Which of the following organisms is known to be susceptible to penicillins?

Streptococcus pneumoniae is known to be susceptible to penicillins due to its cell wall structure, which penicillin targets effectively. The action of penicillin inhibits the synthesis of the bacterial cell wall, leading to cell lysis and death of the organism. Many strains of Streptococcus pneumoniae remain sensitive to penicillins, making it an effective treatment option for infections caused by this bacterium, such as pneumonia and meningitis.

In contrast, Staphylococcus, particularly the methicillin-resistant variant (MRSA), has developed resistance to penicillins and other beta-lactam antibiotics. Pseudomonas aeruginosa also exhibits significant resistance to penicillins, requiring different classes of antibiotics for effective treatment. Thus, while Streptococcus pneumoniae remains susceptible, other options represent organisms that have varying degrees of resistance to penicillin and require alternative therapeutic approaches.