Description of Research: N. Cary Engleberg

For the past 20 years, my research has focused on problems of bacterial pathogenesis at the molecular level. After many years of interest in Legionnaires’ disease (see references below), the focus of laboratory shifted to the regulation of virulence in Streptococcus pyogenes in the late 1990s. Currently, the laboratory is also beginning a project in an unrelated area of interest -- the detection of infectious agents using novel reagents.

• Pathogenesis of streptococcal skin lesions

Interest in this pathogen began with the observation that a two-component regulator of S. pyogenes (CsrRS) is a repressor of several of the virulence factors associated with necrotizing skin infection in animals. We also found that spontaneous mutations in this regulator occur frequently during mouse infection generating hypervirulent clones that synergize with wild type streptococci to produce larger, more destructive skin lesions and increased mortality.
Mutational analysis of some of the individual factors regulated by CsrRS (specifically, streptolysin S, hyaluronic acid capsule, pyrogenic exotoxin B, and streptokinase) yielded insight about their respective roles in the production of skin lesions in a mouse model. For example, streptolysin S is required for rapid spreading of infection and lethality, whereas pyrogenic exotoxin B is necessary for sloughing of the epidermis over areas of subcutaneous infection and development of open ulcers. While streptolysin S is indiscriminately toxic to all mammalian cells, pyrogenic exotoxin B is a cysteine proteinase that may have activity in dissociating epidermal cells from one another.

It had been known that plasminogen from animals are poor substrates for the action of S. pyogenes streptokinase. So, in collaboration with colleagues from other divisions, we demonstrated that streptokinase is a human-host specific virulence factor. Streptokinase contributes to systemic dissemination of S. pyogenes from the skin of mice when purified human plasminogen is given exogenously or when transgenic mice expressing human plasminogen are infected.

Current work in the laboratory is directed at the enzyme hyaluronidase and its putative regulator (which is not CsrRS). Our findings to date confirm that hyaluronidase acts on tissue hyaluronic acid but does not appreciably impact the deployment of the streptococcal capsule (also composed of hyaluronic acid). Although we showed that hyaluronidase facilitates the diffusion of large molecules through tissue surrounding streptococcal skin infection, it does not facilitate the spread of bacteria per se. The principle function of this classic virulence factor may be nutrition, rather than dissemination of streptococci.

• Diagnosis of infectious diseases using RNA aptamers:

Based on their primary sequence, RNA molecules form secondary structures that can bind to surfaces much in the way that antibodies do. However, there are several advantages to antibodies, e.g., RNA can easily be synthesized, purified, labeled in various ways, and detected using PCR. In collaboration with members of our Biological Chemistry department, we are generating RNAs that bind to pathogens that are notoriously difficult to detect or are not immunogenic. This project is in its infancy at present, but we have been able to use a fluorescent-labeled RNA aptamer to detect specific particles in biological samples (in the manner of a fluorescent antibody test). We are currently isolating RNA aptamers that bind to fungal pathogens.

Recent publications:

Young, M., Aronoff, D.M., Engleberg, N.C. Necrotizing fasciitis: a review of pathogenesis and treatment. Expert Rev. Anti Infect. Ther. 2005; 3: 279-94.

Starr CR, Engleberg NC. Role of hyaluronidase in subcutaneous spread and growth of group A streptococcus. Infect Immunity 74: 40-48, 2006.

Young MH, Engleberg NC, Mulla ZD, Aronoff DM. Therapies for necrotising fasciitis. Expert Opin Biol Ther 6 (2): 155-165, 2006.

Yax JA, Famon EC, Engleberg NC. Successful Immunization of an Allogeneic Bone Marrow Transplant Recipient with Live, Attenuated Yellow Fever Vaccine. J Travel Med 16 (5): 365-367, 2009.