Which of the following bacteria could be responsible for severe infections like blood poisoning?

Streptococci are a type of bacteria known for causing a variety of infections, some of which can escalate to severe conditions such as blood poisoning, also referred to as bacteremia. This group of bacteria includes Streptococcus pyogenes, which is responsible for illnesses ranging from mild skin infections to life-threatening conditions like necrotizing fasciitis and sepsis. The ability of streptococci to invade tissues and enter the bloodstream makes them particularly dangerous under certain circumstances.

In contrast, the other options present organisms less commonly linked to blood poisoning. Diplococci, which typically include species like Neisseria, are associated with specific infections such as gonorrhea and meningitis, rather than broad outbreaks like blood poisoning. Viruses and fungi, while they can cause serious infections, are not classified as bacteria and generally do not lead to blood poisoning in the same way that streptococci do. Therefore, streptococci's pathogenic potential and historical links to severe systemic infections firmly establish them as the correct answer in this context.