Staphylococcus Aureus: Composition and Function

Staphylococcus was first uncovered in 1880 by Alexander Ogston. Currently, more than 30 different species of the genus has been identified. The name "Staphylococcus" was produced from Greek, with the prefix "Staphylo" discussing "bunches of grapes" and the suffix "coccus" discussing "granule" (16). As the meanings suggest, bacterias from Staphylococcus are circular-shaped and their arrangement resembles bunches of grapes when noticed under a microscope. Typically, a Staphylococcus has a diameter of approximately 1μm (21).

The bacterial genus, Staphylococcus, will be isolated and recognized in this task. This genus has been chosen to review due to its abundance on your skin of mammals and the pathogenic characteristics of 1 of its member, Staphylococcus aureus. Apart from skin attacks, Staphylococcus aureus could mutate to create Methicillin-resistant Staphylococcus aureus (MRSA), which ultimately shows resistance to antibiotics. In both circumstances, these give rise to medical implications. Furthermore, the distinctive features of Staphylococcus aureus have increased the ease to isolate and identify it from other kinds in the genus via culturing and biochemical assessments.

The aim of the task is to isolate Staphylococcus aureus from a bundle of pet cat hairs and check its personal information via microscopic evaluation and biochemical assessments. No individuals specimen can be used because of the potential pathogenic property of the bacterium. It really is intended that a genuine culture of pathogenic Staphylococcus aureus is obtained. For the purposes of the project, the value of Staphylococcus aureus to humans, its classification in conditions of morphology and physiological properties, ways of isolation with the use of growth multimedia and the approach of streak plating and identification by biochemical lab tests would be the four goals to be addressed.

Objective 1: Importance of Staphylococcus aureus to humans

The importance of Staphylococcus aureus to humans would be defined by a review of its cell composition, cell physiology and environmental niches, accompanied by the medical implications of Staphylococcus therefore of the properties.

Cell structure

As an associate of the Bacteria site, it is expected that Staphylococcus has bacterial cell structure. Quite simply, it lacks nucleus and membrane-bound organelles. The structural elements in a cell of Staphylococcus should include a cell membrane, cell wall, ribosome and nucleoid (6).

Moreover, being one of the five genera from the category of Staphylococcaceae, Staphylococcus possesses specific mobile properties that are unique to the family. Specifically, it is a cocci and gram-positive bacterium and this signifies that its cell wall is essentially composed of a thick coating of peptidoglycan (21).

In addition to these constructions, Staphylococcus aureus owns some special mobile structures that differentiate it from other kinds in the genus. This consists of the possession of surface protein that help attachment to proteins including the fibronectin and fibrinogen-binding protein involved in blood clotting (3). This cellular property may describe the pathogenic mother nature of Staphylococcus aureus, as infections might be triggered by invasion via wounds.

On the other side, it is useful to notice that Staphylococcus doesn't have flagella and spores (16). In other words, Staphylococcus aureus is non-motile.

Cell physiology

The cell physiology of Staphylococcus addresses heat range, pH and air requirements.

Most Staphylococcus can expand at 45C, but it is acceptable to predict that its best heat for metabolism would be close to the body heat range of humans, which is 37C (5).

Concerning the perfect pH for metabolism, the enzymes in Staphylococcus work best in just a bit alkaline medium, with a pH selection of 7. 4 to 7. 6 (16).

As for air requirement, Staphylococcus is facultative anaerobic (21). Therefore that Staphylococcus can grow regardless of the presence of air, but the occurrence of oxygen would be more favorable.

In the existence of oxygen, Staphylococcus utilizes sugar to carry out cellular respiration to generate energy for metabolism. Oxygen functions the role of your terminal electron acceptor and it is completely reduced to normal water (8).

When air is lacking or absent, Staphylococcus may go through fermentation and lactic acid is the most common product (21). In the process, glucose is changed into substrate pyruvate, accompanied by its binding to the cofactor Nicotinamide Adenine Dinucleotide (NAD+) to produce lactic acid (6).

Moving on the ways Staphylococcus metabolize, as light is not easily available on pores and skin surface and mucous membranes, it is proposed that Staphylococcus obtain energy via organic and natural chemical compounds. Hence it is undoubtedly a chemotroph (21). The facultative anaerobic property of Staphylococcus may lead to a deduction so it utilizes organic and natural carbon as the foundation of electron when air is present. While some Staphylococcus could use reduced kinds of inorganic nitrates to generate electrons, its choice towards an aerobic atmosphere should determine it as an organotroph (21). When involves carbon source, Staphylococcus is a heterotrophy (12). That is to say, it attains its carbon source by usage of organic chemicals such as sucrose for synthesis of metabolites (19). To summarize, Staphylococcus should be one of the people of the microbial group, Chemo-organotrophic heterotrophs.

