New Clues on Salmonella
By Jim De
April 28, 1997
Several new studies cast fresh light
on mysteries of Salmonella bacterias infection of chickens. They
also show that, to protect consumers, egg producers can test spleens of mice
from the poultry house to see if they harbor a Salmonella type that
infects chickens more readily. In one study, two years of sampling more than
1,000 mice from commercial poultry houses turned up Salmonella
enteritidis in the spleen of nearly one in five.
Scientists with USDAs Agricultural
Research Service performed the studies with colleagues in the U.S., England and
Salmonella contamination in eggs is rare, but S. enteritidis is the
most common culprit. When consumed by a hen, the bacteria can multiply and
invade organs including the reproductive tract.
S. enteritidis varies in its ability to infect. But researchers now
have identified two of its most serious forms. One, named the lacy phenotype,
is hardier. Compared with ordinary S. enteritidis forms, the lacy
phenotype infects chickens more readily, but its not more likely to
infect eggs or cause disease symptoms. But thats not the case with the
other serious form, called the SE-HCD phenotype (short for S.
enteritidis-high cell density).
Injecting chicks with typical S. enteritidis or the lacy phenotype
rarely kills them. But in tests, the SE-HCD phenotype killed 70 percent in
three days. Current tests indicate it also lowers egg production in adult hens.
Until now, both the lacy phenotype and SE-HCD phenotype were difficult to
study because they were indistinguishable from ordinary types. Also, the SE-HCD
type loses its potent virulence in lab cultures. The researchers now have
identified distinguishing features in carbohydrates called lipopolysaccharides
on the surface of both phenotypes. They also developed the first lab-stable
The latest studies suggest a molecular approach to discovering environmental
triggers that turn ordinary S. enteritidis into the more virulent type.
This could lead to new tactics for lowering the Salmonella threat.
Collaborators with ARS in the studies
included USDAs Food Safety and
Inspection Service, the University of
Pennsylvania, the University of Georgia,
the University of New South
Wales in Australia and, in Britain, the
Public Health Laboratory Service
and Centre for Applied Microbiology
Scientific contact: Jean Guard-Petter, ARS
Southeast Poultry Research Laboratory,
Athens, Ga., phone (706) 546-3446, fax 546-3161,