Clinical and environmental isolates of Stenotrophomonas maltophilia cannot be distinguished on the basis of virulence toward invertebrate animals or the ability to protect canola seedlings from plant pathogens.

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Stenotrophomonas maltophilia is emerging as a significant cause of concern for healthcare providers, especially in intensive-care settings where it is associated with a wide variety of complications including ventilator-associated pneumonia and hospital-acquired pneumonia, central line-associated bloodstream infections, surgical site infections, endocarditis, meningitis, ocular infections, and soft tissue, burn and wound infections (Brooke 2012)(refs from R03). Mortality rates attributable to S. maltophilia infection can be extremely high, above 37% in some cases (refs from R03), even after adjusting for underlying conditions. Both the incidence and prevalence of S. maltophilia infection are on the rise (Sader 2005) (other refs from RO3).

In addition to causing opportunistic infection in humans, this Gram-negative, multidrug resistant (MDR) bacterium can often be found in the soil, the rhizosphere of plants, as an endoparasite of amoeba, or in association with other vertebrates including fish, reptiles, and mammals (refs). Interestingly, the interaction between S. maltophilia and plants seems to be a mutually beneficial one (refs). Several groups have found that S. maltophilia isolates can enhance growth and production of agricultural crops (Suckstorff 2003) (add more refs), leading to the suggestion that this bacterium may be useful as a biological additive (Berg 2015). To enable this beneficial use, it is critically important that we are able distinguish between pathogenic and non-pathogenic S. maltophilia isolates.

There have been several previous efforts to identify genotypic features that correlate with virulence in S. maltophilia. between clinical and environmental isolates of S. maltophilia (Alavi 2014)(Adamek 2014) (refs). Unfortunately, these studies only analyzed a handful of isolates, including just a single environmental isolate. In this study, we sought to determine if clinical and environmental isolates differed in how they behaved in functional assays that correspond to virulence and plant growth promotion. We found that environmental S. maltophilia isolates were virulent toward insects and amoeba and that clinical S. maltophilia isolates could protect canola seedlings from plant pathogens. These findings demonstrate that these phenotypes are not exclusive to strains isolated from a particular site. Thus, the successful correlation of S. maltophilia genotypes with virulence and growth promotion phenotypes may require a large number of functionally-characterized isolates.


Like other soil-borne opportunistic pathogens, sm undergoes rapid adaptation to a host environment (ref).

took a functional approach to determine if and sought to determine if clinical and environmental isolates differed in their lethality toward invertebrate animals or in their ability to protect canola seedlings from plant pathogens.

Paragraph on invertebrate hosts.

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Summary statement.

Symbioses between soil bacteria and plants can result in neutral, beneficial, or detrimental effects on plant health. Species from the Gram-negative genus Stenotrophomonas are important members of the rhizosphere community where they participate in nutrient cycling and protection against abiotic stresses such as drought and soil salinity and biotic stresses including pathogenic microorganisms (Alavi 2013) (Kobayashi 1995)(Dunne 2000) (Suckstorff 2003a)(Messiha 2007)(Jin 2011)(Suckstorff 2003)(ref). While isolates can be found associated with a wide variety of plant hosts (Juhnke 1989), they are often the dominant bacterial species associated with cruciferous vegetables (Brassicaceae family) (Ribbeck-Busch 2005) (add more refs).

Stenotrophomonas maltophilia is the founding member of the genus, which was removed from the genus Xanthomonas due to the lack of pathogencity toward plants, a phenotype shared by all other Xanthomonads (Palleroni 1993). Many S. maltophilia strains isolated from the environment protect their host plant from bacterial and fungal pathogens. Strain W81, isolated from the rhizosphere of field-grown sugar beet, produces chitinases and proteases that contribute to growth inhibition of the phytopathogenic fungus Pythium ultimum, resulting in reduction of damping-off disease in soil-grown sugar beet (Dunne 1997). Zhang and Yuen (Zhang 2000)(2000) found that S. maltophilia isolate C3 inhibits germination of conidia of Bipolaris sorokiniana (Sacc.), a cereal pathogen, by a process that also requires chitinase production. Additional strains of S. maltophilia (PD3532, PD3533, PD3534), isolated in the Nile Delta of Egypt, are antagonistic toward Ralstonia solanacearum, the etiological agent of brown rot in potatoes (Messiha 2007). We, therefore, sought to determine if clinical isolates of S. maltophilia could protect canola seedlings from the f