Question

Which of the following statements is correct? A. Streptococci are catalase positive. B. Growth of Streptococcus pneumoniae is not sensitive to optochin. C. Streptococcus pyogenes is highly sensitive to bacitracin. D. Streptococci are obligate anaerobes. E. Enterococcus faecalis is \(\beta\)-hemolytic.

Short answer

Option C: Streptococcus pyogenes is highly sensitive to bacitracin, is the correct statement.

Step-by-step solution

Evaluate Options

Each statement should be assessed separately for its truthfulness.

Evaluate Option A

Streptococci are, in general, catalase-negative, thus this statement is incorrect.

Evaluate Option B

Streptococcus pneumoniae is sensitive to optochin, so this statement is also not correct.

Evaluate Option C

Streptococcus pyogenes is indeed highly sensitive to bacitracin, rendering this statement to be true.

Evaluate Option D

Streptococci are facultative anaerobes, not obligate ones. Thus, this statement is also false.

Evaluate Option E

Enterococcus faecalis usually displays \(\gamma\)-hemolysis, not \(\beta\)-hemolysis. Therefore, this statement is false as well.

Key concepts

Catalase Test in Microbiology

The catalase test is a straightforward yet vital assay in microbiology used to identify bacteria that produce an enzyme called catalase. This enzyme breaks down hydrogen peroxide into water and oxygen, an essential function for bacterial survival in human tissues where hydrogen peroxide may be present due to the immune response.

The test is simple: a sample of bacteria is exposed to hydrogen peroxide, and if bubbles of oxygen are observed, the test is positive, indicating the presence of catalase. In the context of Streptococcus bacteria, it's important to note that they are generally catalase-negative, as opposed to Staphylococcus bacteria, which are catalase-positive. The absence of bubble formation in the test with Streptococcus aligns with our step-by-step solution indicating that statement A in the exercise is incorrect.

Antibiotic Sensitivity

Antibiotic sensitivity is a measure of how susceptible a bacterium is to various antibiotics. It determines the efficacy of different antibiotics on bacterial strains and guides clinicians in prescribing the appropriate treatment for infections.

Sensitivity is examined using tests such as the disc diffusion method, where antibiotic-impregnated discs are placed on a bacterial culture, and the zones of inhibition, where bacteria do not grow around the discs, are measured. In the exercise, the antibiotic sensitivity of Streptococcus pyogenes to bacitracin (statement C) is acknowledged to be high, indicating that this type of Streptococcus can be effectively treated with bacitracin. Contrastingly, Streptococcus pneumoniae's sensitivity to optochin (statement B) is also accurate as it can be used to distinguish this species from other alpha-hemolytic streptococci.

Hemolysis Types

In microbiology, hemolysis refers to the breakdown of red blood cells and the release of hemoglobin, which can be induced by certain bacterial enzymes. The types of hemolysis observed are commonly classified as \(\alpha\), \(\beta\), or \(\gamma\)-hemolysis.

• Alpha (\(\alpha\)) hemolysis is characterized by a partial breakdown of red blood cells, resulting in a greenish discoloration on agar due to hemoglobin oxidation.
• Beta (\(\beta\)) hemolysis is a complete lysis of red cells, leading to a clear zone around the bacterial colony on the agar plate.
• Gamma (\(\gamma\)) hemolysis is actually non-hemolysis, with no change to the agar or hemoglobin.

In the original exercise, statement E incorrectly describes Enterococcus faecalis as \(\beta\)-hemolytic, when it typically displays \(\gamma\)-hemolysis showing no hemolysis on blood agar plates, aligning with our solution that corrects this statement.