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Bacteria tracking by in vivo magnetic resonance imaging.

Hoerr V, Tuchscherr L, Hüve J, Nippe N, Loser K, Glyvuk N, Tsytsyura Y, Holtkamp M, Sunderkötter C, Karst U, Klingauf J, Peters G, Löffler B, Faber C - BMC Biol. (2013)

Bottom Line: The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall.With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus.The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical Radiology, University Hospital Münster, Münster 48149, Germany.

ABSTRACT

Background: Different non-invasive real-time imaging techniques have been developed over the last decades to study bacterial pathogenic mechanisms in mouse models by following infections over a time course. In vivo investigations of bacterial infections previously relied mostly on bioluminescence imaging (BLI), which is able to localize metabolically active bacteria, but provides no data on the status of the involved organs in the infected host organism. In this study we established an in vivo imaging platform by magnetic resonance imaging (MRI) for tracking bacteria in mouse models of infection to study infection biology of clinically relevant bacteria.

Results: We have developed a method to label Gram-positive and Gram-negative bacteria with iron oxide nano particles and detected and pursued these with MRI. The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall. Different particle sizes and coatings were tested for their ability to attach to the cell wall and possible labeling mechanisms were elaborated by comparing Gram-positive and -negative bacterial characteristics. With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus. In both a subcutaneous and a systemic infection model induced by iron-labeled S. aureus bacteria, high resolution MR images allowed for bacterial tracking and provided information on the morphology of organs and the inflammatory response.

Conclusion: Labeled with iron oxide particles, in vivo detection of small S. aureus colonies in infection models is feasible by MRI and provides a versatile tool to follow bacterial infections in vivo. The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

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In vitro assays of iron-labeled S. aureus bacteria on HUVEC cells and macrophages. Iron-labeled and non-labeled S. aureus bacteria (strain 6850) were compared to each other with regards to growth behavior, their cytotoxicity and invasiveness in HUVEC cells as well as their phagocytosis by macrophages. (A) In growth curves of S. aureus wild type cells (6850 wt) and electro-competent cells with (6850 comp cells w /iron) and without (6850 comp cell) iron particles, no significant differences were observed for the three cell cultures. (B) The fluorescence microscopic image shows how iron-labeled bacteria are phagocytized by macrophages. (C) In the cytotoxicity assay, cell death of HUVEC cells was compared and quantified upon treatment with S. aureus wild type cells, electro-competent and iron labeled bacteria. (D) In the invasion assay the invasiveness of the laboratory strain Cowan I was set as 100%, the non-invasive laboratory strain TM300 was used as a negative control. Neither growth behavior, cytotoxicity, invasiveness nor phagocytosis by macrophages was affected by the iron label.
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Figure 2: In vitro assays of iron-labeled S. aureus bacteria on HUVEC cells and macrophages. Iron-labeled and non-labeled S. aureus bacteria (strain 6850) were compared to each other with regards to growth behavior, their cytotoxicity and invasiveness in HUVEC cells as well as their phagocytosis by macrophages. (A) In growth curves of S. aureus wild type cells (6850 wt) and electro-competent cells with (6850 comp cells w /iron) and without (6850 comp cell) iron particles, no significant differences were observed for the three cell cultures. (B) The fluorescence microscopic image shows how iron-labeled bacteria are phagocytized by macrophages. (C) In the cytotoxicity assay, cell death of HUVEC cells was compared and quantified upon treatment with S. aureus wild type cells, electro-competent and iron labeled bacteria. (D) In the invasion assay the invasiveness of the laboratory strain Cowan I was set as 100%, the non-invasive laboratory strain TM300 was used as a negative control. Neither growth behavior, cytotoxicity, invasiveness nor phagocytosis by macrophages was affected by the iron label.

Mentions: To exclude a possible influence of the labeling procedure on bacterial cell characteristics we investigated growth behavior as well as cytotoxicity and invasion of iron-labeled bacteria. Growth curves did not differ significantly between untreated cells, and competent cells either with or without iron incubation (Figure 2A). Furthermore, infection models in HUVECs did not reveal differences between iron-labeled and unlabeled bacteria regarding cytotoxicity (Figure 2C) and invasive capacity (Figure 2D).


