Investigation of antimicrobial resistance in wild-type and stress-resistant Saccharomyces cerevisiae strains

Abstract

Fungi are organisms that live in various habitats like air, soil and water. Some species live as symbionts and some are parasites. Fungi kingdom consists of mushrooms, molds and yeasts. They all contain rigid cell walls. Yeast are spread worldwide, they are mostly in the phylum ascomycota, and only a few are within the phylum Basidiomycota. There is a high number of economically important types of ascomycete yeasts. These types are commonly used in bread, wine, and beer production; and are selected from Saccharomyces cerevisiae strains. Saccharomyces cerevisiae is a eukaryotic unicellular microorganism. It has a completely sequenced compact genome which makes it a suitable microorganism for easy manipulation of the genome and also ease of cultivation. In this study, ethanol-resistant, coniferyl aldehyde-resistant, caffeine-resistant, propolis-resistant and antimycin-resistant mutant S. cerevisiae strains which were previously obtained by inverse metabolic engineering strategy, were analyzed against different antimicrobials and possible relations between resistance to those antimicrobials were investigated. For this analysis, spot assay method was applied to reference strain (905) and mutant strains under respirative and fermentative conditions against rapamycin, erythromycin, kanamycin and antimycin-A antimicrobials. Antibiotics are generally known and referred to as a subset of anti-infective agents which are derived from bacterial or fungal sources that are used to treat bacterial infections. Antibiotics are generally used medically to treat or prevent bacterial infections. Most antibiotics inhibit the replication or completely kill bacteria. The name 'antimicrobial' is a general term for any compound that inhibits some vital functions or kills microorganisms including chemicals such as antibiotics, antifungal agents, antivirals, and antiseptics. Fungi and viruses may also pose some risks to humans and are targeted by antifungals and antivirals, respectively. Rapamycin is a macrocyclic antibiotic. It is produced by the soil bacterium Streptomyces hygroscopicus found on Easter Island soil. Rapamycin was discovered as a potent antifungal agent, but initially, it exhibited an undesirable and immunosuppressive effect, leading to its development as a clinically useful drug. Rapamycin is the inhibitor of Target of Rapamycin (TOR) pathway. This pathway has important roles such as nutrient sensing, chronological aging, apoptosis and energy metabolism. There is a recent discovery which states that the mTOR inhibitor rapamycin can extend the lifespan of mammals which has created great excitement, as it represents the first demonstration of the pharmacological extension of maximum life in a mammalian species. Since then, rapamycin effects on the lifespan of mammals have been confirmed by some additional studies. Kanamycin is mostly known and referred as kanamycin (A). It is an aminoglycoside bactericidal antibiotic which is found in oral, intravenous, and intramuscular forms. It is used to treat and cure a wide range of infections. Kanamycin is isolated from the bacterium Streptomyces kanamyceticus, and its mostly and commonly used form is kanamycin sulfate. Aminoglycosides function by binding to the bacterial 30S ribosomal subunit and causing misreading of t-RNA. By this way, the bacterium cannot synthesize the proteins vital for bacterial growth. Aminoglycosides are generally used against infections of aerobic, gram-negative bacteria such as Pseudomonas, Acinetobacter, and Enterobacter. Additionally, some mycobacteria are susceptible to aminoglycosides, including bacteria that cause tuberculosis. Infections caused by gram-positive bacteria can also be treated with aminoglycosides, but other antibiotics are more potent and less harmful to the host. Erythromycin is a bacteriostatic macrolide antibiotic produced by Streptomyces erythreus. By binding to the 50S ribosomal subunit, it inhibits protein synthesis. The binding to the 50S ribosomal subunit inhibits peptidyl transferase activity and interferes with the translocation of amino acids during the cycling and coupling of proteins. Erythromycin is released from the bacterial cell membrane and is reversibly attached to the 50S subunit of the bacterial ribosome. This prevents bacterial protein synthesis. Depending on the concentration of the drug, erythromycin may exhibit bacteriostatic or bactericidal action in the infection site and the sensitivity of the related organism. Additionally, erythromycin may enhance the actions of other drugs by the inhibition of microsomal metabolism, leading to toxicity of these other medications. Erythromycin is available in the form of different esters, including erythromycin estolate, erythromycin lactobionate, erythromycin ethylsuccinate, and erythromycin gluceptate. Antimycin-A is an antifungal produced by Streptomyces species. It is the mitochondrial complex III inhibitor. Antimycin binds closely to a pocket in 1 of 5 of the major electron transport proteins. Antimycin binds at the stage where ubiquinol, referred to as (coenzyme Q,) which usually binds to produce electrons to the level of (O2) that is bound to a close iron-containing enzyme. This explains why the electron transporter is blocked at some stages, the bound oxygen is exchanged to superoxide, a very reactive form of oxygen. Antimycin interacts specifically with the complex system of protein structures related to the electron movement. Biochemists make use of this specific binding of antimycin to avert the electron flow and to investigate the chemical details of aerobic respiration. With these investigations, significant information has been revealed about how antimycin adds at the enzyme level, down to the molecular level and the specifics on how the side chains on the antimycin can impact and influence the electron movement at the protein stage. Antimycin is an active ingredient in Fintrol®, a registered product, used as an industrial agent (pesticide). As a result of the antifungal properties, it has been demanded for commercial applications in agriculture. Antimycin is highly toxic to fish species. However, it is used in many fisheries. It has also been used as a commercial toxic agent to get rid of the unwanted fish species in catfish farms. Cross resistance analysis revealed that all mutant strains showed similar behavior against erythromycin and antimycin-A stress. Additionally, under fermentative conditions, only rapamycin affects the growth of the yeast. The aim of this study was to determine the antimicrobial resistances of some stress-resistant S. cerevisiae mutant strains and to identify possible relationships between cross-resistances to different antimicrobials and a variety of stress types. The results could be useful for future research on antibiotics and antifungals resistance.