Serratia

Serratia is a genus of Gram-negative, facultatively anaerobic, rod-shaped bacteria in the family Enterobacteriaceae. Members are typically non-spore-forming and motile by peritrichous flagella. They are oxidase negative and catalase positive, with varying abilities to ferment carbohydrates. A characteristic feature of several Serratia strains is the production of a red pigment, prodigiosin, especially at room temperature; pigment production often diminishes at higher temperatures.

Habitat and ecology: Serratia species are widespread in the environment, detected in soil, water, and plants, and they can reside as part of the transient human gut flora. They are also frequently encountered in clinical and hospital settings, where they may contaminate water systems, medical devices, and solutions.

Clinical relevance: Many Serratia species are opportunistic pathogens in humans. They can cause urinary tract infections, wound infections, pneumonia, bacteremia, and intra-abdominal infections, particularly in hospitalized or immunocompromised individuals. Outbreaks have been linked to contaminated medical equipment or solutions. Serratia marcescens is the best known clinically, but other environmental species can also cause infection, especially in vulnerable hosts.

Laboratory identification and treatment considerations: In culture, Serratia species may appear as non-lactose fermenters or slow lactose fermenters on standard media. They are oxidase negative and often form biofilms, contributing to persistence in clinical settings. Serratia species commonly possess intrinsic resistance mechanisms, including AmpC beta-lactamase activity, which influences antibiotic choices. Susceptibility testing guides therapy, with options depending on the strain and context.