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Comparative analysis of surface-exposed virulence factors of Acinetobacter baumannii.

Eijkelkamp BA, Stroeher UH, Hassan KA, Paulsen IT, Brown MH - BMC Genomics (2014)

Bottom Line: Acinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates.This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate.Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, Flinders University, Adelaide, Australia. melissa.brown@flinders.edu.au.

ABSTRACT

Background: Acinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates. Genome data have revealed that A. baumannii is highly genetically diverse, which correlates with major variations seen at the phenotypic level. Thus far, comparative genomic studies have been aimed at identifying resistance determinants in A. baumannii. In this study, we extend and expand on these analyses to gain greater insight into the virulence factors across eight A. baumannii strains which are clonally, temporally and geographically distinct, and includes an isolate considered non-pathogenic and a community-acquired A. baumannii.

Results: We have identified a large number of genes in the A. baumannii genomes that are known to play a role in virulence in other pathogens, such as the recently studied proline-alanine-alanine-arginine (PAAR)-repeat domains of the type VI secretion systems. Not surprising, many virulence candidates appear to be part of the A. baumannii core genome of virulent isolates but were often found to be insertionally disrupted in the avirulent A. baumannii strain SDF. Our study also reveals that many known or putative virulence determinants are restricted to specific clonal lineages, which suggests that these virulence determinants may be crucial for the success of these widespread common clones. It has previously been suggested that the high level of intrinsic and adaptive resistance has enabled the widespread presence of A. baumannii in the hospital environment. This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate.

Conclusions: Major genetic variation in known or putative virulence factors was seen across the eight strains included in this study, suggesting that virulence mechanisms are complex and multifaceted in A. baumannii. Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species.

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Genetic analysis of the Type I pili clusters. Genomic organization of the Type I pili clusters A1S_1507-1510, AB57_2003-2007, A1S_2088-2091 and A1S_2213-2218 (Csu-cluster) in ATCC 17978 and comparison to those in other strains. Genes have been drawn to scale. The arrows represent ORFs and depict the direction of transcription; pili components (black), adjacent homologous genes (grey), transposases (red) and inactivated genes (blue). The blue shading indicate a high level of homology between genes from different strains (E-value <10-30). The asterisks indicate the location of a polymeric tract seen in A1S_2091 and its ortholog in strain ATCC 19606T.
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Fig2: Genetic analysis of the Type I pili clusters. Genomic organization of the Type I pili clusters A1S_1507-1510, AB57_2003-2007, A1S_2088-2091 and A1S_2213-2218 (Csu-cluster) in ATCC 17978 and comparison to those in other strains. Genes have been drawn to scale. The arrows represent ORFs and depict the direction of transcription; pili components (black), adjacent homologous genes (grey), transposases (red) and inactivated genes (blue). The blue shading indicate a high level of homology between genes from different strains (E-value <10-30). The asterisks indicate the location of a polymeric tract seen in A1S_2091 and its ortholog in strain ATCC 19606T.

Mentions: One of the most common protein structures decorating the outer surface of pathogens are the Type I pili, which often play a major role in adherence of Gram-negative pathogens, and are well documented in another member of the gamma-proteobacteria, uropathogenic Escherichia coli[34]. Four gene clusters encoding these pili have been identified in A. baumannii (Figure 2), which include the functionally characterized csu-cluster (A1S_2213-2218) [35–37]. Interestingly, the csu-cluster is likely to be non-functional in two strains; in ACICU as a result of an insertion, and in ATCC 17978 due to a single nucleotide polymorphism resulting in truncation of csuB, as previously described [3]. At a proteomic level, the P pili annotated proteins (cluster AB57_2003-2007), CsuC and CsuD, and putative Type III pili (Table 2; A1S_0690-0695), were found to be highly expressed in cells in the pellicle [38] perhaps highlighting their role in this phenotype.Figure 2


Comparative analysis of surface-exposed virulence factors of Acinetobacter baumannii.

