Which of the following bacterium is associated with toxic shock syndrome?

Toxic shock syndrome is primarily associated with Staphylococcus aureus due to its ability to produce toxic shock syndrome toxin-1 (TSST-1). This toxin can lead to severe illness characterized by rapid onset of fever, rash, and multi-organ failure. Staphylococcus aureus is a common bacterium found on the skin and in the nasal passages, and certain strains can lead to severe infections, particularly when they enter the bloodstream or other sterile areas of the body.

While other bacteria listed can cause various types of infections, they are not primarily linked to toxic shock syndrome like Staphylococcus aureus. For instance, Clostridium perfringens is mainly involved in gas gangrene and food poisoning, Streptococcus pneumoniae typically causes pneumonia and meningitis, and Escherichia coli, particularly certain strains, are known for causing gastrointestinal infections. Thus, Staphylococcus aureus is the most relevant bacterium in the context of toxic shock syndrome.