** Serratia spp (FIG.3)
are gram-negative bacteria, classified in the large family of Enterobacteriaceae. Serratia spp can be distinguished from other genera by its production of three special enzymes DNAase, lipase and gelatinase. However, a number of other traits have been identified that may contribute to pathogenesis. These include swimming and swarming motility and extracellular enzyme activities, i.e. nuclease, protease and haemolysin. Serratia spp occur in water and soil, on plant, in insects and in man and animal. S. marcescens is the only pathogenic species, although rare reports of infection with S. plymuthica, liquefaciens, rubidaea and odifera exist. Since the early 1900ís, physicians have used S. marcescens to study transmission of microorganisms, as it was assumed to be a harmless saprophyte. In the hospital, Serratia tends to colonize the respiratory and urinary tracts of adults, rather than the GI tract. Serratia sp is responsible for 1.4% of nosocomial septicemia. It is also responsible for 2% of lower respiratory, urinary tract and surgical wound infections. Serratia sp can be a cause of meningitis, especially after surgical intervention. Also reported is endocarditis and osteomyelitis in heroin addicts. Crude mortality for Serratia septicemia is 26%, while the mortality for meningitis and endocarditis is very high. S. marcescens and S. liquefaciens may cause lethal septicaemia in insects.4