This deadly soil bug can reach your brain in a day, end up in spinal cord

In Southeast Asia 50 per cent of the population may be positive for melioidosis; staph and acne bacteria may also end up in the spinal cord
July 11, 2016

B. pseudomallei soil-dwelling bacterium endemic in tropical and subtropical regions worldwide, particularly in Thailand and northern Australia (credit: Wikipedia CC)

Imagine a  deadly bacteria that can be picked up by a simple sniff and can travel to your brain and spinal cord in just 24 hours. Or one that could just be quietly sitting there, waiting for an opportune moment. Or maybe just doing small incremental damage ever day over a lifetime … as you lose the function in your brain incrementally.

That’s the grisly finding (in mice), published in Immunity and Infection this week, of a new study by Australian Griffith University and Bond University scientists.

The pathogenic bacteria Burkholderia pseudomallei, which causes the potentially fatal disease melioidosis, kills 89,000 people around the world each year and is prevalent in northern Australia, where a person with melioidosis has a 20–50 per cent chance of dying once it infects the brain. The bacterium is found in the northern parts of the Northern Territory, including Darwin.

In Southeast Asia 50 per cent of the population may be positive for melioidosis, and in places like Cambodia the mortality rate is as high as 50 per cent.

But for the rest of us, the findings could also lead to discoveries of how the common staphylococcus and acne bacterium also end up in the spinal cord, as well as how chlamydia travels to the brain in Alzheimer’s patients. Or even explain common back problems, which could be where bacteria have infected your bone, causing pain that could be simply treated with antibiotics, according to the researchers.

Tracing the bacteria in mice brains and spinal cords

(Top) A schematic drawing of a mouse brain showing the location of various images. (Bottom) D: A B. pseudomallei rod (arrow) present in trigeminal nerve near the connection between the trigeminal nerve in the brain and the brainstem. (E) B. pseudomallei rod (arrow) with a fluorescent particle (arrow with tail) after the merge between the trigeminal nerve and brainstem. Scale bars in μm. (credit: James A. St John et al./Infection and Immunity)

The olfactory mucosa, located in the nose, is very close to the brain and it has long been known that viruses could reach the brain from the olfactory mucosa. But researchers have not understand exactly how the bacteria traveled to the brain and spinal cord, or just how quickly.

To find out, James St. John, PhD., Head of Griffith’s Clem Jones Centre for Neurobiology and Stem Cell Research, and associates infected mice with B. pseudomallei. They were able to trace the bacteria travels from the nerves in the nasal cavity before moving to the brain stem and then into the spinal cord. (He noted that this could also be a pathway for many other common bacteria.)

“Our latest results represent the first direct demonstration of transit of a bacterium from the olfactory mucosa to the central nervous system (CNS) via the trigeminal nerve; bacteria were found a considerable distance from the olfactory mucosa, in the brain stem, and even more remarkably in the spinal cord,” said professor Ifor Beacham from the Griffith Institute for Glycomics.

Researchers will now work on ways to stimulate supporting cells that could remove the bacteria. St. John said the work was important because the bacteria had the potential to be used as a bioweapon and knowing how to combat it was extremely important.

“Bacteria have been implicated as a major causative agent of some types of back pain. We now need to work out whether the bacteria that cause back pain also can enter the brainstem and spinal cord via the trigeminal nerve,” he added.


Abstract of Burkholderia pseudomallei rapidly infects the brainstem and spinal cord via the trigeminal nerve after intranasal inoculation

Infection with Burkholderia pseudomallei causes melioidosis, a disease with a high mortality rate (20% in Australia and 40% in south-east Asia). Neurological melioidosis is particularly prevalent in northern Australian patients and involves brainstem infection, which can progress to the spinal cord; however, the route by which the bacteria invade the central nervous system (CNS) is unknown. We have previously demonstrated that B. pseudomallei can infect the olfactory and trigeminal nerves within the nasal cavity following intranasal inoculation. As the trigeminal nerve projects into the brainstem, we investigated whether the bacteria could continue along this nerve to penetrate the CNS. After intranasal inoculation of mice, B. pseudomallei caused low-level localised infection within the nasal cavity epithelium, prior to invasion of the trigeminal nerve in small numbers. B. pseudomallei rapidly invaded the trigeminal nerve and crossed the astrocytic barrier to enter the brainstem within 24 hours and then rapidly progressed over 2000 μm into the spinal cord. To rule out that the bacteria used a haematogenous route, we used a capsule-deficient mutant of B. pseudomallei, which does not survive in the blood, and found that it also entered the CNS via the trigeminal nerve. This suggests that the primary route of entry is via the nerves that innervate the nasal cavity. We found that actin-mediated motility could facilitate initial infection of the olfactory epithelium. Thus, we have demonstrated that B. pseudomallei can rapidly infect the brain and spinal cord via the trigeminal nerve branches that innervate the nasal cavity.