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Helene Andrews-Polymenis

Helene Andrews-Polymenis

Associate Professor

Department of Microbial and Molecular Pathogenesis

Texas A&M Health Science Center

Room 470 Reynolds Medical Building
1114 TAMU

College Station , TX 77843-1114
Office Phone: (979) 845-9438


  1. A.B. Biology, Brown University, 1989
  2. Ph.D. Tufts University School of Medicine, 1999
  3. D.V.M. Texas A&M College of Veterinary Medicine, 2001
  4. Post-doc., Texas A&M University, Laboratory of Andreas Baumler


Research Projects

Introduction to Salmonellae

Members of the genus Salmonellae cause ~1.4 million cases of food-borne diarrheal disease annually in the United States, associated with approximately 500 deaths (Mead et al. 1999; Voetsch et al. 2004). Worldwide, these organisms are responsible for hundreds of millions of cases of salmonellosis and hundreds of thousands of deaths. Typhoid fever is a serious systemic illness caused by typhoidal serotypes of Salmonellae (Typhi, Paratyphi A and B) that is not prevalent in the United States but causes hundreds of thousands of deaths worldwide. In addition to diarrheal disease, systemic illness and bacteremia can also result from infection with non-Typhoidal Salmonellae (NTS). Children under the age of 5 are most frequently infected with diarrheal NTS  (20% of isolations in the United States in 2005) and along with the elderly and immuno-compromised are at high risk for the development of fatal systemic salmonellosis after NTS infection. Although NTS are the most frequent cause of death associated with food-borne infectious agents in the US, the total number of such cases in this country is relatively low. However, around the world where large portions of the population are immunocompromised, especially in sub-Saharan Africa where HIV infection rates have risen dramatically, infection with non-typhoidal Salmonellae cause systemic disease with high frequency and with high rates of fatality (Alausa et al. 1977; Gordon et al. 2001; Gordon et al. 2002; Kankwatira et al. 2004).

Despite the importance of this food borne pathogen and over 30 years of intensive study, much of the biology of the Salmonellae in the various niches in their complete life cycle- is still poorly understood. We hope to contribute to the identification and characterization of genes involved in many aspects of the complete life cycle of this organism using functional genomics and characterization of the molecular roles of the genes we identify.

1. Functional Genomics of Salmonellae

We are generating a library of targeted deletions using λ red recombination in all non-essential genes of Salmonella enterica serotype Typhimurium ATCC14028 in collaboration with Dr. Michael McClelland (SDIBR, San Diego).  We currently have generated targeted deletions in  approx. 1000 genes specific to Salmonellae, or approximately ¼ of the genome, and are progressing to complete this collection. Please see this citation (link will be inserted shortly when paper is online)  for all the details of our mutant collection, and the custom microarray used to assay the pooled library during selection.

2. Genetic Basis of NTS Bacteremia

We are using the power of complete genome sequences and forward genetics to identify novel genes that allow a bacterial pathogen to colonize systemic organs. Non-typhoidal Salmonella (NTS) are food-borne bacterial pathogens that cause hundreds of millions of cases of diarrheal disease and hundreds of thousands of deaths due to bacteremia annually worldwide. Salmonella enterica serotype Typhimurium (STm) is an appropriate model to determine the requirements for systemic infection by NTS, as this serotype causes more cases of NTS bacteremia, especially in children under the age of 5 and in HIV infected individuals, than any other serotype. The availability of complete genome sequence information, and the ease of genetic manipulation make serot. Typhimurium an excellent model system. We are using our collection of targeted deletion strains in  serot. Typhimurium and a novel microarray, to complete  forward genetic screening of our mutant collection of systemic colonization.  We have already identified approximately 40  STm genes not previously implicated in systemic infection, and in addition to completing our screen, we are working to determine the molecular role of these genes during systemic infection.

