Differential Virulence Contributions of the Efflux Transporter MexAB-OprM in Infecting a Variety of Host Plants.

Efflux transporters such as MexAB-OprM contribute to bacterial resistance to diverse antimicrobial compounds. Here, we show that MexB contributes to epiphytic and late-stage apoplastic growth of strain B728a, as well as lesion formation in common bean (). Although a ∆ mutant formed fewer lesions after topical application to common bean, these lesions contain the same number of cells (10 to 10 cells) as those caused by the wild-type strain. The internalized population size of both the wild-type and the ∆ mutant within small samples of surface-sterilized asymptomatic portions of leaves varied from undetectably low to as high as 10 cells/cm. Localized bacterial populations within individual lesions consistently exceeded 10 cells/cm. Strain B728a was capable of moderate to extensive apoplastic growth in diverse host plants, including lima bean (), fava bean (), pepper (), , sunflower (), and tomato (), but MexB was not required for growth in a subset of these plant species. A model is proposed that MexB provides resistance to as-yet-unidentified antimicrobials that differ between plant species. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.