Limits...
Colonization of plants by human pathogenic bacteria in the course of organic vegetable production.

Hofmann A, Fischer D, Hartmann A, Schmid M - Front Microbiol (2014)

Bottom Line: In addition, plant species dependent effects were observed.Spinach was colonized more often and at lower inoculation doses compared to corn salad.Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Research Unit Microbe-Plant Interactions, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH) Neuherberg, Germany.

ABSTRACT
In recent years, increasing numbers of outbreaks caused by the consumption of vegetables contaminated with human pathogenic bacteria were reported. The application of organic fertilizers during vegetable production is one of the possible reasons for contamination with those pathogens. In this study laboratory experiments in axenic and soil systems following common practices in organic farming were conducted to identify the minimal dose needed for bacterial colonization of plants and to identify possible factors like bacterial species or serovariation, plant species or organic fertilizer types used, influencing the success of plant colonization by human pathogenic bacteria. Spinach and corn salad were chosen as model plants and were inoculated with different concentrations of Salmonella enterica sv. Weltevreden, Listeria monocytogenes sv. 4b and EGD-E sv. 1/2a either directly (axenic system) or via agricultural soil amended with spiked organic fertilizers (soil system). In addition to PCR- and culture-based detection methods, fluorescence in situ hybridization (FISH) was applied in order to localize bacteria on or in plant tissues. Our results demonstrate that shoots were colonized by the pathogenic bacteria at inoculation doses as low as 4 × 10 CFU/ml in the axenic system or 4 × 10(5) CFU/g in the soil system. In addition, plant species dependent effects were observed. Spinach was colonized more often and at lower inoculation doses compared to corn salad. Differential colonization sites on roots, depending on the plant species could be detected using FISH-CLSM analysis. Furthermore, the transfer of pathogenic bacteria to plants via organic fertilizers was observed more often and at lower initial inoculation doses when fertilization was performed with inoculated slurry compared to inoculated manure. Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases.

No MeSH data available.


Related in: MedlinePlus

CLSM image of a spinach root hair. The plant seedling was inoculated for 1 h with S. enterica sv. Weltevreden at an inoculation density of 4 × 106 CFU/ml. The plant was harvested after 3 weeks of growth in an axenic system. Probe Cy3 marked EUB-338, I, II, III was applied during FISH procedure (red signal).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4017148&req=5

Figure 1: CLSM image of a spinach root hair. The plant seedling was inoculated for 1 h with S. enterica sv. Weltevreden at an inoculation density of 4 × 106 CFU/ml. The plant was harvested after 3 weeks of growth in an axenic system. Probe Cy3 marked EUB-338, I, II, III was applied during FISH procedure (red signal).

Mentions: In order to localize the inoculated bacteria on the roots of spinach and corn salad and to identify preferential colonization sites, a combined FISH/CLSM analysis was conducted. Salmonella enterica sv. Weltevreden was found to colonize spinach roots preferentially in the root hair zone. It was detected both, on the surface of the root hairs (Figure 1) as well as in cell interspaces of the main root in this zone (Figure 2). On corn salad roots the bacteria were mainly detected on the surface of root tip cells (Figure 3A) and rarely in the root hair zone (data not shown). On the root tip even a colonization of the glycocalix was observed (Figure 3B). Listeria monocytogenes sv. 4b colonized spinach roots in the root hair zone in cell interspaces of the root (Figure 4). It was not detected on root hairs or on the root tips (data not shown). Corn salad plants were mainly colonized by L. monocytogenes sv. 4b shortly behind the root tip but were not detected at the root tip (Figure 5). They were also found in cell interspaces of older root parts, but only in rare cases and small numbers (Figure 5).


Colonization of plants by human pathogenic bacteria in the course of organic vegetable production.

Hofmann A, Fischer D, Hartmann A, Schmid M - Front Microbiol (2014)

CLSM image of a spinach root hair. The plant seedling was inoculated for 1 h with S. enterica sv. Weltevreden at an inoculation density of 4 × 106 CFU/ml. The plant was harvested after 3 weeks of growth in an axenic system. Probe Cy3 marked EUB-338, I, II, III was applied during FISH procedure (red signal).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4017148&req=5

Figure 1: CLSM image of a spinach root hair. The plant seedling was inoculated for 1 h with S. enterica sv. Weltevreden at an inoculation density of 4 × 106 CFU/ml. The plant was harvested after 3 weeks of growth in an axenic system. Probe Cy3 marked EUB-338, I, II, III was applied during FISH procedure (red signal).
Mentions: In order to localize the inoculated bacteria on the roots of spinach and corn salad and to identify preferential colonization sites, a combined FISH/CLSM analysis was conducted. Salmonella enterica sv. Weltevreden was found to colonize spinach roots preferentially in the root hair zone. It was detected both, on the surface of the root hairs (Figure 1) as well as in cell interspaces of the main root in this zone (Figure 2). On corn salad roots the bacteria were mainly detected on the surface of root tip cells (Figure 3A) and rarely in the root hair zone (data not shown). On the root tip even a colonization of the glycocalix was observed (Figure 3B). Listeria monocytogenes sv. 4b colonized spinach roots in the root hair zone in cell interspaces of the root (Figure 4). It was not detected on root hairs or on the root tips (data not shown). Corn salad plants were mainly colonized by L. monocytogenes sv. 4b shortly behind the root tip but were not detected at the root tip (Figure 5). They were also found in cell interspaces of older root parts, but only in rare cases and small numbers (Figure 5).

Bottom Line: In addition, plant species dependent effects were observed.Spinach was colonized more often and at lower inoculation doses compared to corn salad.Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Research Unit Microbe-Plant Interactions, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH) Neuherberg, Germany.

ABSTRACT
In recent years, increasing numbers of outbreaks caused by the consumption of vegetables contaminated with human pathogenic bacteria were reported. The application of organic fertilizers during vegetable production is one of the possible reasons for contamination with those pathogens. In this study laboratory experiments in axenic and soil systems following common practices in organic farming were conducted to identify the minimal dose needed for bacterial colonization of plants and to identify possible factors like bacterial species or serovariation, plant species or organic fertilizer types used, influencing the success of plant colonization by human pathogenic bacteria. Spinach and corn salad were chosen as model plants and were inoculated with different concentrations of Salmonella enterica sv. Weltevreden, Listeria monocytogenes sv. 4b and EGD-E sv. 1/2a either directly (axenic system) or via agricultural soil amended with spiked organic fertilizers (soil system). In addition to PCR- and culture-based detection methods, fluorescence in situ hybridization (FISH) was applied in order to localize bacteria on or in plant tissues. Our results demonstrate that shoots were colonized by the pathogenic bacteria at inoculation doses as low as 4 × 10 CFU/ml in the axenic system or 4 × 10(5) CFU/g in the soil system. In addition, plant species dependent effects were observed. Spinach was colonized more often and at lower inoculation doses compared to corn salad. Differential colonization sites on roots, depending on the plant species could be detected using FISH-CLSM analysis. Furthermore, the transfer of pathogenic bacteria to plants via organic fertilizers was observed more often and at lower initial inoculation doses when fertilization was performed with inoculated slurry compared to inoculated manure. Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases.

No MeSH data available.


Related in: MedlinePlus