The Staphylococcus aureus



Staphylococcus belongs to the Bacterial family Staphylococcaceae, along with 3 other divisions, Gamella, Micrococcus and Salinicoccus, which can cause numerous amounts of diseases as the bacteria infects various tissues of the body. There are over 30 different types of Staphylococci which can infect a human body. These include Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus citreus, and many more. However, the most common type is Staphylococcus aureus and is the main focus of this review; though, some comparisons will be made with other bacterial family. This review also includes some sample medium to help culture and test Staphylococcus aureus, and their characteristics are also described to distinguish Staphylococcus bacterium from the others.


Staphylococcus aureus should always be regarded as a potential pathogen when compared to non-pathogenic Staphylococcus. As outside the hospital environment, Staphylococcus epidermidis may sometimes take on a protective role as normal flora in humans. Other types of Staphylococcus which are harmful to humans include the MRSA - Methicillin resistant Staphylococcus aureus. MRSA are types of Staphylococcus aureus which are resistant to methicillin and related antibiotics, for example penicillin. Some MRSA are resistant to all antibiotics, except for one or two, including the VRSA (Vancomycin).

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There are two types of MRSA, HA-MRSA and CA-MRSA. HA-MRSA which stands for Hospital Associated MRSA happens most commonly amongst patients who have recently had an operation, recently hospitalized or weaker patients with lower immune systems. The second type, CA-MRSA stands for Community Associated MRSA, are community wise MRSA. This occurs to healthy people who have not been hospitalized recently nor have any medical surgeries. These pus-filled lesions and boils may appear to be less fatal than that of the HA-MRSA symptoms by it spreads rapidly and can affect vital organs leading to serious illness, pneumonia.

Staphylococci can be prevented in several ways, although no vaccine is available. Careful hand washing can avoid close skin contact with infected individuals, and careful cleaning of skin scrapes, wounds and cuts can reduce the possibility of having the Staphylococcus infection.

Environmental niche

Staphylococcus aureus can be found on multiple sites of the skin and moist surfaces of carriers, however the main source of Staphylococci is thought to be in the anterior nares. This is because keratinized epidermis with hairs, sweat glands and sebaceous glands line the interior of the nose. Although the bacteria alone on the skin does not cause any harm, when the wounds are not treated properly, this can then lead to infections ranging from minor effects such as boils and styes to more serious infections such as pneumonia, meningitis and urinary tract infections and finally deep-seated infects, endocarditis.

Staphylococcus aureus is also a major cause of surgical wound infections as it dominates the sutures, which makes the infection harder to restrain. Not only does Staphylococcus aureus cause major infections in the hospital, it also causes food poisoning to humans by releasing enterotoxins, which are protein toxins that are released by microorganisms in the intestine, into what they eat which causes diarrhea and vomiting. The release of superantigen into the blood stream can also trigger toxic shock syndrome if the host lacks specific antibodies.

Staphylococcus can also be found on various parts of the bodies on animals and poultry. One of the major pathogens causing mastitis in the cattle is Staphylococcus aureus. Staphylococcus aureus holds on well, compared to other species of bacteria to the bovine mammary epithelium, especially if the cells are located higher up in the glands. Staphylococci only attaches to the dome-shaped, hexagonal cells that seem competent of secretion. As stated earlier, Staphylococci also have the potential to invade the blood stream as they encounter with endothelial and mesothelial cells. Staphylococcus aureus will stick to these cellular surfaces and they may even enter the cells, and then release superantigens which can cause the host to become sick and infected.


Staphylococci are gram-positive, facultative anaerobes, spherical in shape, around 1 micrometer in diameter that grow by aerobic respiration which occurs in microscopic clusters that bears resemblance to a bunch of grapes. On rich medium, Staphylococcus aureus forms a large yellow colony. Staphylococcus aureus can grow at a temperature range of 15? ~ 45?, and 15% of NaCl concentration. Some other characteristics that help distinguish between Staphylococcus aureus and Micrococci are the large amounts of glycine contained in the cell wall peptidoglycan of Staphylococcus aureus. This is not present in the cell walls. Staphylococci also produce a special type of lactic acid from glucose under anaerobic conditions that are highly valuable in assisting the differentiating of Staphylococci along with its cell wall composition.

Growth Media

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Isolating Staphylococci could be catered by collecting samples by swabbing the site carrying the bacteria, either on the human skin or the lining of the mucus membrane with a sterile cotton swab. Immediately after collecting the sample, inoculate the entire surface of a standard isolation agar plate. The plate will then be incubated for 4 days at around 34? and then examined.

Isolation medium which could be used is "P agar", or "Mannitol Salt agar". According to [Isolation and Characterization of Staphylococci], the medium and culturing techniques used were similar to that of isolating Micrococci. This is because both Staphylococci and Micrococci can be found on the human skin, and by using the same medium, we could try differentiating them through their distinctive characteristics.

"P agar" consists of the following:

Blood agar (sheep or horse) could be used as a nutrient bas to further distinguish Staphylococcus aureus species as the strain shows certain haemolysis. However, this requires special expertise to recognize the bacteria.

When testing for Staphylococcus aureus, the most commonly test used is the coagulase test. When differentiated, Staphylococcus aureus produces a positive result, whereas Staphylococcus epidermidis gives a negative result. The positive results show that Staphylococcus aureus is a pathogenic compared to Staphylococcus epidermidis. The coagulase test can be carried out by combining the human or rabbit plasma with a sample of a young culture of organisms mixed either in a tube or on a glass slide. With the use of the coagulase test, clot forms from the fibrinolytic enzymes produced by some Staphylococcus aureus strains. This indicates a positive result. Other examples for testing the presence of Staphylococcus aureus include DNase, thermostable nuclease and fermentation of mannitol.


Staphylococcus aureus infection can occur to anyone. Out of all infections, skin infections are the most common. People with cuts or scrapes are more likely to contract Staphylococcus. The best way in preventing the infection is to wash hands regularly and keep wounds clean. The infection can be treated with antibiotics, but some Staphylococcus bacteria as previously discussed are antibiotic resistant. This includes the HA-MRSA and the CA-MRSA. Different types of tests were discussed that could be used to isolate Staphylococcus aureus. The most commonly used test is called coagulase test. If distinguishing without a microscope, catalase test would be used, because if the bacteria is catalase positive (Staphylococcus aureus), bubbles will form straight after hydrogen peroxide is added to the agar. This test, however, will not be suitable for use on blood agar, as blood itself contains catalase. Staphylococcus may appear everywhere on human skin and mucosal surfaces, but with correct precaution, infections can still be prevented.


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