The secret of the resistance of a bacterium against different antibiotics

Bacteria resistant to antimicrobial drugs are a growing public health problem, especially in settings such as hospitals. Among these bacteria, the genus Acinetobacter harbors different species that escape multiple drugs. That is why it is included in the ESKAPE pathogenic group, a series of bacterial species against which the World Health Organization estimates that there is an urgent need to obtain new effective antibiotics, since together they cause 80% of the deaths caused due to infections due to antibiotic-resistant pathogens.

Acinetobacter pittii (A. pittii), a pathogenic bacterium that spreads in hospital settings and often causes catheter-associated bloodstream infections, harbors different genes related to resistance to beta-lactam antibiotics, the most widely used group of antimicrobials, as well as point mutations that seem to be also linked to resistance to colistin, an antibiotic considered to be a “last resort”. This has been described by a study led by a team from the Center for Biomedical Research in the Infectious Diseases Network (CIBERINFEC) in Spain and other institutions inside and outside the country.

“Within this family of bacteria, A. baumannii (the most widespread of this group) and A. pittii have managed in relatively few years to go from being mere environmental contaminants to true producers of serious pathologies, in many cases difficult to treat with antibiotics. ”, explains José Ramos Vivas, a researcher at CIBERINFEC and the Universidad Europea del Atlántico de Santander in Spain and one of the main authors of this work. Despite the still low – albeit increasing – prevalence of A. pittii in hospitals, there is some concern that these strains with resistance determinants may spread as much or more than more problematic species such as their relative A. baumannii. In addition, “these bacteria are difficult to eradicate from hospital environments due to their ability to survive in stressful conditions, also acting as a reservoir of antimicrobial resistance genes in clinical facilities that could easily spread to other pathogens”, warns the researcher.

Therefore, it is important to find out how exactly these species have acquired the characteristics that allow their dispersion and survival in the hospital environment, as well as to find out what are the reasons why they easily recruit components in their genomes that help them resist different treatments. antibiotics. To advance this knowledge, this research group focused on analyzing the genomic characteristics and the determinants of resistance to antimicrobials in five strains of A. pittii that were isolated at the Marqués de Valdecilla University Hospital (Santander).

A large number of mobile elements that can carry resistance determinants are detected in these genomes. These are, for example, genomic islands (one of the main genetic mechanisms of intercellular transfer, by which bacteria that cause nosocomial infections acquire multi-resistance profiles) and transposons (DNA sequences that can move self-sufficiently to different parts of a cell’s genome and cause mutations in the DNA of the genome). “Both the new acquisition and the dissemination of antimicrobial resistance genes are mainly due to the role of these mobile genetic elements, which can move some sequences in the same bacterium (intracellular DNA) or to a new cell through horizontal transfer of genes (intercellular DNA)”, points out María Lázaro, a researcher at the Institute of Agrobiotechnology of the CSIC in Navarra and also co-author of the study.

From left to right: Itziar Chapartegui González, María Lázaro Díez and José Ramos Vivas. (Photos: CIBERINFEC)

Using different bioinformatic programs, this team has been able to define how, as occurs in A. baumannii, different strains of the A. pittii species already harbor transposons, genomic islands, and specific determinants of resistance against different antimicrobial compounds in their genomes, such as colistin, an antibiotic of last resort. “The presence mainly of mobile chromosomal genetic elements and plasmids would allow A. pittii to acquire and spread resistance to various antibiotics. This, together with a capacity similar to that of A. baumannii to form biolayers -or biofilms- on different surfaces, could make it difficult to eradicate it from the hospital environment”, explains Itziar Chapartegui, postdoctoral researcher in the Department of Microbiology at the University of Texas in Galveston (United States), and the first signatory of the study.

“Research of this type, where a complete comparison of the genomes between different strains and species is carried out, can help us to better understand their ecology within the hospital environment and thus optimize strategies that can allow the control of their dispersion”, they conclude. researchers.

The study is titled “Genetic Resistance Determinants in Clinical Acinetobacter pittii Genomes.” And it is published in the academic journal Antibiotics. (Source: CIBERINFEC)