Which organism's optimal growth temperature is at 28°C?

The organism that exhibits optimal growth at 28°C is Yersinia pestis, which is the causative agent of plague. While Yersinia pestis can grow at a range of temperatures, its optimal growth occurs around this temperature, especially in the context of environmental conditions. It is worth noting that Yersinia pestis is a bacterium that is often associated with colder environments, which aligns with its optimal growth temperature being lower compared to many pathogenic bacteria that thrive at human body temperature (37°C).

The other options, such as Shigella, Moraxella catarrhalis, and Salmonella typhi, typically have optimal growth temperatures around human body temperature (37°C) or slightly above, reflecting their adaptation to live within the human host rather than in cooler environments. This understanding of the growth conditions for these pathogens is crucial in clinical microbiology for both culturing and identifying these organisms during laboratory work.