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Infection and Immunity, December 2001, p. 7873-7879, Vol. 69, No. 12
Division of Environmental
Microbiology1 and Division of Immunology
and Immunopathology,2 Institute for Animal
Health, Compton Laboratory, Compton, Newbury, Berkshire RG20 7NN,
United Kingdom
Received 4 October 2000/Returned for modification 19 February
2001/Accepted 16 August 2001
Salmonella enterica serovar Pullorum is worldwide a
poultry pathogen of considerable economic importance, particularly in those countries with a developing poultry industry. In addition to the
characteristic high mortality rates among young chicks, one of the
features of Salmonella serovar Pullorum infection is that it persists for long periods in convalescent chicks in the absence
of clinical disease. This can lead to colonization of the reproductive
tract of chickens and at sexual maturity can result in infected progeny
through transovarian transmission to eggs. The sites of
Salmonella serovar Pullorum persistence in convalescent
birds are not known, and the mechanisms of persistence are not
understood. Here we show that Salmonella serovar
Pullorum can persist in both the spleen and the reproductive tract for over 40 weeks following experimental infection in chickens. During the
period of sexual maturity, Salmonella serovar Pullorum
colonized both the ovary and the oviduct of hens and led to 6% of laid
eggs being infected by Salmonella serovar Pullorum. The
colonization of several different sites of the reproductive tract
suggests that Salmonella serovar Pullorum may employ
more than one mechanism of egg infection. Persistence occurred despite
a strong humoral response, suggesting an intracellular site of
infection. By use of a Salmonella serovar Pullorum
strain containing a plasmid stably expressing green fluorescent
protein, we demonstrated that the main site of carriage in the spleen
is within macrophages. This raises interesting questions about the
biology of Salmonella serovar Pullorum, including why
there is an increase in bacterial numbers when birds become sexually
mature and in particular how Salmonella serovar Pullorum
avoids clearance by macrophages and whether it modulates the immune
system in other ways.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.12.7873-7879.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Salmonella enterica Serovar Pullorum
Persists in Splenic Macrophages and in the Reproductive Tract during
Persistent, Disease-Free Carriage in Chickens

*
Corresponding author. Mailing address: Division of
Environmental Microbiology, Institute for Animal Health, Compton
Laboratory, Compton, Newbury, Berkshire RG20 7NN, United Kingdom.
Phone: 44-1635-577411. Fax: 44-1635-577236. E-mail:
paul.wigley{at}bbsrc.ac.uk.
Present address: Faculdade de Ciências Agrágarias e
Veterinárias, UNESP, Jaboticabal 14870-000, SP, Brazil.
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