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Acinetobacter baumannii secretes cytotoxic outer membrane protein A via outer membrane vesicles.

Jin JS, Kwon SO, Moon DC, Gurung M, Lee JH, Kim SI, Lee JC - PLoS ONE (2011)

Bottom Line: Potential virulence factors, including AbOmpA and tissue-degrading enzymes, were associated with A. baumannii OMVs.The OMVs from A. baumannii ATCC 19606(T) induced apoptosis of host cells, whereas this effect was not detected in the OMVs from the ΔompA mutant, thereby reflecting AbOmpA-dependent host cell death.In conclusion, the OMV-mediated delivery of virulence factors to host cells may well contribute to pathogenesis during A. baumannii infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Kyungpook National University School of Medicine, Daegu, Korea.

ABSTRACT
Acinetobacter baumannii is an important nosocomial pathogen that causes a high morbidity and mortality rate in infected patients, but pathogenic mechanisms of this microorganism regarding the secretion and delivery of virulence factors to host cells have not been characterized. Gram-negative bacteria naturally secrete outer membrane vesicles (OMVs) that play a role in the delivery of virulence factors to host cells. A. baumannii has been shown to secrete OMVs when cultured in vitro, but the role of OMVs in A. baumannii pathogenesis is not well elucidated. In the present study, we evaluated the secretion and delivery of virulence factors of A. baumannii to host cells via the OMVs and assessed the cytotoxic activity of outer membrane protein A (AbOmpA) packaged in the OMVs. A. baumannii ATCC 19606(T) secreted OMVs during in vivo infection as well as in vitro cultures. Potential virulence factors, including AbOmpA and tissue-degrading enzymes, were associated with A. baumannii OMVs. A. baumannii OMVs interacted with lipid rafts in the plasma membranes and then delivered virulence factors to host cells. The OMVs from A. baumannii ATCC 19606(T) induced apoptosis of host cells, whereas this effect was not detected in the OMVs from the ΔompA mutant, thereby reflecting AbOmpA-dependent host cell death. The N-terminal region of AbOmpA(22-170) was responsible for host cell death. In conclusion, the OMV-mediated delivery of virulence factors to host cells may well contribute to pathogenesis during A. baumannii infection.

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Related in: MedlinePlus

A. baumannii OMVs contain biologically active proteins.(A) A. baumannii OMVs were incubated with 100 mM nitrocefin in PBS at 30°C for 30 min. Hydrolysis of nitrocefin was monitored at 480 nm using a UV spectrophotometer. Inlet figure: left, brown colorization of nitrocefin in A. baumannii OMVs; right, negative control of nitrocefin in PBS. (B) SDS-PAGE of proteins packaged in the OMVs from A. baumannii ATCC 19606T (lanes 1 and 2) and its Western blot analysis (lanes 3 and 4). The samples were immunoblotted with a rabbit anti-AbOmpA immune serum. Lanes 1 and 3, molecular weight maker; 2 and 4, OMV fraction. Arrows indicate AbOmpA.
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pone-0017027-g002: A. baumannii OMVs contain biologically active proteins.(A) A. baumannii OMVs were incubated with 100 mM nitrocefin in PBS at 30°C for 30 min. Hydrolysis of nitrocefin was monitored at 480 nm using a UV spectrophotometer. Inlet figure: left, brown colorization of nitrocefin in A. baumannii OMVs; right, negative control of nitrocefin in PBS. (B) SDS-PAGE of proteins packaged in the OMVs from A. baumannii ATCC 19606T (lanes 1 and 2) and its Western blot analysis (lanes 3 and 4). The samples were immunoblotted with a rabbit anti-AbOmpA immune serum. Lanes 1 and 3, molecular weight maker; 2 and 4, OMV fraction. Arrows indicate AbOmpA.

Mentions: In order to determine whether AmpC β-lactamase (A1S_2367) identified in the A. baumannii OMVs were biologically active, the prepared OMVs were incubated with the β-lactamase substrate, nitrocefin. This showed that the β-lactamases associated with A. baumannii OMVs degraded nitrocefin, as demonstrated by the colorization of nitrocefin (Fig. 2A). Moreover, the results of Western blot analysis demonstrated that the full length of AbOmpA with a molecular mass of 38.4 kDa was detected in the A. baumannii OMVs (Fig. 2B). These results indicate that A. baumannii OMVs harbor biologically active virulence factors and enzymes, which can perform diverse biologic processes in host cells.


