STAPHYLOCOCCUS AUREUS

Staphylococcus Aureus

Staphylococcus Aureus

Significance Of Staphylococcus Aureus

Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently part of the skin flora found in the nose and on skin, and in this manner about 20% of the human populations are long-term carriers of S. aureus. S. aureus is the most common species of staphylococci to cause Staph infections. One of the reasons for this is a carotenoid pigment staphyloxanthin that is responsible for the characteristic golden colour of S. aureus colonies. This pigment acts as a virulence factor, with an antioxidant action that helps the microbe evade death by reactive oxygen species used by the host immune system (Bauman, 2008).

Taxonomic Classification

Taxonomy        Name                  Reason placed in specific taxonomy.

Domain:             Bacteria             Bacteria are very small, single-celled organisms that can reproduce quickly

Kingdom:           Eubacteria          Eubacteria are commonly occurring prokaryotes that live in a variety of places

Phylum:             Firmicutes           Firmicutes are gram-positive  (www.earthlife.net)

Class:                Baccilli                Bacilli are rod-shaped  (www.thefreedictionary.com)

Order:                Bacillales      

Family:              Staphylococcaceae   A lot of medically significant pathogens are in this family  (Kauffman, 2006).

Genus:              Staphylococcus        Divide into two planes  (Kauffman, 2006).

Species:            Staphylococcus aureus        Yellow coloring 

Subspecies:       Methicillin-resistant Staphylococcus aureus       Resistant to methicillin an antibiotic 

Organisms can also be placed in a phylogenetic tree.  Here is one example of a phylogenetic tree for MRSA.

The Organism Is Gram + Or Gram-

Staphylococcus aureus organism is a facultative anaerobic Gram-positive coccal bacterium.

Tests To Identify The Organism

Current methods used to identify S. aureus include Gram stain morphology, cell morphology, production of catalase, coagulase production, pigment production, susceptibility to lysostaphin and lysozyme, and anaerobic production of acid from glucose. In addition, there are several commercially available systems that allow strains to be biochemically characterized. Depending upon the type of infection present, an appropriate specimen is obtained accordingly and sent to the laboratory for definitive identification by using biochemical or enzyme-based tests. A Gram stain is first performed to guide the way, which should show typical Gram-positive bacteria, cocci, in clusters.

Second, the isolate is cultured on mannitol salt agar, which is a selective medium with 7-9% NaCl that allows S. aureus to grow, producing yellow-colored colonies as a result of mannitol fermentation and subsequent drop in the medium's pH Furthermore, for differentiation on the species level, catalase (positive for all Staphylococcus species), coagulase (fibrin clot formation, positive for S. aureus), DNAse (zone of clearance on nutrient agar), lipase (a yellow color and rancid odor smell), and phosphatase (a pink color) tests are all done. ...