Which characteristic reflects Serratia marcescens?

Serratia marcescens is known for its ability to produce a bright red pigment called prodigiosin, particularly when grown at room temperature. This pigment gives colonies of Serratia marcescens a distinctive red appearance, which is a key characteristic used to identify this organism in the laboratory. The production of this pigment can vary with temperature and growth conditions, but under optimal conditions, the presence of this vibrant red color is a hallmark of S. marcescens.

In contrast, swarming growth on sheep blood agar (SBA) is more characteristic of other genera, such as Proteus. Typical hemolytic colonies on blood agar plates (BAP) can be observed in various bacteria and are not specific to Serratia marcescens. The appearance of clear colonies on a selective medium like SMAC (Sorbitol-MacConkey agar) is typically associated with Escherichia coli O157:H7 rather than Serratia marcescens, which does not utilize sorbitol and would not produce clear colonies on this medium. Thus, the defining characteristic of bright red pigment production effectively identifies Serratia marcescens in microbiological practice.