Among bacteria of the genus Salmonella, there are many pathogenic species. Salmonella enterica, a Typhi serotype, is known as the causative agent of typhoid, and the remaining representatives are collectively called non-typhoid salmonella. One of them – Salmonella enterica, a serotype of Typhimurium – causes intestinal infections worldwide: in particular, in Central and South Africa, about 3.4 million people suffer from them annually.
Most of the Salmonella typhimurium serotype in Central and South Africa belong to the ST313 group (ST – sequence type, DNA sequence type). In this species, bacteria have long discovered multidrug resistance: they are not affected by first-line antibiotics such as ampicillin, chloramphenicol and sulfamethoxazole. Therefore, clinical guidelines for the treatment of infections caused by non-typhoid salmonella include the following antibiotics: ceftriaxone and ciprofloxacin.
Sandra Van Puyvelde of the Institute of Tropical Medicine in Antwerp and her colleagues took samples of Typhimurium salmonella from patients in three different cities in the Republic of Congo. In 51 samples, scientists found multidrug-resistant bacteria. These bacteria were also insensitive to yet another antibiotic, azithromycin. In addition, they produced broad-spectrum beta-lactamase – an enzyme that allows inactivation of antibiotics from the beta-lactam group, including ceftriaxone. Finally, bacteria had a reduced sensitivity to ciprofloxacin. All this allowed researchers to announce the discovery of a new drug-resistant supermicrobe.
All supermicrobes found by scientists are relatives and belong to the same subline of Salmonella – ST313 II.1. Researchers compiled a phylogenetic tree of ST313 representatives and found that subline II.1 appeared in Congo around 2004.
Since then, representatives of this subline acquired a separate plasmid with antibiotic resistance genes and accumulated single nucleotide substitutions in the genome characteristic of other aggressive representatives of Salmonella enterica. Scientists have found that bacteria also lost the ability to form biofilms and survive on a variety of nutrient media, which indicates their adaptability to life in the human body. In addition, they lost one of the genes that encode the bacterial flagellum protein: it serves as an “alarm” for human immune cells, so without it the bacterium is more difficult to detect and destroy.
Thus, the new supermicrobe, scientists say, is thoroughly prepared for effects on the human body. Currently, researchers have studied bacterial samples from three different cities, and then they will have to check how widely subline II.1 has spread in the Congo or other countries.
Apparently, antibiotic resistance arose long before human colonization with bacteria. However, the use of antibiotics accelerated its spread. For example, antibiotic resistance genes for carbapenems have arrived from India to the Arctic in just a few years.