Eijkelkamp BA, Stroeher UH, Hassan KA, Paulsen IT, Brown MH - BMC Genomics (2014)

Genetic analysis of the Type I pili clusters. Genomic organization of the Type I pili clusters A1S_1507-1510, AB57_2003-2007, A1S_2088-2091 and A1S_2213-2218 (Csu-cluster) in ATCC 17978 and comparison to those in other strains. Genes have been drawn to scale. The arrows represent ORFs and depict the direction of transcription; pili components (black), adjacent homologous genes (grey), transposases (red) and inactivated genes (blue). The blue shading indicate a high level of homology between genes from different strains (E-value <10-30). The asterisks indicate the location of a polymeric tract seen in A1S_2091 and its ortholog in strain ATCC 19606T.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4256060&req=5

Fig2: Genetic analysis of the Type I pili clusters. Genomic organization of the Type I pili clusters A1S_1507-1510, AB57_2003-2007, A1S_2088-2091 and A1S_2213-2218 (Csu-cluster) in ATCC 17978 and comparison to those in other strains. Genes have been drawn to scale. The arrows represent ORFs and depict the direction of transcription; pili components (black), adjacent homologous genes (grey), transposases (red) and inactivated genes (blue). The blue shading indicate a high level of homology between genes from different strains (E-value <10-30). The asterisks indicate the location of a polymeric tract seen in A1S_2091 and its ortholog in strain ATCC 19606T.
Mentions: One of the most common protein structures decorating the outer surface of pathogens are the Type I pili, which often play a major role in adherence of Gram-negative pathogens, and are well documented in another member of the gamma-proteobacteria, uropathogenic Escherichia coli[34]. Four gene clusters encoding these pili have been identified in A. baumannii (Figure 2), which include the functionally characterized csu-cluster (A1S_2213-2218) [35–37]. Interestingly, the csu-cluster is likely to be non-functional in two strains; in ACICU as a result of an insertion, and in ATCC 17978 due to a single nucleotide polymorphism resulting in truncation of csuB, as previously described [3]. At a proteomic level, the P pili annotated proteins (cluster AB57_2003-2007), CsuC and CsuD, and putative Type III pili (Table 2; A1S_0690-0695), were found to be highly expressed in cells in the pellicle [38] perhaps highlighting their role in this phenotype.Figure 2

Bottom Line: Acinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates.This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate.Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, Flinders University, Adelaide, Australia. melissa.brown@flinders.edu.au.

ABSTRACT

Background: Acinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates. Genome data have revealed that A. baumannii is highly genetically diverse, which correlates with major variations seen at the phenotypic level. Thus far, comparative genomic studies have been aimed at identifying resistance determinants in A. baumannii. In this study, we extend and expand on these analyses to gain greater insight into the virulence factors across eight A. baumannii strains which are clonally, temporally and geographically distinct, and includes an isolate considered non-pathogenic and a community-acquired A. baumannii.

Results: We have identified a large number of genes in the A. baumannii genomes that are known to play a role in virulence in other pathogens, such as the recently studied proline-alanine-alanine-arginine (PAAR)-repeat domains of the type VI secretion systems. Not surprising, many virulence candidates appear to be part of the A. baumannii core genome of virulent isolates but were often found to be insertionally disrupted in the avirulent A. baumannii strain SDF. Our study also reveals that many known or putative virulence determinants are restricted to specific clonal lineages, which suggests that these virulence determinants may be crucial for the success of these widespread common clones. It has previously been suggested that the high level of intrinsic and adaptive resistance has enabled the widespread presence of A. baumannii in the hospital environment. This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate.

Conclusions: Major genetic variation in known or putative virulence factors was seen across the eight strains included in this study, suggesting that virulence mechanisms are complex and multifaceted in A. baumannii. Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species.

Show MeSH
Related in: MedlinePlus