Limits...
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.

Show MeSH

Related in: MedlinePlus

Host immune responses to MRSA infection.D. melanogaster AMP gene induction at 6, 18 and 24 hour post infection was calculated by qRT-PCR as fold change of the transcriptional level in the MRSA infected flies relative to the BHI broth-injected flies: (A) Drosomycin induction; (B) Diptericin induction; (C) Cecropin A1 induction. The asterisk indicates a statistically significantly difference (p = 0.03) between M92 and other MRSA strains in inducing host Cecropin A1 expression at 18 hours post infection (Student’s t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3539928&req=5

Figure 3: Host immune responses to MRSA infection.D. melanogaster AMP gene induction at 6, 18 and 24 hour post infection was calculated by qRT-PCR as fold change of the transcriptional level in the MRSA infected flies relative to the BHI broth-injected flies: (A) Drosomycin induction; (B) Diptericin induction; (C) Cecropin A1 induction. The asterisk indicates a statistically significantly difference (p = 0.03) between M92 and other MRSA strains in inducing host Cecropin A1 expression at 18 hours post infection (Student’s t-test).

Mentions: Drosophila mounts innate responses following bacterial challenge by secreting different antimicrobial peptides (AMPs), such as drosomycin, diptericin, and cecropin A1. We measured the fly host immune response to different MRSA strains in order to determine whether this response correlates with the observed fly killing activity. The induction of drosomycin, diptericin and cecropin A1 in the infected flies was shown as a fold change of transcriptional level relative to the constitutive transcriptional level of these genes in control flies pricked with BHI broth. For all strains, the transcription of all three AMPs was activated post infection. No significant difference in drosomycin or diptericin gene expression was observed among the flies infected with the various strains. (Figure 3A and B). There was a marked difference noted for cecropin A1 gene expression among the various strains. The transcriptional level increased 37- to 54-fold for all flies 6 hours post infection, and 146 to 1253-fold at 18 hours (Figure 3C). At 18 hours, the transcriptional level of cecropin A1 was 146-fold higher in the M92-infected flies than the control flies, which was significantly lower than the fold increase seen in the flies infected with the other strains (642–1253 fold, p=0.03). This difference was also observed at 24 hours post infection, although no statistical difference was observed. Our results demonstrated that different MRSA strains induced similar levels of fly innate immune responses except for M92 which induced much less cecropin A1.


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)

Host immune responses to MRSA infection.D. melanogaster AMP gene induction at 6, 18 and 24 hour post infection was calculated by qRT-PCR as fold change of the transcriptional level in the MRSA infected flies relative to the BHI broth-injected flies: (A) Drosomycin induction; (B) Diptericin induction; (C) Cecropin A1 induction. The asterisk indicates a statistically significantly difference (p = 0.03) between M92 and other MRSA strains in inducing host Cecropin A1 expression at 18 hours post infection (Student’s t-test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539928&req=5

Figure 3: Host immune responses to MRSA infection.D. melanogaster AMP gene induction at 6, 18 and 24 hour post infection was calculated by qRT-PCR as fold change of the transcriptional level in the MRSA infected flies relative to the BHI broth-injected flies: (A) Drosomycin induction; (B) Diptericin induction; (C) Cecropin A1 induction. The asterisk indicates a statistically significantly difference (p = 0.03) between M92 and other MRSA strains in inducing host Cecropin A1 expression at 18 hours post infection (Student’s t-test).
Mentions: Drosophila mounts innate responses following bacterial challenge by secreting different antimicrobial peptides (AMPs), such as drosomycin, diptericin, and cecropin A1. We measured the fly host immune response to different MRSA strains in order to determine whether this response correlates with the observed fly killing activity. The induction of drosomycin, diptericin and cecropin A1 in the infected flies was shown as a fold change of transcriptional level relative to the constitutive transcriptional level of these genes in control flies pricked with BHI broth. For all strains, the transcription of all three AMPs was activated post infection. No significant difference in drosomycin or diptericin gene expression was observed among the flies infected with the various strains. (Figure 3A and B). There was a marked difference noted for cecropin A1 gene expression among the various strains. The transcriptional level increased 37- to 54-fold for all flies 6 hours post infection, and 146 to 1253-fold at 18 hours (Figure 3C). At 18 hours, the transcriptional level of cecropin A1 was 146-fold higher in the M92-infected flies than the control flies, which was significantly lower than the fold increase seen in the flies infected with the other strains (642–1253 fold, p=0.03). This difference was also observed at 24 hours post infection, although no statistical difference was observed. Our results demonstrated that different MRSA strains induced similar levels of fly innate immune responses except for M92 which induced much less cecropin A1.

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