2.2.3. Serratia marcescens

Members of the genus Serratia cause important infections in humans, animals, and insects. Taxonomically, the genus Serratia is confusing, and currently there are 14 recognized species, with 2 subspecies. The type species, Serratia marcescens, is an opportunistic human pathogen commonly found in the respiratory and urinary tracts of humans, and is responsible for approximately 1.4% of nosocomial infections that can be life-threatening.

While environmental S. marcescens strains are often red due to the production of prodigiosin, the strains associated with hospital outbreaks are mostly non-pigmented. As many S. marcescens strains are also resistant to multiple antibiotics, it represents a growing problem for public health. However, relatively little is known about the factors that contribute to S. marcescens pathogenesis within its host.

Yet, despite its animal virulence factors, Serratia has also been found to be a common phytopathogen. S. marcescens is recognized as a phloem-resident pathogen that causes cucurbit yellow vine disease of pumpkin (Cucurbita moschata L.), watermelon, and yellow squash (Cucurbita pepo L.), which is marked by wilting, phloem discoloration, and yellowing of foliage. S. marcescens produces a biofilm along the sides of the phloem vessels, blocking the transport of nutrients and eventually causing the plant to wilt and die.