Mechanism Behind Cystine-Tellurite Blood Agar
FACT: Potassium tellurite (K2TeO3) inhibits the growth of gram-negative bacteria and most of the upper respiratory tract normal flora.
Oxyanions of tellurium, like tellurite (TeO32-), are highly toxic for most eukaryotic and prokaryotic organisms. Known for its antimicrobial properties, potassium tellurite has been used in selective media for the isolation of a number of naturally tellurite-resistant bacterial species such as the C. diphtheriae. These tellurite-resistant bacteria reduce tellurite to its elemental less toxic form tellurium Te0 intracellularly. The result is the accumulation of black deposits inside the cell is due to either internal or periplasmic accumulation of Te.
Tellurite toxicity results from its ability to act as a strong oxidizing agent over a variety of cell components. Tellurite could exert its toxicity through intracellular generation of reactive oxygen species (ROS). Tellurite inhibits the cellular response to oxidative stresses. To inhibit the growth of most normal bacterial inhabitants of the upper respiratory tract, including most species of Streptococcus and Staphylococcus, is to inhibit the growth of aerobic organisms through the presence of oxygen and high concentration of tellurite.
Reactive oxygen species compounds such as hydrogen peroxide (H2O2), superoxide anion (O2-) and hydroxyl redical (OH-) are natural byproducts of the normal metabolism of oxygen that can be formed by exposure of cells to free-radical generating molecules like metals and metalloids. ROS compounds are generally very small molecules and are highly reactive due to the presence of unpaired valence shell electrons. Increase of ROS levels dramatically due to the action of tellurite will result in significant damage to cell structures. This situation is known as oxidative stress.
Generally, harmful effects of reactive oxygen species on the cell are most often:
1. damage of DNA
2. oxidations of polydesaturated fatty acids in lipids
3. oxidations of amino
Oxyanions of tellurium, like tellurite (TeO32-), are highly toxic for most eukaryotic and prokaryotic organisms. Known for its antimicrobial properties, potassium tellurite has been used in selective media for the isolation of a number of naturally tellurite-resistant bacterial species such as the C. diphtheriae. These tellurite-resistant bacteria reduce tellurite to its elemental less toxic form tellurium Te0 intracellularly. The result is the accumulation of black deposits inside the cell is due to either internal or periplasmic accumulation of Te.
Tellurite toxicity results from its ability to act as a strong oxidizing agent over a variety of cell components. Tellurite could exert its toxicity through intracellular generation of reactive oxygen species (ROS). Tellurite inhibits the cellular response to oxidative stresses. To inhibit the growth of most normal bacterial inhabitants of the upper respiratory tract, including most species of Streptococcus and Staphylococcus, is to inhibit the growth of aerobic organisms through the presence of oxygen and high concentration of tellurite.
Reactive oxygen species compounds such as hydrogen peroxide (H2O2), superoxide anion (O2-) and hydroxyl redical (OH-) are natural byproducts of the normal metabolism of oxygen that can be formed by exposure of cells to free-radical generating molecules like metals and metalloids. ROS compounds are generally very small molecules and are highly reactive due to the presence of unpaired valence shell electrons. Increase of ROS levels dramatically due to the action of tellurite will result in significant damage to cell structures. This situation is known as oxidative stress.
Generally, harmful effects of reactive oxygen species on the cell are most often:
1. damage of DNA
2. oxidations of polydesaturated fatty acids in lipids
3. oxidations of amino
References: Effects of the Metalloid Oxyanion Tellurite (TeO32−) on Growth Characteristics of the Phototrophic Bacterium Rhodobacter capsulatus; Roberto Borghese, Francesca Borsetti,1 Paola Foladori,2 Giuliano Ziglio, and Davide Zannoni Dipartimento di Biologia, Università di Bologna, Bologna,1 Dipartimento di Ingegneria Civile e Ambientale, Università di Trento, Trento, Italy Tellurite-mediated thiol oxidation in Escherichia coli; Raymond J. Turner, Joel H. Weiner and Diane E. Taylor Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N41 Koneman’s Color Atlas and Textbook of Diagnostic Microbiology; Washington C. Winn, William M. Janda, Paul C. Schrekenberger, Gary W. Procop, Gail L. Woolds, 2005, Lippincott Williams & Wilkins p. 1478 Bacterial Toxicity of Potassium Tellurite http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0000211;jsessionid=47C149456B7896F8CEC642A0E4EAABEC Wikipedia: Reactive Oxygen Species http://en.wikipedia.org/wiki/Reactive_oxygen_species