Environmental niches

The environmental niches of Staphylococcus can be resolved by its interactions with the environment as to where it is found, the kind of relationship it forms with other organisms and its capacity for going through mutation.

Staphylococcus is often on the skin and mucous membranes of animals with steady body temps, including humans (15). Typically, your skin temperatures of humans is about 32C, which is reasonably close to the perfect temperature of 37oC (22). This improves the growth of this microbe on pores and skin. In addition, the salty environment along pores and skin surface because of the production of sweat may also take into account the plethora of Staphylococcus in humans, since its enzymatic activity is best at more alkaline pH (17).

Staphylococcus aureus specifically colonizes in nose cavity, larynx and on your skin surface of humans (2). The colonization of Staphylococcus aureus is principally attained by fibrinogen-binding proteins sticking with the epithelial cells of the humans and so this may format a host-parasitic relationship between Staphylococcus and humans (10).

The relationships of Staphylococcus with the surroundings may also be underlined by mutation, which frequently occurs with Staphylococcus aureus. An example would be Methicillin-resistant Staphylococcus aureus (MRSA), a Staphylococcus aureus that is repellent particularly to the antibiotic, Methicillin (21). The mutation is induced by a modification of the methicillin-resistance gene (mec A) coding for a penicillin-binding necessary protein (4). This brings about failing of antibiotics to treat infections caused by Staphylococcus aureus, which is addressed in the medical implication section.

Medical implications of Staphylococcus

The features just as the cell structure, cell physiology and environmental niche categories of Staphylococcus can create a great variety of medical implications, which presents the importance of the bacterial genus.

Statistics show that Staphylococcus aureus exists in 79% of healthy people (14). Though Staphylococcus may colonize on the skin surface of the web host without causing any harms, its ubiquity can still present various medical issues. The MRSA mentioned previously would be one of the issues associated with Staphylococcus. Apart from methicillin, MRSA could show level of resistance against a great many other antibiotics such as penicillin and amoxicillin (1). The ineffectiveness of existing antibiotics to get rid of MRSA microbe infections has led to fatality, which is usually seen as a the incidence of septic distress and pneumonia (11). An instant increase of MRSA microbe infections has been witnessed over the ages. The pace of hospitalized MRSA infections was only 2% in 1974 but this amount increases drastically to about 40% in 1997 (13). Consequently, this causes fatalities of 19000 in the United Expresses of America annually (11).

As Staphylococcus colonies on skin surfaces and mucous membrane, pores and skin attacks and diseases associated with mucous membranes could be another medical implication. It is known that Staphylococcus aureus could cause Scalded Pores and skin and Toxic Impact syndromes. Moreover, it may cause urinary tract microbe infections and food poisoning (9).

Objective 2: Classification of Staphylococcus

The classification of Staphylococcus can be assessed in terms of its morphology plus some of the physiological properties stated above.


The morphology of Staphylococcus serves as a cocci gram positive bacteria assemble in a cluster, that can be readily witnessed under microscope with the application of gram stain. A purple color would be observed.

The reason for its cluster formation may be explained by its capability of starting binary fission in multiple planes with girl cells remains proximal to each other (16).

Physiological properties

In terms of thermal need, Staphylococcus is classified as a mesophile. Regarding pH requirements, it falls into the group of neutrophile. Moreover, being truly a facultative anaerobe, Staphylococcus is catalase positive and it is generally considered a chemoorganotrophic heterotroph. In addition, Staphylococcus aureus is coagulase positive however, not for other kinds in the genus. The lack of flagella indicates that Staphylococcus is a non-motile bacterium.

Objective 3: Methods of Isolation of Staphylococcus

The ways of isolation of Staphylococcus would include growing in medium accompanied by streak plating.

Growth media

To ensure maximum growth of Staphylococcus colonies, the sample of feline hairs should be enriched in nutrient broth with sodium chloride (NaCl) before plating over a nutrient agar. A nutritional broth normally involves beef draw out and peptone as fuels for growth (21). The temps of incubation should be 37C and the period of incubation should be at least every day (20). This ensures that the Staphylococcus isolated can have sufficient a chance to develop at its perfect temp. The addition of salt allows for a selective medium for Staphylococcus as it mostly grows in salty environment. It also escalates the pH of the medium to give a far more alkaline environment to help growth.

