[1] UNIV LIEGE,INST CHIM,SERV MICROBIOL,B-4000 LIEGE,BELGIUM
[2] STATE UNIV GHENT,MICROBIOL & MICROBIELE GENET LAB,B-9000 GHENT,BELGIUM
[3] UNIV OXFORD,SIR WILLIAM DUNN SCH PATHOL,OXFORD OX1 3RE,ENGLAND
[4] UNIV OXFORD,DEPT BIOCHEM,OXFORD OX1 3QU,ENGLAND