Dr. Kim Cowles

Although bacterial human pathogens, such as Salmonella enterica, are usually studied in the context of their animal hosts, it has become increasingly apparent that a significant portion of their life cycle occurs on plants. This adaptation to the plant environment has led to increased incidence of human disease, particularly in the context of fresh produce. The fundamental biology of Salmonella in the plant environment remains vastly ill-defined and little is known about biological factors that enhance survival on plants. Her project focuses on the role of the host in the tri-trophic interaction between bacterium – phytophagous insect – plant. The co-association of phytophagous insects, such as the Aster leafhopper, Macrosteles quadrilineatus, results in S. enterica populations that persist at higher levels for longer periods of time when compared to plants treated with S. enterica alone. We hypothesized that leafhoppers increase S. enterica persistence by altering the plant defense response to the benefit of the bacteria. Leafhopper infestation activates the jasmonic acid (JA) defense response while S. enterica colonization triggers the salicylic acid (SA) response. In tomato plants co-treated with S. enterica and leafhoppers, both JA- and SA-inducible genes were activated, suggesting that the presence of leafhoppers may affect the crosstalk that occurs between the two antagonistic immune response pathways. To rule out the possibility that leafhoppers provide additional benefits to S. enterica, plants will be treated with chemical analogs of JA or SA to activate each immune response in the absence of leafhoppers. By investigating the interaction between this human pathogen, a common phytophagous insect, and their plant host, we hope to elucidate the mechanisms promoting S. enterica survival on plants and provide information to be used in the development of new food safety intervention strategies

Education and Research Experience

Postdoctoral Fellow, Department of Molecular Biology, Princeton University, Princeton, NJ, 2006-2011 (NIAID Ruth L. Kirschstein National Research Service Award, 2008-2011)
Ph.D., Microbiology, University of Wisconsin-Madison, 2006
B.S., Microbiology, University of Illinois-Urbana-Champaign, 2000 (summa cum laude)


Cowles, KN, Willis, DK, Engle, TN, Jones, JB, and Barak, JD. 2016. Diguanylate cyclases, AdrA and STM1987, regulate Salmonella enterica exopolysaccharide production during plant colonization in an environment-dependent manner. Appl. Environ. Microbiol. 82(4): 1237-1248. Link

Merritt, JH, Ha, DG, Cowles, KN, Lu, W, Morales, DK, Rabinowitz, J, Gitai, Z, and O’Toole, GA. 2010 Specific control of Pseudomonas aeruginosa surface-associated behaviors by two c-di-GMP diguanylate cyclases. MBio. 19:1(4). Pii e00183-10. Link

Cowles, KN and Gitai, Z. 2010 Surface association and the MreB cytoskeleton regulate pilus production, localization and function in Pseudomonas aeruginosa. Mol Microbiol. 76(6):1411-26. Link

Herbert, EE, Cowles, KN, and Goodrich-Blair, H. 2007 CpxRA regulates mutualism and pathogenesis in Xenorhabdus nematophila. Appl Environ Microbiol. 73(24):7826-36. Link

Cowles KN, Cowles CE, Richards GR, Martens EC, Goodrich-Blair H. 2007 The global regulator Lrp contributes to mutualism, pathogenesis and phenotypic variation in the bacterium Xenorhabdus nematophila. Cell Microbiol. 9(5):1311-23. Link

Park Y, Herbert EE, Cowles CE, Cowles KN, Menard ML, Orchard SS, Goodrich-Blair H. 2007 Clonal variation in Xenorhabdus nematophila virulence and suppression of Manduca sexta immunity. Cell Microbiol. 9(3):645-56. Link

Cowles KN, Goodrich-Blair H. 2005 Expression and activity of a Xenorhabdus nematophila haemolysin required for full virulence towards Manduca sexta insects. Cell Microbiol. 7(2):209-19. Link