Alternatively, a growth medium can be done with a Mannitol sodium agar (MSA), which involves 7. 5% of NaCl and phenol red as a pH indication. The medium is then incubated at 37C for two days and nights (14). MSA essentially functions as both a selective and differential medium. NaCl selects for saline-favored Staphylococcus and the pH indication differentiates between Staphylococcus aureus and Staphylococcus epidermidis. Differentiation can be illustrated by the fact that Staphylococcus aureus utilizes mannitol in the agar for metabolism, and the generation of acidic product is mentioned by a yellow color. However, this sensation does not apply to Staphylococcus epidermidis (21).

Streak Plating

Following enrichment, Staphylococcus in the medium can be used in an agar dish with nutrient broth and sodium, by employment of aseptic techniques. At the same time, a transfer to an agar plate with only nutritional broth should be performed as a control set-up. That is to guarantee the performance of the selective advertising because other bacteria could increase on the agar plate if the medium had not been create properly.

Afterwards, the plates would be incubated for a week at 37oC for at least a day such as the incubation of test in the nutrient broth. Plating and incubation should be repeated a few times to be sure that the colonies expanded are clean.

Objective 4: Recognition by biochemical tests

The identity of Staphylococcus can't be confirmed by undertaking the gram reaction alone due to the fact a great variety of bacterias from other genus could also show gram positive reaction. Therefore, some biochemical lab tests need to be performed to check that the bacteria isolated is in the genus of Staphylococcus which is of the types Staphylococcus aureus. The catalase, Hugh and Leifson's oxidation fermentation and cogulase testing are thought to be the standard exams for id of Staphylococcus aureus (18). The mechanism of the checks is outlined below.

First of most, as Staphylococcus aureus is facultative anaerobic, it is expected that it includes enzymes to breakdown harmful products generated over the pathways of aerobic respiration. For situations, catalase reduces superoxide radical hydrogen peroxide (H2O2) to air and water, that are less hazardous (8). Therefore colorless gas bubbles can be viewed when H2O2 is put into a colony of Staphylococcus aureus.

Moreover, this property allows the Hugh and Leifson's oxidation fermentation test to be performed. The bacterial test is inoculated in a tube of Hugh & Leifson's medium for five times to create an anaerobic environment (18). As Staphylococcus can experience fermentation in the lack of oxygen, growth can be viewed throughout the pipe. At the same time, it is necessary to implement positive and negative controls in order to verify results. This can be achieved by inoculating bacterias that are known to be fermentative and oxidative respectively in the Hugh & Leifson's medium combined with the test of Staphylococcus aureus.

Furthermore, the identification test between Staphylococcus aureus and other bacteria in the genus would be predicated on its response with coagulase. Staphylococcus aureus commonly coagulates plasma but not for others varieties in the genus (21). To make sure accuracy of the test, it is preferable to test on colonies extracted from culture plates that are recognized to contain coagulase positive Staphylococcus aureus and coagulase negative Staphylococcus epididymis respectively. The previous works as a positive control, while the latter acts as a poor control.


In conclusion, Staphylococcus is a bacterial genus that can pose various medical implications and it can be harvested, isolated and determined predicated on its, environmental niches, morphology, physiological and structural characteristics. The goals of isolating Staphylococcus aureus as a pure culture and identifying by morphology and biochemical assessments can be tackled by an assessment of the four targets as summarized below.

Firstly, it is found on epidermis of pet skins including humans and its ability to metabolize optimally at 37C and at pH of 7. 4-7. 6 or salty environment makes it a potential pathogen to humans. Specifically, the varieties Staphylococcus aureus can result in a great diversity of diseases and the mutated Methicillin-resistant Staphylococcus aureus could be fatal owing to its resistance to many antibiotics.

Secondly, it could be classified in conditions of morphology plus some of the physiological characteristics. Its morphology is gram positive and non-motile cocci bacterias growing in clusters. It is a mesophile, nuetrophile and facultative anaerobe. It really is catalase positive in support of Staphylococcus aureus is coagulase positive. The, electron and carbon resources of Staphylococcus aureus can be described as chemo-organotrophic heterotrophic.

Thirdly, regarding development medium, the test of cat locks should be enriched in a medium of sodium chloride before incubating by using an agar bowl of nutrient broth and salt. In both situations, incubation should be at 37oC for per day. The colonies should be streaked plated several times to remove contaminants in order to ensure culture is 100 % pure. This escalates the efficiency of isolation of Staphylococcus aureus.

Lastly, Staphylococcus aureus can be discovered by the catalase, Hugh & Leifson's oxidation fermentation and coagulase assessments. It is expected that bubbling is noticed as a positive bring about the catalase test. As for the Hugh & Leifson's oxidation fermentation test, development can be observed throughout the tube. In the coagulase test, clumping of plasma sometimes appears as a good result and this differentiates Staphylococcus aureus from other types in the genus. These lab tests establish the personality of Staphylococcus aureus.

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