A survey of potential virulence factors in clinical and environmental isolates of Serratia marcescens.

One hundred and forty seven isolates of Serratia marcescens were collected from diverse clinical and environmental sources in south-east Texas. Natural isolates were compared with hospital strains for the occurrence of 12 potential virulence determinants. Their overall frequency was as follows: haemolytic activity 48%; lecithinase 95%; lipase 95%; motility 99%; pigmentation 24%; plasmid carriage 46%; proteolytic activity 98%; siderophore activity 99%; urease activity 5%; mannose-sensitive haemagglutination 96%; mannose-resistant haemagglutination 61%; and mannose-resistant type-K haemagglutination (MR/K-HA) 68%. Clinical strains demonstrated a significantly higher occurrence of MR/K-HA (p less than 0.001) and non-pigmentation (p less than 0.01) than environmental isolates.