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New Strategy for Developing Rapid Diagnostics

An international consortium of researchers has devised a novel strategy for developing rapid, inexpensive diagnostic tests for microbial infections.

Effective treatment of microbial infection is critically dependent on early diagnosis and identification of the causative organism. One inexpensive, rapid and adaptable to point-of-care diagnostic method is immunoassay for microbial antigens that are shed into bodily fluids during infection. A major barrier to developing these diagnostics is determining which of the hundreds or thousands of antigens produced by the pathogen are actually present in patient samples in detectable amounts.

Using a technique they call In vivo Microbial Antigen Discovery (InMAD),the researchers amplifed the small signals present in an infected mouse's blood by purifying serum samples and using them to immunize another mouse. The resulting "InMAD immune serum" from the second mouse, which contains antibodies specific for the soluble microbial antigens present in sera from the infected mice, is then used to probe blots of bacterial lysates or bacterial proteome arrays.

The spots on the blot or the array that light up indicate the antigens to which the mouse immune system reacted. These are the antigens that could be targeted in an immunoassay.

Using the InMAD system, they successfully identified antigens that could be used in rapid diagnostics for the biothreats Burkholderia pseudomallei and Francisella tularensis.


How Q Fever Invades and Replicates Inside Killer Immune Cells

As part of its life cycle Coxiella burnetii, the bacterial pathogen responsible for Q fever, replicates inside a membrane-bound compartment or "parasitophorous vacuole" (PV) within immune cells. The organism manipulates macrophages to create the PV as well as optimal conditions for growth.

Circumstantial evidence has suggested that C. burnetii is able to exert this control using proteins that are delivered via a mechanism called a Dot/Icm type IVB secretion system (T4BSS) which is critical for successful parasitism of macrophages by the organism.

Using new genetic tools, researchers from the National Institute of Allergy and Infectious Diseases and the University of Arkansas for Medical Science have finally verified that Dot/Icm function is in fact essential for productive infection of human macrophages by C. burnetii.


Protein Necessary for Bacteria to Produce Ulcers

When it comes to the ability of the bacterium Helicobacter pylori to effectively colonize the stomach and eventually cause ulcers it all comes down to a single protein.

H. pylori strains infect half of all humans worldwide and contribute to the development of peptic ulcers and gastric cancer. They cannot survive the harsh acidic environment inside stomach cavity and must therefore use their flagella to actively swim to and colonize the protective mucus and lining of the stomach. Researchers have discovered a novel protein, called ChePep, that the bacterium requires to swim properly.

Although H. pylori lacking ChePep have normal looking flagella and are mobile, when they swim they have a slight defect that can cause them to go backwards. If they cannot swim away from the acid and into the protective lining of the stomach, they die.

While ChePep is not unique to H. pylori it is unique to the class Epsilonproteobacteria, which includes the foodborne pathogen Campylobacter jejuni and the deep sea hydrothermal vent inhabitant Caminibacter mediatlanticus.


Same Conditions, Different Outcome in Fungal Infection

Cryptococcus neoformans is a life-threatening human fungal pathogen that is responsible for an estimated 1 million cases of meningitis each year, primarily in HIV-infected and other immunocompromised patients. Interaction with immune cells called macrophages is a key step in whether it causes disease. Until now, the interactions between C. neoformans and host cells have mostly been studied using reference or mutant strains of the pathogen and few studies describe the effects of C. neoformans diversity on infections.

Researchers have developed a flow cytometry assay to study the dynamics of macrophage-C. neoformans interactions. Using several different clinical isolates of C. neoformans, they have discovered that under the same experimental conditions, clinical isolates behave differently and these differences could well have important effects for better or worse on outcomes for patients.

Contact: Jim Sliwa
American Society for Microbiology

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