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Assessment of virulence diversity of methicillin-resistant Staphylococcus aureus strains with a Drosophila melanogaster infection model.

Wu K, Conly J, Surette M, Sibley C, Elsayed S, Zhang K - BMC Microbiol. (2012)

Bottom Line: These results correlate with bacterial virulence in the Caenorhabditis elegans host model as well as human clinical data.Our results demonstrate that the D. melanogaster model is potentially useful for studying S. aureus pathogenicity.Different MRSA strains demonstrated diverse virulence in the D. melanogaster model, which may be the result of differing expression of bacterial virulence factors in vivo.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology & Laboratory Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, Canada.

ABSTRACT

Background: Staphylococcus aureus strains with distinct genetic backgrounds have shown different virulence in animal models as well as associations with different clinical outcomes, such as causing infection in the hospital or the community. With S. aureus strains carrying diverse genetic backgrounds that have been demonstrated by gene typing and genomic sequences, it is difficult to compare these strains using mammalian models. Invertebrate host models provide a useful alternative approach for studying bacterial pathogenesis in mammals since they have conserved innate immune systems of biological defense. Here, we employed Drosophila melanogaster as a host model for studying the virulence of S. aureus strains.

Results: Community-associated methicillin-resistant S. aureus (CA-MRSA) strains USA300, USA400 and CMRSA2 were more virulent than a hospital-associated (HA)-MRSA strain (CMRSA6) and a colonization strain (M92) in the D. melanogaster model. These results correlate with bacterial virulence in the Caenorhabditis elegans host model as well as human clinical data. Moreover, MRSA killing activities in the D. melanogaster model are associated with bacterial replication within the flies. Different MRSA strains induced similar host responses in D. melanogaster, but demonstrated differential expression of common bacterial virulence factors, which may account for the different killing activities in the model. In addition, hemolysin α, an important virulence factor produced by S. aureus in human infections is postulated to play a role in the fly killing.

Conclusions: Our results demonstrate that the D. melanogaster model is potentially useful for studying S. aureus pathogenicity. Different MRSA strains demonstrated diverse virulence in the D. melanogaster model, which may be the result of differing expression of bacterial virulence factors in vivo.

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Comparison of 5 virulence gene expression profiles between different MRSA strains. (A) Fold-change in the transcriptional level for each gene in MRSA at stationary phase relative to the level in bacteria at mid-log phase in vitro (BHI broth); (B) Fold-change in the transcriptional level for each gene of MRSA strains relative to the level of M92 at mid-log phase in vitro (BHI broth); (C) Fold-change in the transcriptional level of each gene in MRSA strains relative to the level of M92 at 18 hour in the flies post infection (in vivo). The asterisk indicates a statistically significantly difference (p < 0.05) of the in vivo virulence gene expression in the MRSA strains as compared with M92 (Student’s t-test). Hemolysin α (hla): USA300 vs M92, p=0.0013; USA400 vs M92, p=0.038; and CMRSA2 vs M92, p=0.0015. Staphylokinase (sak): USA300 vs M92, p=0.006; USA400 vs M92, p=0.007; CMRSA2 vs M92, p=0.0698.
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Figure 4: Comparison of 5 virulence gene expression profiles between different MRSA strains. (A) Fold-change in the transcriptional level for each gene in MRSA at stationary phase relative to the level in bacteria at mid-log phase in vitro (BHI broth); (B) Fold-change in the transcriptional level for each gene of MRSA strains relative to the level of M92 at mid-log phase in vitro (BHI broth); (C) Fold-change in the transcriptional level of each gene in MRSA strains relative to the level of M92 at 18 hour in the flies post infection (in vivo). The asterisk indicates a statistically significantly difference (p < 0.05) of the in vivo virulence gene expression in the MRSA strains as compared with M92 (Student’s t-test). Hemolysin α (hla): USA300 vs M92, p=0.0013; USA400 vs M92, p=0.038; and CMRSA2 vs M92, p=0.0015. Staphylokinase (sak): USA300 vs M92, p=0.006; USA400 vs M92, p=0.007; CMRSA2 vs M92, p=0.0698.

Mentions: The first comparison that was made for virulence gene expression was between the mid-log and stationary phases of bacteria grown in BHI broth. The expressions of hla, hlg and sak were higher in the stationary phase than in the mid-log phase for all strains (Figure 4A), which is consistent with previous studies [21-23]. The expressions of sspA and hysA were higher in the mid-log phase for some strains, suggesting that the expression of these genes varied among strains. We subsequently compared the virulence gene expression of S. aureus strains against that of M92 in vitro (Figure 4B). All strains were found to have lower hla expression than M92 in vitro, but varied in the expression of other genes, with no specific pattern noted. When in vivo virulence gene expression was examined, it was noted that hla expression was significantly higher in all high virulence strains (USA300, USA400 and CMRSA2; p values: 0.0013, 0.038 and 0.0015, respectively) but not in the low virulence strain CMRSA6 as compared with M92 (Figure 4C). High in vivo expression of sak and sspA were also observed in the high virulence strains but not all of them exhibited significant difference (sak, p values: 0.006, 0.007 and 0.0698 for USA300, USA400 and CMRSA2, respectively; sspA, all p > 0.05) (Figure 4C). The other genes displayed different gene expression patterns in different strains without correlation with fly killing activity. CMRSA6, a low virulence strain, showed lower in vivo gene expression compared with M92 for all genes tested.