3. Genetics of Salmonella Resistance to the Inflammatory Response in the Gut

Non-typhoidal Salmonella, including serotype Typhimurium (STm) are food-borne bacterial pathogens that cause ~1.4 million cases of diarrheal disease annually in the United States and hundreds of millions of cases worldwide. In the intestine, STm induces a strong neutrophilic inflammatory response and the production of antimicobial compounds by intestinal epithelial cells. In the face of this inflammatory response the numbers of STm in the intestine increase sharply, while the intestinal microflora of the host are dramatically reduced. Our objective is to identify the bacterial factors that allow STm to resist being killed by antimicrobials produced by the intestinal epithelium. We have developed a forward genetic system to make screening for mutants feasible in ligated ileal loops using our collection of targeted deletions, to identify those that are specifically selected against during intestinal inflammation.  This project is a first step toward a comprehensive determination of the molecular mechanism of the bacterial genes involved in the response to inflammation in the gut.

4. Genetic Basis of Intestinal Persistence of Salmonella enterica

The vast majority of Salmonella infections in mammals and birds are the result of infection with S. enterica subspecies I serovars, yet very few genetic factors that are necessary for intestinal persistence in these reservoirs have been described. Intestinal persistence is critical for shedding and transmission of serovar Typhimurium in mammals and birds, yet this phenomenon and interaction of the organism with the host immune system during persistent infection is poorly understood. A long-term goal of our work is to understand the genetic basis of intestinal persistence of Salmonella enterica.

We are approaching this problem from two perspectives:

a. Studying the molecular role of individual genes we know to be important for persistence in the intestine and fecal shedding.

We are investigating the role STM0557, a ssp. I specific gene, and surrounding genes STM0558 and 0559 in the ability of Typhimurium to persist in the intestine. Nonpolar deletion mutants in STM0557, 0558 and 0559 are all defective for intestinal persistence in competitive infections with wild type ATCC14028. All three of these genes are located on a recently described pathogenicity island termed SPI-16 (4, Vernikos & Parkhill 2006), and are orthologs of the  gtrA,B, gtr (type) cluster in seroconverting bacteriophage.  The proteins encoded by these genes change the composition of the O-antigen subunits by addition of a glucose to these repeating structures (insert link to paper here).  In Salmonella these genes are be involved in ‘form variation’, of the O12 antigen by addition of a glucose to the 4 position of the galactose of the O12 antigen. We are currently interested in the regulation and function of these genes in intestinal persistence.

b. Screening our targeted deletion library for genes necessary for intestinal persistence.

We are interested in the ability of Salmonellae to perisist in the mammalian and avian intestine, because this ability is central to transmission of the organism and to the safety of the human food supply . We are currently screening our library of deletions to identify mutants that are unable to persist in the intestinal tract.

Selected Publications:

Santiviago, C.A., Reynolds, M.M., Porwollik, S., Choi, S.H., Long, F., Andrews-Polymenis, H.L., and McClelland, M. 2009. Analysis of Pools of Targeted Salmonella Deletion Mutants Identifies Novel Genes Affecting Fitness during Competitive Infection in Mice. PLoS Pathogens 5.

Andrews-Polymenis, H.L., Santiviago, C.A., and McClelland, M. 2009. Novel genetic tools for studying food-borne Salmonella. Current Opinion in Biotechnology 20: 149-157.

Sivula, C.P., Bogomolnaya, L.M., and Andrews-Polymenis, H.L. 2008. A comparison of cecal colonization of Salmonella enterica serotype Typhimurium in white leghorn chicks and Salmonella-resistant mice. BMC Microbiology 8.

Lenz, L.L. and Andrews-Polymenis, H.L. 2008. Silencing the alarm: insights into the interaction between host and pathogen - Conference on microbial pathogenesis: Mechanisms of infectious disease. EMBO Reports 9: 27-32.