Bacteria tracking by in vivo magnetic resonance imaging.

Hoerr V, Tuchscherr L, Hüve J, Nippe N, Loser K, Glyvuk N, Tsytsyura Y, Holtkamp M, Sunderkötter C, Karst U, Klingauf J, Peters G, Löffler B, Faber C - BMC Biol. (2013)

In vitro assays of iron-labeled S. aureus bacteria on HUVEC cells and macrophages. Iron-labeled and non-labeled S. aureus bacteria (strain 6850) were compared to each other with regards to growth behavior, their cytotoxicity and invasiveness in HUVEC cells as well as their phagocytosis by macrophages. (A) In growth curves of S. aureus wild type cells (6850 wt) and electro-competent cells with (6850 comp cells w /iron) and without (6850 comp cell) iron particles, no significant differences were observed for the three cell cultures. (B) The fluorescence microscopic image shows how iron-labeled bacteria are phagocytized by macrophages. (C) In the cytotoxicity assay, cell death of HUVEC cells was compared and quantified upon treatment with S. aureus wild type cells, electro-competent and iron labeled bacteria. (D) In the invasion assay the invasiveness of the laboratory strain Cowan I was set as 100%, the non-invasive laboratory strain TM300 was used as a negative control. Neither growth behavior, cytotoxicity, invasiveness nor phagocytosis by macrophages was affected by the iron label.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3686665&req=5

Figure 2: In vitro assays of iron-labeled S. aureus bacteria on HUVEC cells and macrophages. Iron-labeled and non-labeled S. aureus bacteria (strain 6850) were compared to each other with regards to growth behavior, their cytotoxicity and invasiveness in HUVEC cells as well as their phagocytosis by macrophages. (A) In growth curves of S. aureus wild type cells (6850 wt) and electro-competent cells with (6850 comp cells w /iron) and without (6850 comp cell) iron particles, no significant differences were observed for the three cell cultures. (B) The fluorescence microscopic image shows how iron-labeled bacteria are phagocytized by macrophages. (C) In the cytotoxicity assay, cell death of HUVEC cells was compared and quantified upon treatment with S. aureus wild type cells, electro-competent and iron labeled bacteria. (D) In the invasion assay the invasiveness of the laboratory strain Cowan I was set as 100%, the non-invasive laboratory strain TM300 was used as a negative control. Neither growth behavior, cytotoxicity, invasiveness nor phagocytosis by macrophages was affected by the iron label.
Mentions: To exclude a possible influence of the labeling procedure on bacterial cell characteristics we investigated growth behavior as well as cytotoxicity and invasion of iron-labeled bacteria. Growth curves did not differ significantly between untreated cells, and competent cells either with or without iron incubation (Figure 2A). Furthermore, infection models in HUVECs did not reveal differences between iron-labeled and unlabeled bacteria regarding cytotoxicity (Figure 2C) and invasive capacity (Figure 2D).

Bottom Line: The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall.With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus.The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical Radiology, University Hospital Münster, Münster 48149, Germany.

ABSTRACT

Background: Different non-invasive real-time imaging techniques have been developed over the last decades to study bacterial pathogenic mechanisms in mouse models by following infections over a time course. In vivo investigations of bacterial infections previously relied mostly on bioluminescence imaging (BLI), which is able to localize metabolically active bacteria, but provides no data on the status of the involved organs in the infected host organism. In this study we established an in vivo imaging platform by magnetic resonance imaging (MRI) for tracking bacteria in mouse models of infection to study infection biology of clinically relevant bacteria.

Results: We have developed a method to label Gram-positive and Gram-negative bacteria with iron oxide nano particles and detected and pursued these with MRI. The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall. Different particle sizes and coatings were tested for their ability to attach to the cell wall and possible labeling mechanisms were elaborated by comparing Gram-positive and -negative bacterial characteristics. With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus. In both a subcutaneous and a systemic infection model induced by iron-labeled S. aureus bacteria, high resolution MR images allowed for bacterial tracking and provided information on the morphology of organs and the inflammatory response.

Conclusion: Labeled with iron oxide particles, in vivo detection of small S. aureus colonies in infection models is feasible by MRI and provides a versatile tool to follow bacterial infections in vivo. The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

Show MeSH
Related in: MedlinePlus