Toxin produced by bacteria can be effective in fighting hospital infection

Using computer-based models, a USC research team studied how harmful bacteria survives and determined how to kill it. (Image/iStock)

The bacterium Pseudomonas aeruginosa has been the subject of studies at Cepid Redoxoma, where scientists were able to characterize a biological weapon to fight it. The bacterium can cause infections, especially in the hospital environment – Photo: Pixabay
In hospital infections, one of the most harmful agents to the patient is a bacterium called Pseudomonas aeruginosa . Present in all places – in the soil and in the water -, this microorganism can cause infections, mainly in the hospital environment, being a serious problem for patients with low immunity. At the Research Center for Redox Processes in Biomedicine, Cepid Redoxoma , scientists were able to characterize a kind of “biological weapon” that could combat P. aeruginosa . This is Piocina S8, a bacteriocin produced by P. aeruginosawhich causes the death of cells of the same species during the competition for natural resources. The researchers demonstrated that Piocina S8 has a potent bactericidal activity against antibiotic-resistant P. aeruginosa strains, for which treatment alternatives are scarce. Recently an article was published describing the advances in studies with this bacteriocin in the Journal of Bacteriology .

Professor Luís ES Netto, professor at the USP Biosciences Institute – Photo: Cecília Bastos
According to Professor Luís ES Netto, professor at USP’s Biosciences Institute (IB), today there are several strains of P. aeruginosa that are super-resistant to antibiotics. Therefore, there is an interest in new molecules that can fight the bacteria. Research has been carried out at Redoxoma, under the coordination of Luís Netto, with the participation of scientists from USP’s Institute of Biomedical Sciences (ICB).

The P. aeruginosa is an opportunistic bacterium can colonize a wide variety of hosts. In humans, it is commonly found in burn wounds, urinary tract infections, and obstructive lung disease. It is easily found and disseminated in the hospital environment, being a serious problem for immunocompromised patients.

Therapeutic alternative
Luís Netto describes that, in stressful situations, when there is a competition for nutrients, P. aeruginosa produces the pokokines (bacteriocins of P. aeruginosa ), which are capable of killing other bacteria of the same species. “These molecules can be a therapeutic alternative for the treatment of infections caused by multidrug-resistant strains, such as, for example, those that do not respond to available antibiotics”, explains the researcher to Jornal da USP .

Plate containing pyokines – Photo: Reproduction
Among the different bacteriocins of P. aeruginosa is Piocina S8, which, according to the scientist, has a potent bactericidal activity against multidrug-resistant strains of P. aeruginosa .

Unlike antibiotics, pyokines are proteins and have a restricted spectrum of action, that is, they are capable of killing only P. aeruginosa cells and not an Escherichia coli , for example. This means that the use of pyokines also has the advantage of not interfering with the host’s microbiota, improving the patient’s health and increasing the effectiveness of the treatment.

Biochemical characterization

Researcher Helena Turano – Photo: Personal archive
To understand the mechanism by which this molecule causes cell death during competition for nutrients, Redoxoma researchers carried out the biochemical, microbicidal and structural characterization of Piocina S8. These studies were initiated at ICB, where researcher Helena Turano, first author of the article, completed her doctoral thesis, under the guidance of Professor Nilton Lincopan.

In her doctoral research, Helena was able to identify a bacterial strain (ET02) that produced a pyocin with potent bactericidal activity against multidrug-resistant strains of P. aeruginosa . Through mass spectrometry and sequencing of the genome of the ET02 strain, it was discovered that it was Piocina S8. “This pyocin had only been described by in silico analysis , that is, by computer simulation. It was the first time that it was tested in vivo ”, informs Helena. According to the scientist, there are three types of pyokines, classified according to their structure as R, F and S.

Type R and F pyokines are high molecular weight complexes that resemble bacteriophage tails. Type S pyocins, which were the focus of this research, are low molecular weight molecules, consisting of only two protein subunits or components. The biggest component, as Helena explains, is that it kills the target cells due to an activity that, in the case of Piocina S8, is the breaking of DNA (called DNase activity). The smaller component of pyokine, known as the immune subunit, binds to the larger component and inhibits the DNase activity of pyokine, thus providing protection to the bacterium that produces pyokine.

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After the identification of Piocina S8 in the ICB, the researcher has been carrying out a whole job of characterizing the molecule in the IB during her post-doctoral studies. “It is there that Helena has also been producing Piocina S8 in large quantities and with a high degree of purity”, says Netto.

To better understand the mode of action of Piocina S8, the researchers described the molecular structure of the DNase domain of Piocina S8 associated with the immune subunit by X-ray crystallography, in a resolution that made it possible to visualize many details of the shape of the protein, including its atoms. They also did the biochemical characterization of the molecule, which involved assessing the DNase activity of its cytotoxic domain.

In collaboration with other researchers, who have donated a collection of strains of multidrug-resistant bacteria, Helena plans to carry out pre-clinical trials to find out what is the minimum concentration of Piocina S8 needed to kill the bacteria. The next step will be to perform animal tests. “Unfortunately, we stopped the pandemic, but the idea is that when we can resume normality, it can be done”, warns the researcher to Jornal da USP .

This research shows that there is a possibility that Piocina S8 will become a possible drug for the treatment of bacterial infections. “But we don’t know how to say how long it can take. As far as we know, there is still no description of clinical trials of pokokines in humans ”, explains Helena.

The article Molecular structure and functional analysis of Pseudomonas aeruginosa from pyocin S8 reveals the essential requirement of a glutamate residue in the HNH motif is DNase activity , Helena Turano, Gomes, Renato M. Sunday, Maximilia FS Degenhardt, Cristiano LP Oliveira, Richard C. Garratt, Nilton Lincopan and Luis ES Netto, can be read here .