Final answer:
S. pneumoniae is a gram-positive, diplococcal bacterium that is bile soluble and highly sensitive to optochin. It is typically identified by its alpha hemolytic activity on blood agar and definitive identification is via the quellung reaction, but it does not produce catalase. The correct option is (2).
Step-by-step explanation:
Key Characteristics of S. pneumoniae:
Streptococcus pneumoniae, commonly known as pneumococcus, possesses several distinct characteristics used for its identification and classification. S. pneumoniae demonstrates alpha hemolysis on blood agar, appearing as greenish colonies due to the partial lysis of red blood cells. This reaction is indicative of its metabolic activity. These bacteria are gram-positive, and under the microscope, they appear as lancet-shaped diplococci. They can be presumptively identified through their cellular morphology and diplococcal arrangement.
The bacterium is bile soluble, meaning that it can be lysed by the bile or derivatives like sodium deoxycholate. The addition of a 10% sodium deoxycholate solution rapidly destroys S. pneumoniae colonies, which is a unique characteristic feature. Furthermore, it is sensitive to the antibiotic optochin, which is used in laboratory identification; the presence of this antibiotic on a culture plate will inhibit or kill S. pneumoniae. The definitive identification of S. pneumoniae includes the quellung reaction, a serotyping method that detects the bacterium's unique capsular polysaccharides.
Contrary to options given in the question, S. pneumoniae does not produce catalase, which distinguishes it from some other bacteria such as Staphylococcus aureus. Furthermore, S. pneumoniae is not gram-negative; it is a gram-positive organism, another key characteristic that aids in its identification. So, for the provided options, the characteristics that apply to S. pneumoniae are its bile solubility, sensitivity to optochin, and it being gram-positive, while it does not produce catalase.