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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR ANALYSIS OF SALMONELLA VIRULENCE, ANTIBIOTIC RESISTANCE, AND HOST RESPONSE Title: Free-Living and Host-Associated Protozoa As Training Camps for Intracellular Pathogens

Authors
item Carlson, Steven
item Franklin, Sharon - SARTEC CORP,ANOKA,MN
item Rasmussen, Mark - SARTEC CORP,ANOKA, MN

Submitted to: Virulence Mechanisms of Bacterial Pathogens
Publication Type: Book / Chapter
Publication Acceptance Date: November 3, 2006
Publication Date: N/A

Interpretive Summary: In 1976, a group of veterans gathered in Philadelphia for a convention. Twenty-nine Legionnaires died from a lung infection that was later termed Legionnaires disease. The pathogen responsible for this malady was found be a bacterium, designated as Legionella pneumophila, that resides inside free-living protozoa. In this outbreak, Legionella was harbored within amoebae that were associated with water-cooling units at the hotel that hosted the convention. Protozoa can ingest bacteria as a nutrient source although some bacteria can survive within the protozoa and then eventually break open the protozoa and escape. Surviving within and self-liberation from protozoa has created opportunities for the pathogen. First, surviving bacteria can acquire the DNA of bacteria that have succumbed to digestive processes inside protozoa. Secondly, the constant insult upon the pathogen can cause the pathogen to express new properties that may be associated with virulence. The bulk of this chapter is devoted to these possibilities with Salmonella serving as a new model pathogen and rumen protozoa, i.e. protozoa that live within the gastrointestinal tract of cattle, functioning as the conduit for changes in the pathogen.

Technical Abstract: In 1976, a group of veterans gathered in Philadelphia for a convention. Twenty-nine Legionnaires died from an acute respiratory infection that was later termed Legionnaires’ disease. The etiologic agent for this malady was found be a bacterium, designated as Legionella pneumophila, that resides inside free-living protozoa. In this outbreak, Legionella was harbored within amoebae that were associated with water-cooling units at the hotel that hosted the convention. Protozoa can ingest bacteria as a nutrient source although some bacteria can survive within the protozoa and then eventually lyse the protozoa. Surviving within and self-liberation from protozoa has created new opportunities for the pathogen. First, surviving bacteria can acquire the DNA of bacteria that have succumbed to digestive processes inside protozoa. Secondly, the constant insult upon the pathogen can lead to new gene expression patterns in which genes are overexpressed, repressed genes become expressed, and cryptic genes yield novel gene products. The bulk of this chapter is devoted to these possibilities with Salmonella serving as a new model pathogen and rumen protozoa functioning as the conduit for changes in the pathogen. Salmonella is an intracellular pathogen readily capable of acquiring new genes and exhibiting new virulence characteristics. Recent studies connect some of these attributes with exposure to protozoa.

Last Modified: 4/20/2014
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