Acinetobacter baumannii secretes cytotoxic outer membrane protein A via outer membrane vesicles.

Jin JS, Kwon SO, Moon DC, Gurung M, Lee JH, Kim SI, Lee JC - PLoS ONE (2011)

A. baumannii OMVs contain biologically active proteins.(A) A. baumannii OMVs were incubated with 100 mM nitrocefin in PBS at 30°C for 30 min. Hydrolysis of nitrocefin was monitored at 480 nm using a UV spectrophotometer. Inlet figure: left, brown colorization of nitrocefin in A. baumannii OMVs; right, negative control of nitrocefin in PBS. (B) SDS-PAGE of proteins packaged in the OMVs from A. baumannii ATCC 19606T (lanes 1 and 2) and its Western blot analysis (lanes 3 and 4). The samples were immunoblotted with a rabbit anti-AbOmpA immune serum. Lanes 1 and 3, molecular weight maker; 2 and 4, OMV fraction. Arrows indicate AbOmpA.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046175&req=5

pone-0017027-g002: A. baumannii OMVs contain biologically active proteins.(A) A. baumannii OMVs were incubated with 100 mM nitrocefin in PBS at 30°C for 30 min. Hydrolysis of nitrocefin was monitored at 480 nm using a UV spectrophotometer. Inlet figure: left, brown colorization of nitrocefin in A. baumannii OMVs; right, negative control of nitrocefin in PBS. (B) SDS-PAGE of proteins packaged in the OMVs from A. baumannii ATCC 19606T (lanes 1 and 2) and its Western blot analysis (lanes 3 and 4). The samples were immunoblotted with a rabbit anti-AbOmpA immune serum. Lanes 1 and 3, molecular weight maker; 2 and 4, OMV fraction. Arrows indicate AbOmpA.
Mentions: In order to determine whether AmpC β-lactamase (A1S_2367) identified in the A. baumannii OMVs were biologically active, the prepared OMVs were incubated with the β-lactamase substrate, nitrocefin. This showed that the β-lactamases associated with A. baumannii OMVs degraded nitrocefin, as demonstrated by the colorization of nitrocefin (Fig. 2A). Moreover, the results of Western blot analysis demonstrated that the full length of AbOmpA with a molecular mass of 38.4 kDa was detected in the A. baumannii OMVs (Fig. 2B). These results indicate that A. baumannii OMVs harbor biologically active virulence factors and enzymes, which can perform diverse biologic processes in host cells.

Bottom Line: Potential virulence factors, including AbOmpA and tissue-degrading enzymes, were associated with A. baumannii OMVs.The OMVs from A. baumannii ATCC 19606(T) induced apoptosis of host cells, whereas this effect was not detected in the OMVs from the ΔompA mutant, thereby reflecting AbOmpA-dependent host cell death.In conclusion, the OMV-mediated delivery of virulence factors to host cells may well contribute to pathogenesis during A. baumannii infection.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Kyungpook National University School of Medicine, Daegu, Korea.

ABSTRACT
Acinetobacter baumannii is an important nosocomial pathogen that causes a high morbidity and mortality rate in infected patients, but pathogenic mechanisms of this microorganism regarding the secretion and delivery of virulence factors to host cells have not been characterized. Gram-negative bacteria naturally secrete outer membrane vesicles (OMVs) that play a role in the delivery of virulence factors to host cells. A. baumannii has been shown to secrete OMVs when cultured in vitro, but the role of OMVs in A. baumannii pathogenesis is not well elucidated. In the present study, we evaluated the secretion and delivery of virulence factors of A. baumannii to host cells via the OMVs and assessed the cytotoxic activity of outer membrane protein A (AbOmpA) packaged in the OMVs. A. baumannii ATCC 19606(T) secreted OMVs during in vivo infection as well as in vitro cultures. Potential virulence factors, including AbOmpA and tissue-degrading enzymes, were associated with A. baumannii OMVs. A. baumannii OMVs interacted with lipid rafts in the plasma membranes and then delivered virulence factors to host cells. The OMVs from A. baumannii ATCC 19606(T) induced apoptosis of host cells, whereas this effect was not detected in the OMVs from the ΔompA mutant, thereby reflecting AbOmpA-dependent host cell death. The N-terminal region of AbOmpA(22-170) was responsible for host cell death. In conclusion, the OMV-mediated delivery of virulence factors to host cells may well contribute to pathogenesis during A. baumannii infection.

Show MeSH
Related in: MedlinePlus