Bogomolnaya, L.M., Santiviago, C.A., Yang, H.J., Baumler, A.J., and Andrews-Polymenis, H.L. 2008. 'Form variation' of the O12 antigen is critical for persistence of Salmonella Typhimurium in the murine intestine. Molecular Microbiology 70: 1105-1119.

Tukel, C., Raffatellu, M., Humphries, A.D., Wilson, R.P., Andrews-Polymenis, H.L., Gull, T., Figueiredo, J.F., Wong, M.H., Michelsen, K.S., Akcelik, M. et al. 2005. CsgA is a pathogen-associated molecular pattern of Salmonella enterica serotype Typhimurium that is recognized by Toll-like receptor 2. Molecular Microbiology 58: 289-304.

Raffatellu, M., Sun, Y.H., Wilson, R.P., Tran, Q.T., Chessa, D., Andrews-Polymenis, H.L., Lawhon, S.D., Figueiredo, J.F., Tsolis, R.M., Adams, L.G. et al. 2005. Host restriction of Salmonella enterica serotype Typhi is not caused by functional alteration of SipA, SopB, or SopD. Infection and Immunity 73: 7817-7826.

Andrews-Polymenis, H.L., Rabsch, W., Porwollik, S., McClelland, M., Rosetti, C., Adams, L.G., and Baumler, A.J. 2004. Host restriction of Salmonella enterica serotype typhimurium pigeon isolates does not correlate with loss of discrete genes. Journal of Bacteriology 186: 2619-2628.

Rabsch, W., Andrews, H.L., Kingsley, R.A., Prager, R., Tschape, H., Adams, L.G., and Baumler, A.J. 2002. Salmonella enterica serotype Typhimurium and its host-adapted variants. Infection and Immunity 70: 2249-2255.

Watarai, M., Andrews, H.L., and Isberg, R.R. 2001. Formation of a fibrous structure on the surface of Legionella pneumophila associated with exposure of DotH and DotO proteins after intracellular growth. Molecular Microbiology 39: 313-329.

Vogel, J.P., Andrews, H.L., Wong, S.K., and Isberg, R.R. 1998. Conjugative transfer by the virulence system of Legionella pneumophila. Science 279: 873-876.

Kirby, J.E., Vogel, J.P., Andrews, H.L., and Isberg, R.R. 1998. Evidence for pore-forming ability by Legionella pneumophila. Molecular Microbiology 27: 323-336.

Andrews, H.L., Vogel, J.P., and Isberg, R.R. 1998. Identification of linked Legionella pneumophila genes essential for intracellular growth and evasion of the endocytic pathway. Infection and Immunity 66: 950-958.

Book Chapters:

Andrews-Polymenis, H.L., Dorsey, C.W., Raffatellu, M., and Baümler, A.J. 2006. Expression, function, and in vivo identification of Salmonella virulence factors. In Salmonella infections: clinical, immunological and molecular aspects (ed. P. Mastroeni). Cambridge University Press.

Andrews-Polymenis, H.L. and Baümler, A.J. 2005. Salmonella ssp. In Pathogenomics (eds. J. Hacker and U. Dobrindt). WILEY-VCH Verlag GmbH, Weinheim.

Publications from Genetic Graduate Students:

Santiviago, C.A., Reynolds, M.M., Porwollik, S., Choi, S.H., Long, F., Andrews-Polymenis, H.L., and McClelland, M. 2009. Analysis of Pools of Targeted Salmonella Deletion Mutants Identifies Novel Genes Affecting Fitness during Competitive Infection in Mice. Plos Pathogens 5.

Grants arising from Preliminary Data Generated by Genetics Graduate Students:

1. Identification of Salmonella Genes Important for Systemic Colonization, NIH/NIAID 1R01AI083646-01 

2. Genetics of Salmonella Resistance to the Inflammatory Response in the Gut, NIH/NIAID R21AI083964-01

3. Identification of Salmonella Genes Involved in Persistence in Murine Intestine, NIH/NIAID 1R56AI077645-01A1


Megan Reynolds