TYPING OF RED PIGMENTED SERRATIA-MARCESCENS ISOLATED FROM HOSPITALS

Among 994 strains of Serratia marcescens isolated from nosocomial infections in Belgium, thirty eight appeared to be red pigmented. They were characterized with respect to serotype, biotype, antibiotic susceptibility pattern and plasmid carriage. A wide variation of serotypes was demonstrated with O-5:H-2 as the most prevalent serotype. Following the biotype scheme of Grimont, biotypes A1a and A2a predominated; biotype A2a coud be further differentiated into two subtypes (146, 106) according to the biotype scheme of Traub. Most strains were either sensitive to 14 antibiotics or only streptomycin resistant; multiresistance was infrequently encountered. Contrary to Literature data, red pigmented S. marcescens has the potentiality to carry plasmids : 18% of the strains were found to carry one single plasmid with variable size (greater than or equal to 44 kb). The combination of serotyping, biotyping, antibiotic susceptibility and plasmid typing could discriminate between different clones isolated at a same hospital; however in some cases (antibiotic sensitive or plasmid free strains) other typing methods (i.e. molecular) should be performed.