Clinical relevance and virulence factors of pigmented Serratia marcescens

Pigmented Serratia marcescens isolated in a Brazilian hospital were studied with respect to frequency of isolation, serotyping, antibiotic resistance and virulence factors. The serotype most frequent was O6:K14(53%) and all isolates were resistant to ampicillin, cephalothin and tetracycline. The majority of the isolates (92%) were resistant to the action of human serum and all produced cytotoxins on Vero, CHO, HEp-2 and Mt La cells. These isolates were virulent for mice (LD50 = 10(7) bacteria ml(-1)) and showed virulence factors, but were isolated with low frequency (3.4%) and caused infection in only 31% of cases. Analysis of serotyping, phage typing and chromosomal DNA revealed at least 13 unrelated strains among pigmented S. marcescens. In conclusion, this work describes a low frequency of isolation of pigmented S. marcescens from clinical specimens, indicating that non-pigmented strains are clinically more significant. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.