h most likely from septic shock rather than A. baumannii colonization. On the contrary, a 107 CFU injection dose was found to be sub-lethal, resulting in most mice sick and showing significant weight-loss at 18 h post-inoculation, followed by gradual recovery in the hours after. We therefore selected this dose to i.p. inject mice with a mixed inocula containing the DSM30011 ΔtssM and the parental wild-type strain and obtained a CI of 0.328 ± 0.0547 at 18 h post-inoculation (statistically different from 1, P = 0.008, N = 5). However, due to loss of the plasmid in this model of infection we were not able to complement the mutant phenotype and therefore we could not determine with certainty the role of the A. baumannii DSM30011 T6SS in mice. Therefore, no additional mouse models of infection were tested for ethical reasons and instead, to further evaluate possible roles of the T6SS in A. baumannii DSM30011 virulence, we used G. mellonella killing assays as an alternative infection model. G. mellonella has been widely used for studying the virulence mechanisms of several human pathogens, including A. baumannii [7,34–38]. In addition, the DSM30011 strain was previously shown to be virulent in this model organism [25]. We observed a significant attenuation of the DSM30011 ΔtssM strain that was fully reverted by the expression of tssM from a plasmid (Fig 7). Overall, these results show that the T6SS of the A. baumannii DSM30011 strain is implicated in virulence in contrast to the ATCC17978 strain [10].


Differential Role of the T6SS in Acinetobacter baumannii Virulence.

Repizo GD, Gagné S, Foucault-Grunenwald ML, Borges V, Charpentier X, Limansky AS, Gomes JP, Viale AM, Salcedo SP - PLoS ONE (2015)

A. baumanni DSM30011 T6SS role in virulence.Comparative survival analysis of G. mellonella larvae inoculated with 5x105 CFU of A. baumannii DSM30011 wild type, its isogenic ΔtssM mutant or complemented strain. Data are representative of three separate survival experiments, each performed with 20 larvae per strain. Survival curves were constructed by the Kaplan-Meier method and compared by log-rank analysis (* P<0.05; n.s.: non-significant).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581634&req=5

pone.0138265.g007: A. baumanni DSM30011 T6SS role in virulence.Comparative survival analysis of G. mellonella larvae inoculated with 5x105 CFU of A. baumannii DSM30011 wild type, its isogenic ΔtssM mutant or complemented strain. Data are representative of three separate survival experiments, each performed with 20 larvae per strain. Survival curves were constructed by the Kaplan-Meier method and compared by log-rank analysis (* P<0.05; n.s.: non-significant).
Mentions: In order to determine if the DSM30011 T6SS fulfils other roles beyond bacterial killing, we further characterized the corresponding ΔtssM strain. The involvement of the T6SS of A. baumannii DSM30011 in virulence was tested in vivo basing on previous established protocols [33]. We first inoculated mice with 108 CFU of the wild-type DSM30011 strain and their weight and health were monitored for 2 days. We found that intraperitoneal (i.p.) inocula of 108 CFU results in death of all mice in less than 24 h most likely from septic shock rather than A. baumannii colonization. On the contrary, a 107 CFU injection dose was found to be sub-lethal, resulting in most mice sick and showing significant weight-loss at 18 h post-inoculation, followed by gradual recovery in the hours after. We therefore selected this dose to i.p. inject mice with a mixed inocula containing the DSM30011 ΔtssM and the parental wild-type strain and obtained a CI of 0.328 ± 0.0547 at 18 h post-inoculation (statistically different from 1, P = 0.008, N = 5). However, due to loss of the plasmid in this model of infection we were not able to complement the mutant phenotype and therefore we could not determine with certainty the role of the A. baumannii DSM30011 T6SS in mice. Therefore, no additional mouse models of infection were tested for ethical reasons and instead, to further evaluate possible roles of the T6SS in A. baumannii DSM30011 virulence, we used G. mellonella killing assays as an alternative infection model. G. mellonella has been widely used for studying the virulence mechanisms of several human pathogens, including A. baumannii [7,34–38]. In addition, the DSM30011 strain was previously shown to be virulent in this model organism [25]. We observed a significant attenuation of the DSM30011 ΔtssM strain that was fully reverted by the expression of tssM from a plasmid (Fig 7). Overall, these results show that the T6SS of the A. baumannii DSM30011 strain is implicated in virulence in contrast to the ATCC17978 strain [10].

Bottom Line: The T6SS genomic locus is present and was actively transcribed in all of the above strains.In addition, DSM30011 was able to outcompete ATCC17978 as well as Pseudomonas aeruginosa and Klebsiella pneumoniae, bacterial pathogens relevant in mixed nosocomial infections.Finally, we found that the T6SS of DSM30011 is required for host colonization of the model organism Galleria mellonella suggesting that this system could play an important role in A. baumannii virulence in a strain-specific manner.

View Article: PubMed Central - PubMed

Affiliation: Bases Moléculaires et Structurales des Systèmes Infectieux, CNRS UMR 5086, Université Lyon 1, Institut de Biologie et Chimie des Protéines, Lyon, France.

ABSTRACT
Gram-negative bacteria, such as Acinetobacter baumannii, are an increasing burden in hospitals worldwide with an alarming spread of multi-drug resistant (MDR) strains. Herein, we compared a type strain (ATCC17978), a non-clinical isolate (DSM30011) and MDR strains of A. baumannii implicated in hospital outbreaks (Ab242, Ab244 and Ab825), revealing distinct patterns of type VI secretion system (T6SS) functionality. The T6SS genomic locus is present and was actively transcribed in all of the above strains. However, only the A. baumannii DSM30011 strain was capable of killing Escherichia coli in a T6SS-dependent manner, unlike the clinical isolates, which failed to display an active T6SS in vitro. In addition, DSM30011 was able to outcompete ATCC17978 as well as Pseudomonas aeruginosa and Klebsiella pneumoniae, bacterial pathogens relevant in mixed nosocomial infections. Finally, we found that the T6SS of DSM30011 is required for host colonization of the model organism Galleria mellonella suggesting that this system could play an important role in A. baumannii virulence in a strain-specific manner.

No MeSH data available.


Related in: MedlinePlus