Question

Staphylococcus aureus is most often associated with being a. coagulase-positive. b. coagulase-negative. c. catalase-negative. d. gram-negative

Short answer

Staphylococcus aureus is most often associated with being coagulase-positive (a).

Step-by-step solution

Identify the Characteristic of Staphylococcus aureus

To solve this exercise, we need to identify the unique enzymatic feature of Staphylococcus aureus among the options given. Staphylococcus aureus is well-known in microbiology for its ability to clot blood plasma due to the presence of the enzyme coagulase.

Eliminate Incorrect Options

Knowing that Staphylococcus aureus possesses the coagulase enzyme, we can eliminate option (b) 'coagulase-negative', (c) 'catalase-negative', and (d) 'gram-negative' because these characteristics are not typically associated with Staphylococcus aureus. Staphylococcus aureus is catalase-positive and gram-positive.

Select the Correct Answer

Since Staphylococcus aureus is known for being coagulase-positive, the correct answer is option (a) 'coagulase-positive'.

Key concepts

Coagulase-Positive Bacteria

Staphylococcus aureus is a prime example of coagulase-positive bacteria, a category defined by the presence of the enzyme coagulase. This particular enzyme is a distinguishing factor and contributory to the pathogenicity of this microorganism. Coagulase works by converting fibrinogen in blood plasma into fibrin, which in turn leads to blood clotting. This is a defense mechanism for the bacteria as it allows them to effectively 'hide' from the immune system within a clotted mass of blood components.

Understanding the significance of coagulase positivity is crucial for diagnostic microbiology. When Staphylococcus aureus is isolated from an infection site, its coagulase-positive characteristic assists clinicians in identifying it and differentiating it from coagulase-negative Staphylococci, which are generally less pathogenic. This information guides the appropriate treatment options for infections caused by these bacteria.

Enzymatic Features of Bacteria

Bacteria express a variety of enzymes that not only facilitate their survival but also play significant roles in their pathogenic profiles. For Staphylococcus aureus, enzymes like coagulase as mentioned earlier, and others such as catalase, are central to its ability to cause diseases. Catalase enables the bacteria to break down hydrogen peroxide, a compound produced by our immune system to kill invading pathogens, into water and oxygen, which are harmless.

The presence of catalase is what makes S. aureus catalase-positive, allowing it to survive in oxygen-rich human tissues. Enzymes are thus a key point in understanding bacterial behavior, contributing to both their survival mechanism and their capability to infect hosts. Knowledge of these enzymatic features is integral in developing both diagnostic tools and treatments against bacterial diseases.

Gram-Positive Bacteria

Gram-positive bacteria like Staphylococcus aureus are characterized by a thick peptidoglycan layer in their cell wall. When subjected to Gram staining, a common technique in microbiology, they retain the crystal violet stain and appear purple under a microscope. This is in contrast to Gram-negative bacteria, which have a thinner peptidoglycan layer and an outer membrane, not retaining the crystal violet and instead appearing red or pink.

Beyond just a laboratory distinction, the Gram status of bacteria has implications for their physiology, antibiotic susceptibility, and the nature of infections they cause. Gram-positive bacteria, without an outer membrane, are usually more susceptible to antibiotics that target peptidoglycan synthesis. Understanding that S. aureus is Gram-positive helps in designing effective treatment strategies, as it narrows down the list of effective antibiotics suitable for eradicating the infection.