Multidrug-Resistant Tuberculosis (MDR-TB): Mycobacterium tuberculosis

Multidrug-Resistant Tuberculosis (MDR-TB): Mycobacterium tuberculosis


Professor Dave here, let’s talk tuberculosis. Consumption. The King’s evil. Scrofula. Pott’s disease. What do these terms have in common? They all refer to tuberculosis. Believe it or not, tuberculosis has inspired
poets, artists, novelists, and composers over the years. While the term “tuberculosis” was coined
by Johann Schonlein in 1834, scholars estimate that the disease has been around for as long
as three million years. Tuberculosis, or TB, often presents like the
flu, with symptoms such as chills, vomiting, weakness, night sweats, a persistent cough,
sore throat, or fever. Literally anyone can get TB, and a cough lasting
three weeks or longer is often a warning sign. So what causes it? TB is caused by Mycobacterium tuberculosis,
a bacteria that is able to establish a lifelong infection in a host. These bacteria are weakly gram-positive aerobic rods. Their cell walls are rich with lipids, making
them highly resistant to detergents, antibacterial antibiotics, and disinfectants. M. tuberculosis enter the respiratory airways
and get taken up into immune cells, where they’re able to evade being killed by the
immune system, continuing to replicate and spread. In some cases, the bacteria can spread to
lymph nodes, through the bloodstream, or to other tissues such as bone marrow, spleen,
kidneys, or even the central nervous system. Multidrug resistant TB, which is often abbreviated
to MDR-TB is a particular type of drug resistant TB, meaning that the TB bacteria that a person
is infected with are resistant to two of the most important TB drugs, isoniazid, or INH,
and rifampicin, or RMP. The bacteria that cause TB spread through
the air from person to person, through talking, singing, or coughing. A person can breathe in these bacteria from
another person’s cough and become infected. In fact, these bacteria can float in the air
for several hours, depending on the environment. It’s worth mentioning that TB is NOT spread
by sharing food, shaking hands, kissing, or sharing toothbrushes. There are two types of TB conditions: latent
TB and TB disease. As we discussed in an earlier tutorial, a
latent infection means that the bacteria live in the body without making a person sick. In the majority of people who breathe in TB
and become infected, their body is able to fight off the infection and stop it from growing. Those with a latent infection don’t have
symptoms, don’t feel sick, and most importantly, can’t spread TB to anyone else. However, if the bacteria become active and
start multiplying in the body, that person will go from having a latent TB infection
to being sick with TB disease. Those with TB disease typically do show symptoms
and can spread TB bacteria to others. Like with all diseases that are treated with
antibiotics, it is very important that people who have TB disease finish the full treatment
of antibiotics, taking great care to use the drugs as directed. If they stop taking the drugs too soon because
they feel better, they can very easily become sick again, but this time, the bacteria are
likely to have developed resistance to those drugs, an example of natural selection in action. Drug-resistant TB is much harder, and way
more expensive to treat. Multidrug resistant TB has developed largely
due to misuse or mismanagement of TB drugs, as in when the wrong treatment is prescribed,
meaning the wrong dose, wrong length, or wrong drug altogether, when patients don’t take
their full course of drugs, or when the drug supply runs out or the drugs are of poor quality. “XDR-TB” is the abbreviation for extensively
drug-resistant tuberculosis, which means resistant to at least four of the main anti-TB drugs. To diagnose TB, doctors use either a TB skin
test, called a TST, or a TB blood test. A positive TB skin or blood test simply means
that the person has been infected with TB, and does not specify whether the person has
latent TB or TB disease. Often, a chest x-ray or sputum sample, which
means saliva, can help with diagnosis. There is a vaccine to prevent TB disease that
is used specifically in some countries to prevent severe TB in children, though it is
not generally recommended for adults. So there’s a bit of information on tuberculosis,
and an important lesson on proper antibiotic use.