Every year, about a million people die from bacterial infections resistant to most antibiotics. Among the most common and dangerous antibiotic-resistant bacteria are :

1. Multidrug-resistant strains of Salmonella typhi .

S. typhi is a highly contagious bacterium that causes typhoid fever, a severe disease that affects approximately 21 million people worldwide each year. Approximately 1% of patients die.

The first reports of a multidrug-resistant S. typhi strain, resistant to all oral antibiotics except azithromycin, were reported in Pakistan in 2016. Since then, this S. typhi strain has acquired so-called "extreme antibiotic resistance," meaning resistance to all but two classes of antibiotics. The bacterium can easily acquire resistance to multiple classes of antibiotics by acquiring the relevant genes from other bacteria through horizontal transfer. It's possible that S. typhi is now just one step away from so-called "panresistance"—resistance to all antibiotics without exception—by acquiring a plasmid with the resistance genes.

2. Extremely resistant strains of Mycobacterium tuberculosis .

The tuberculosis pathogen is one of the leading modern killer bacteria, causing 1.7 million deaths annually. The main challenge in treating tuberculosis is that the pathogen parasitizes inside cells, where it is very difficult to reach. Therefore, to eradicate it, the patient must take four different antibiotics sequentially over six months.

According to epidemiologists, 13% of all new tuberculosis cases are multidrug-resistant. For these patients, treatment lasts significantly longer—18-24 months—and involves more expensive medications with a higher risk of side effects. It has now been established that approximately 6% of these cases are caused by extremely resistant strains of M. tuberculosis , and among these patients, the cure rate is only 30%.

3. Pan-resistant strains of Klebsiella pneumonia .

K. pneumoniae is a real scourge of modern hospitals. Normally, this bacterium lives on the skin and in the intestines without causing illness. It becomes a problem for patients with compromised immune systems, those in critical condition, or those exhausted by prolonged illness, surgery, and the like.

In 2013, 8,000 cases of infections caused by multidrug-resistant K. pneumonia were reported in the United States alone. Of patients with K. pneumonia bloodstream infections, 50% died. In 2016, a pandrug-resistant K. pneumonia strain, resistant to 26 available antibiotics, was identified in the United States. A patient infected with this strain died due to a lack of alternative treatment options.

4. Pan-resistant strains of Pseudomonas aeruginosa .

Like K. pneumonia , P. aeruginosa is a dangerous bacterium for weakened people, especially in hospitals.

In the United States, approximately 51,000 hospital-acquired infections caused by P. aeruginosa are reported annually, of which approximately 400 are fatal. Over the past five years, 29 cases of pan-resistant P. aeruginosa infection have been reported in UK hospitals.

P. aeruginosa is one of the leading causes of death among patients with cystic fibrosis. As recently as 2013, more than 42% of patients with cystic fibrosis and chronic P. aeruginosa infection were treated with the antibiotic of last resort, colistin, as the pathogen was resistant to all other antimicrobials.

5. Extremely resistant strains of the gonorrhea pathogen Neisseria gonorrhoeae .

Gonorrhea is a sexually transmitted disease that is usually not fatal, but without proper treatment it can cause serious health consequences, including infertility.

In approximately a third of gonorrhea cases, N. gonorrhoeae is resistant to at least one antibiotic. However, the problem is that doctors are increasingly encountering extremely resistant strains of N. gonorrhoeae , resistant to all antibiotics except one. As mentioned above, bacteria can not only mutate and become resistant to antibiotics themselves, but also easily transmit resistance genes to other bacteria. Thus, the gonorrhea pathogen can soon become resistant to the last antibiotic.

An important step in preventing the spread of antibiotic resistance is the rational use of antibiotics, as well as the widespread use of alternative treatments for bacterial infections, such as bacteriophages. Today, for people infected with pan-resistant bacterial strains, bacteriophages are often the only chance for salvation.