Description of Research: N. Cary
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
• 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
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.
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.