Molecular epidemiology of Staphylococcus epidermidis isolates in a hematological unit during a 4-month survey

In order to study the strain variety, clonal stability and epidemiology of Staphylococcus epidermidis, isolates from all bacterial cultures taken when clinically indicated in 2 wards of the hematological unit of Helsinki University Hospital, during a 4-month period, were characterized by 3 typing methods: antibiogram, plasmid profile and ribotype. A total of 141 distinct S. epidermidis colonies, from 28 blood cultures and 37 cultures from other sources in 32 patients were studied. Plasmid profiles and ribopatterns revealed 47 different strains of which 16 were bacteremic. One of these strains caused bacteremia in 4 different patients over a 3-month period and it was isolated from blood on 7 different sampling occasions. The occurrence of this clone was constant; it was usually found in both of 2 blood culture bottles inoculated (6/7 pairs) and dominated among the 17 distinct S. epidermidis colonies studied from the positive bottles (94% of the total). The clones causing bacteremias in the 2 wards were distinct. These findings indicate that certain clones of S. epidermidis can predominate in hematological wards and that nosocomial transmission of S. epidermidis strains may occur among patients, particularly within the same ward.