In 1929, Alexander Fleming was working with plates of Staphylococcus aureus. He cultured a plate with this bacteria, but it got contaminated by mold. Instead of throwing it out, like he probably first though to, he noticed that the bacteria did not grow around the mold. He cultured plates of various bacteria strains with a small bit of the mold on the plate as well. Fleming cataloged many bacteria that were and were not affected by Penicillin, but Staphylococcus remained at the vanguard of his research. As predicted by microevolution, the strongest bacteria survived and now S. aureus is the most antibiotic-resistant strain.
S. aureus is a small spherical bacteria about 1 micrometer in diameter that grows in clusters. These colonies grow to be a golden yellow; that is how it got its name. It is a gram positive bacteria that has a microcapsule—it can’t be seen with a normal light microscope. S. aureus are very resilient bacteria that can grow at temperatures between 15 and 45 °C and salt concentrations up to 15%. And now that it is antibiotic resistant, S. aureus is one of the more virulent strains we have today.
This bacteria causes many diseases and is normally found in the nasal passages of infected humans. But it has been found throughout the body including skin lesions. This pathogen has been found to be partially or completely responsible for forms of pneumonia and meningitis. S. aureus is a rather nasty bacteria in the methods it uses to attack cells. It produces three types of toxins: alpha, beta, and leukocidin. Alpha toxin is a small monomer that binds to cell membranes and then polymerized with others to form a small ring through which the cytoplasm leaks out. The beta toxin damages membranes by attacking the lipids, but this is not seen in humans. Leukocidin is consists of eight subunits (4 class F and 4 class S) that form a cross membrane pore and then allow the cell to leak out more than just cytoplasm.
Not only is S. aureus a dangerous killing machine, it is also hard to kill. Besides being antibiotic resistant, it had its own ways of defense before. The most common way the human body rids itself of infection is through leukocytic phagocytosis. But S. aureus produce catalase and carrotenoids which are two enzymes that neutralize superoxide and singlet oxygen; the white blood cells normally use these harmful chemicals to break down foreign bodies. S. aureus also preduces Protein A which reorients marking proteins so white blood cells have a harder time detecting them.
As microbiologists, we prefer to deal with its cousin, Staphylococcus epidermitis. This produces small white colonies and no toxins. This is one of the primary bacteria we use in lab because it grows so well, like S. aureus.
Staphylococcus aureus is a dangerous bacteria. The more we try to combat it with antibacterial and antibiotics, the more resistant is becomes. It is responsible for many infections, but luckily it is rarely fatal. From being the leader in testing antibiotics by Dr. Fleming, it is still the leader in testing antibiotics because other doctors are still trying to find ways to keep it from infecting humans.References:
http://textbookofbacteriology.net/staph.html
http://nobelprize.org/medicine/laureates/1945/fleming-lecture.pdf
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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