One Out of Three People Carries Tuberculosis that Has No Clinical Symptom

African scientists have made a headway in grasping drug-resistant Tuberculosis (TB) – a type of TB caused by a persistent TB bacteria. The team of scientists at Stellenbosch University in South Africa, together with colleagues at Imperial College London, found a new way to identify, isolate and target persistent bacteria using a technique that has never before been applied in TB research. This technique will help scientists understand why some bacteria respond to treatment and others become resistant.

The arrival of drug-resistant tuberculosis has significantly complicated global efforts to decrease the scourge of the disease. Each year more than nine million people are infected with TB and another 1.5 million die. But the latest figures show that at least 20% of people diagnosed with the disease have “multiple-drug-resistant” TB. And about 9.7% of these also have “extensively-drug-resistant TB”.

Scientists at the Sokoine University of Agriculture in Tanzania trained rats to detect tuberculosis (TB) in human saliva by smell.

TB is caused by bacteria that attacks the lungs. Most TB treatments target bacteria that actively grow in the body. But a very important subset of bacteria is able to survive treatment. These are known as persistent bacteria.

Though these persistent bacteria only represent a very small proportion of the bacteria that causes TB, failing to get rid of them can have devastating consequences. They are responsible for lengthy drug treatment, and could contribute to drug resistance. They therefore should also be the target of TB therapies.

The challenge with these persistent bacteria is that they are very difficult to isolate. This makes it difficult to study them and therefore difficult to develop drugs to kill them.

How this Bacteria Works

Persistent bacteria plays a particularly important role in latent TB – when bacteria that can cause TB hibernate in the body. Someone with latent TB will not have any clinical symptoms and will therefore not know that he or she has the disease. Latent TB can survive in the body for decades and only flare up when someone’s immune system is compromised.

Latent TB can therefore progress to full-blown disease in people who have compromised immune systems. These are often people who have HIV/AIDS, suffer from malnutrition, are ageing or have a substance-abuse problem. About one-third of the world’s population carries latent TB.

Conventional thinking has held that persistent bacteria are also present in people who have latent TB. These bacteria are thought to either stop growing or are slowly growing, although they still survive in the body.

But emerging research has started to question this assumption on two fronts: Some research shows that proportions of the bacteria continue to grow while others die. Other research argues that the bacteria do not grow. Understanding the bacteria present in latent TB is important to choose the best TB treatments. This is especially important because of the difficulties associated with treating persistent bacteria that can survive treatment.

A New Method to Study Persistent Bacteria

As published on The Conversation Africa, the researchers focus on finding ways to study and target persistent bacteria. They used specific bacteria-associated labels and sophisticated laser-based methods to identify and isolate this bacteria. The technique, known as fluorescence dilution, uses two fluorescent proteins to label the bacteria. One protein tracks live bacteria and the other measures its growth. As explained by the researchers the technique can best be described as using “micro-tweezers” to physically pick out the slow-growing bacteria from the rest. This enabled them to find the hard-to-identify persistent bacteria.

They were able to do this by applying the same approach that’s been used to isolate the bacteria that causes food poisoning, Salmonella. This involves subjecting the bacteria to conditions that come closest to those found in the body as opposed to conditions in the laboratory.

Using this technique, they found that when bacteria entered a specific type of white blood cell, a population of non- or slowly-growing persistent bacteria appeared. White blood cells play a critical role in defending the body against invading bacteria so in the lab the researchers used white blood cells to mimic the environment found in the body.

They found out that the numbers of persistent bacteria increase by being inside white blood cells. This means that the host’s own defences can help the bacteria to survive TB treatment.\

Hope for the Future

These are only the first steps, but this technique offers unique opportunities to deepen scientists’ understanding of why and how the body’s response to TB treatment results in drug resistance.

Scientists can now, for example, begin to study what drives bacteria into a latent state. Once this is understood, it will be possible to begin designing drugs that better manage latent TB. Importantly, this could help decrease the amount of time it takes to treat TB as well as minimise drug resistance.

Source: The Conversation Africa


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