The interest in the medical use of plasma is increasing with the consideration of the ever-growing percentage of bacteria that are resistant to antibiotics. Investigators at Ruhr-Universitat Bochum (RUB) have collaborated with colleagues from Kiel to investigate if bacteria may become impervious to plasma, too. The researchers identified 87 genes of the bacterium Escherichia coli, which potentially protect against practical components of plasma. Marco Krewing said that these genes provide insights into the antibacterial mechanism of plasma. Krewing is the lead author of two articles that were published in the Journal of the Royal Society interface this year.
Through the gas that is pumped with energy is where the creation of plasma begins. These days, plasmas are already used against multi-resistant pathogens in clinical applications. The basic instance is to treat chronic wounds. The head of the RUB research group Applied Microbiology, Professor Julia Bandow explained that plasmas provide a complex cocktail of components, many of which act as disinfectants in their own right. UV radiation, electric fields, atomic oxygen, superoxide, nitric oxides, ozone, and excited oxygen or nitrogen affect the pathogens simultaneously, generating considerable stress. Typically the pathogens survive merely several seconds or minutes.
For the researchers to find out whether bacteria may develop resistance against the effects of plasmas, as they do against antibiotics, the team analyzed the entire genome of the model bacterium Escherichia coli, to identify existing protective mechanisms. Julia Bandow explained that resistance means that a genetic change causes the organism to be better adapted to specific environmental conditions. Such characteristics can be passed on from one generation to the next.
For the review, the team used so-called knockout strains of E. coli. These are bacteria that are missing one specific gene in their genome, which contains approximately 4,000 genes. They exposed each mutant to the plasma and monitored if the cells kept proliferating following the exposure.
Marco Krewing noted that they demonstrated that 87 of the knockout strains were more sensitive to plasma treatment than the wild type that has a complete genome. Subsequently, the team analyzed the genes missing in these 87 strains and determined that most of those genes protected bacteria against the effect of hydrogen peroxide, superoxide, and nitric oxide. Julia Bandow elaborated that this means that these plasma components are particularly effective against bacteria. However, it also means that genetic changes that increase the number or activity of the respective gene products are more capable of protecting bacteria from the effect of plasma treatment.
Through the collaboration with a team headed by Professor Ursula Jakob from the University of Michigan in Ann Arbor (USA), the researchers were able to demonstrate that this is indeed the case: the heat shock protein Hsp33, encoded by the hsIOgene, protects E. Coli proteins from aggregation when exposed to oxidative stress. As pointed out by Brandow, during plasma treatment, this protein is activated and protects the other E. Coli proteins, and consequently, the bacterial cell.