Assessment of virulence diversity of methicillin-resistant Staphylococcus aureus strains with a Drosophila melanogaster infection model.

Wu K, Conly J, Surette M, Sibley C, Elsayed S, Zhang K - BMC Microbiol. (2012)

Comparison of 5 virulence gene expression profiles between different MRSA strains. (A) Fold-change in the transcriptional level for each gene in MRSA at stationary phase relative to the level in bacteria at mid-log phase in vitro (BHI broth); (B) Fold-change in the transcriptional level for each gene of MRSA strains relative to the level of M92 at mid-log phase in vitro (BHI broth); (C) Fold-change in the transcriptional level of each gene in MRSA strains relative to the level of M92 at 18 hour in the flies post infection (in vivo). The asterisk indicates a statistically significantly difference (p < 0.05) of the in vivo virulence gene expression in the MRSA strains as compared with M92 (Student’s t-test). Hemolysin α (hla): USA300 vs M92, p=0.0013; USA400 vs M92, p=0.038; and CMRSA2 vs M92, p=0.0015. Staphylokinase (sak): USA300 vs M92, p=0.006; USA400 vs M92, p=0.007; CMRSA2 vs M92, p=0.0698.
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Related In: Results  -  Collection

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Figure 4: Comparison of 5 virulence gene expression profiles between different MRSA strains. (A) Fold-change in the transcriptional level for each gene in MRSA at stationary phase relative to the level in bacteria at mid-log phase in vitro (BHI broth); (B) Fold-change in the transcriptional level for each gene of MRSA strains relative to the level of M92 at mid-log phase in vitro (BHI broth); (C) Fold-change in the transcriptional level of each gene in MRSA strains relative to the level of M92 at 18 hour in the flies post infection (in vivo). The asterisk indicates a statistically significantly difference (p < 0.05) of the in vivo virulence gene expression in the MRSA strains as compared with M92 (Student’s t-test). Hemolysin α (hla): USA300 vs M92, p=0.0013; USA400 vs M92, p=0.038; and CMRSA2 vs M92, p=0.0015. Staphylokinase (sak): USA300 vs M92, p=0.006; USA400 vs M92, p=0.007; CMRSA2 vs M92, p=0.0698.
Mentions: The first comparison that was made for virulence gene expression was between the mid-log and stationary phases of bacteria grown in BHI broth. The expressions of hla, hlg and sak were higher in the stationary phase than in the mid-log phase for all strains (Figure 4A), which is consistent with previous studies [21-23]. The expressions of sspA and hysA were higher in the mid-log phase for some strains, suggesting that the expression of these genes varied among strains. We subsequently compared the virulence gene expression of S. aureus strains against that of M92 in vitro (Figure 4B). All strains were found to have lower hla expression than M92 in vitro, but varied in the expression of other genes, with no specific pattern noted. When in vivo virulence gene expression was examined, it was noted that hla expression was significantly higher in all high virulence strains (USA300, USA400 and CMRSA2; p values: 0.0013, 0.038 and 0.0015, respectively) but not in the low virulence strain CMRSA6 as compared with M92 (Figure 4C). High in vivo expression of sak and sspA were also observed in the high virulence strains but not all of them exhibited significant difference (sak, p values: 0.006, 0.007 and 0.0698 for USA300, USA400 and CMRSA2, respectively; sspA, all p > 0.05) (Figure 4C). The other genes displayed different gene expression patterns in different strains without correlation with fly killing activity. CMRSA6, a low virulence strain, showed lower in vivo gene expression compared with M92 for all genes tested.

Bottom Line: These results correlate with bacterial virulence in the Caenorhabditis elegans host model as well as human clinical data.Our results demonstrate that the D. melanogaster model is potentially useful for studying S. aureus pathogenicity.Different MRSA strains demonstrated diverse virulence in the D. melanogaster model, which may be the result of differing expression of bacterial virulence factors in vivo.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology & Laboratory Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, Canada.

ABSTRACT

Background: Staphylococcus aureus strains with distinct genetic backgrounds have shown different virulence in animal models as well as associations with different clinical outcomes, such as causing infection in the hospital or the community. With S. aureus strains carrying diverse genetic backgrounds that have been demonstrated by gene typing and genomic sequences, it is difficult to compare these strains using mammalian models. Invertebrate host models provide a useful alternative approach for studying bacterial pathogenesis in mammals since they have conserved innate immune systems of biological defense. Here, we employed Drosophila melanogaster as a host model for studying the virulence of S. aureus strains.

Results: Community-associated methicillin-resistant S. aureus (CA-MRSA) strains USA300, USA400 and CMRSA2 were more virulent than a hospital-associated (HA)-MRSA strain (CMRSA6) and a colonization strain (M92) in the D. melanogaster model. These results correlate with bacterial virulence in the Caenorhabditis elegans host model as well as human clinical data. Moreover, MRSA killing activities in the D. melanogaster model are associated with bacterial replication within the flies. Different MRSA strains induced similar host responses in D. melanogaster, but demonstrated differential expression of common bacterial virulence factors, which may account for the different killing activities in the model. In addition, hemolysin α, an important virulence factor produced by S. aureus in human infections is postulated to play a role in the fly killing.

Conclusions: Our results demonstrate that the D. melanogaster model is potentially useful for studying S. aureus pathogenicity. Different MRSA strains demonstrated diverse virulence in the D. melanogaster model, which may be the result of differing expression of bacterial virulence factors in vivo.

Show MeSH
Related in: MedlinePlus