1. Department of Microbiology, Institute of Tropical Medicine, 2000 Antwerp, Belgium and Medical Research Council Laboratories, Fajara, The Gambia, West Africa.
2. Department of Microbiology, Institute of Tropical Medicine, 2000 Antwerp, Belgium.
3. Department of Microbiology, Institute of Tropical Medicine, 2000 Antwerp, Belgium and Flanders Interuniversity Institute for Biotechnology, VIB, 9052 Zwijnaarde, Belgium.
4. Medical Research Council Laboratories, Fajara, The Gambia, West Africa.
5. Department of Microbiology, Institute of Tropical Medicine, 2000 Antwerp, Belgium