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Path-Immuno - James Versalovic Lab

Houston, Texas

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Path-Immuno - James Versalovic Lab
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Coreen Johnson, Ph.D.

Coreen JohnsonPostdoctoral Associate

Phone: 832-824-3409
Fax: 832-825-116
Joined lab: Nov. 2010

Mailing Address:
Texas Children's Hospital
1102 Bates Ave.
Suite 830, Feigin Center
Houston, TX 77030

Research Interests

Characterization of the histidine decarboxylase gene cluster in Lactobacillus reuteri

Lactobacillus reuteri, a Gram-positive lactic acid-producing bacterium, is indigenous to the gastrointestinal tract of humans. Lactic acid bacteria generate biogenic amines via metabolic conversions, generating biological signals with compounds such as histamine. Our lab recently demonstrated that histamine secreted by L. reuteri was able to modulate the host immune response by inhibiting a known pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-α).

Histamine synthesis results from the decarboxylation of the amino acid histidine to histamine by histidine decarboxylases, a process which results in the secretion of histamine into the environment through a transporter. Analysis of the sequenced Lactobacillus genomes has revealed that L. reuteri 6475 is one of the few beneficial microbes known to possess the necessary and complete set of genes required to synthesize and transport histamine. The histidine decarboxylase (hdc) gene cluster includes hdcA (a putative histidine decarboxylase), hdcB (a protein with unknown function), hdcP (a putative antiporter) and HisS (a possible regulator of histamine production). Dr Johnson aims to assess four basic questions:

  1. Which of the hdc gene products are necessary for the conversion of external histidine to histamine.
  2. Where do the hdc proteins localize.
  3. Which of the hdc gene products are necessary for the repression of host cytokines.
  4. How is the synthesis of histamine regulated in L reuteri. We believe this work will contribute to a greater understanding of the role of beneficial microbes in the gastrointestinal tract.


  • Ph.D. Microbiology and Immunology, UTHSCSA, San Antonio, TX, 2003-2010
  • Certification in Medical Technology MT (ASCP), Austin State Hospital, 1999-2000
  • Bachelor of Science, Microbiology, The University of Texas at Austin, 1996-1999
  • Undergraduate coursework, The University of Texas at Arlington, 1994-1995


Coreen Johnson, TR Kannan, JB Baseman. (2008). Identification of a Potential Virulence Determinant in Mycoplasma penetrans. International Organization of Mycoplasmology, Tianjin, China.


Johnson C, Kannan TR, and Baseman JB. 2009. Characterization of a Unique ADP-Ribosyltransferase of Mycoplasma penetrans. Infect Immun 77(10): 4362-4370.

Johnson C, Kannan TR, and Baseman JB. 2010. Cellular vacuoles induced by Mycoplasma pneumoniae CARDS toxin originate from Rab9-associated compartments. PLoS One. 2011;6(7):e22877.

Johnson C and Versalovic J. 2011. The Human Microbiome and Its Potential Importance to Pediatrics. Review submitted.

Professional Memberships

American Society of Microbiology

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