How Toxoplasma in humans turns aggressive

USDA’s AgResearch Magazine reports that Toxoplasma gondii is a parasite that has infected an estimated one-fourth of the world’s population—potentially more than 1 billion people—including about 50 million in the United States. This makes T. gondii the most widespread parasite in the world. This one-celled parasite, invisible to the naked eye, causes a human disease called “toxoplasmosis.” It can lead to serious health complications in people with weakened immune systems and in infants born to infected mothers. Prevention is key.

toxo.usdaarsT. gondiiinfection can happen in two ways. Cats are the only animals that shed the parasite’s egg-like sacks (cysts) in their feces—thus exposing humans and other animals to infection via contaminated soil, water, food, or litterboxes. Infection can also take place when people consume undercooked meat containing T. gondii. 

Agricultural Research Service (ARS) scientists and colleagues completed a study that provides clues about T. gondii’s virulence and spread. The study describes genetic mechanisms that help a mild-mannered T. gondii strain turn aggressive.

For the study, a consortium of international researchers, including zoologist Benjamin Rosenthal and parasitologist Jitender Dubey, both with the ARS Parasitic Diseases Laboratory in Beltsville, Maryland, contributed strains of T. gondii from more than a dozen countries spanning the Americas, Europe, Africa, and Asia. The researchers conducted a genomic analysis on each of 62 strains and identified several types of proteins, called “secretory pathogenicity determinants” (SPDs) that thwart the hosts’ immunity.

Secreting SPDs enables the parasite to influence and hinder host defenses. “These proteins enhance the parasite’s survival, which in turn affects disease severity in hosts,” says Rosenthal. “SPDs have diversified more in T. gondiithan in species closely related to T. gondii, so we are very curious to learn more about the functions they perform and their relationship to disease.”

The findings are helping researchers to identify the genetic basis for differences among strains of T. gondii, from mild strains found in U.S. farmlands to more virulent strains found in the jungles of Brazil and French Guyana. The researchers found that T. gondii strains could become more aggressive through environmental adaptation.

In healthy people, infection does not necessarily mean a person will become sick or develop symptoms. The study results provide valuable information about a subset of regulatory genes that enable the parasite to infect animals and humans. The findings will help researchers develop new treatments and methods to check the parasite’s ability to spread.


New technology delves deep into pathogenic Salmonella

A highly pathogenic strain of Salmonella, and one resistant to several antimicrobials, has been studied in order to find out how the organism survives and with the aim of pinpointing vulnerability.

salmonella_1Salmonella is an infectious agent with many faces, appearing in a multitude of strains affecting animals and humans. The particular strain is a variant of the bacterium Salmonella enterica serovar Typhimurium. Isolates are more often recovered from blood rather than from the gastrointestinal tract, which makes the organism particularly dangerous. In the affected parts of Africa, the organism has been causing several illnesses in children including many aged under five years.

To explore this organism further, researchers are looking a shear forces and how these affect the progression of the organism. Shearing forces are unaligned forces pushing one part of an organism in one direction, and another part of the organism in the opposite direction. Under high shear forces, the infectious bacteria progresses faster.

Here strain ST313 behaves differently to other types of Salmonella. This suggests the shear forces within the human gut, where most Salmonella infections occur, differ to those in blood. This suggests differences in evolutionary adaption by different strains of the organism.

The studying of bacteria and how they progress, in relation to shear forces, is an emerging sub-field in microbiology. The term “mechanotransduction” (the ability of bacterial cells to sense and respond to physical forces) has been coined for the study area.

To study the ST313 strain, a research group put together a special device called a rotating wall vessel bioreactor. The reactor is designed to culture cells under different fluid shear levels. Through this the ability of ST313 to infect a person, colonize tissue, and cause illness can be studied.

The results to date suggest new strategies should be possible to slowdown progression of the disease in the human body. These could center on altering the resistance of the organism to pH, bile salts and various fluid-derived stress conditions.

The findings are published in the journal npj Microgravity, within a paper titled “Physiological fluid shear alters the virulence potential of invasive multidrug-resistant non-typhoidal Salmonella Typhimurium D23580.”

A survey of Escherichia coli O157:H7 virulence factors: the first 25 years and 13 genomes

Escherichia coli O157:H7 is a human pathogen that was first identified from a foodborne outbreak in 1982, and in the 25 years that followed, many new strains were identified and emerged in numerous outbreaks of human disease. Extensive research has been conducted to identify virulence factor genes involved in the pathogenesis of E. coli O157:H7 and many genome sequences of E. coli O157:H7 strains have become available mason.jones.IIto the scientific community. Here, we provide a comprehensive overview of the research that has been conducted over the first 25 years to identify 394 known or putative virulence factor genes present in the genomes of E. coli O157:H7 strains. Finally, an examination of the conservation of these 394 virulence factor genes across additional genomes of E. coli O157:H7 is provided which summarizes the first 25 years and 13 genomes of this human pathogen. 

Advances in Microbiology, 4, 390-423

Holly A. Reiland, Morrine A. Omolo, Timothy J. Johnson, and David J. Baumler