Origins of Staphylococcus epidermidis and Streptococcus oralis causing bacteraemia in a bone marrow transplant patient

Departments of Microbiology and *Haematology, Royal Hospital for Sick Children, Yorkhill NHS Trust, Glasgow, Scottish MRSA Reference Laboratory and University Department of Bacteriology, Glasgow Royal Infirmary, Glasgow, Epidemiological Typing Unit, Laboratory of Hospital Infection, Central Public Health Laboratory, London and Department of Oral Microbiology, Glasgow Dental Hospital and School, Glasgow Corresponding author: Dr H. F. Kennedy. Received 4 Aug. 1999; accepted 9 Sept. 1999. Abstract Coagulase-negative staphylococcal bacteraemia in immunocompromised patients is often associated with the use of central venous catheters, while the proposed origin of viridans streptococci causing bacteraemia in this patient group is the oral cavity. This report describes an episode of polymicrobial bacteraemia caused by Staphylococcus epidermidis and Streptococcus oralis followed by several further episodes of S. epidermidis bacteraemia in a 15-year-old boy after bone marrow transplantation. Pulsed-field gel electrophoresis (PFGE) of Sma I chromosomal DNA digests was used to compare blood culture and oral isolates of S. epidermidis and Str. oralis . The results indicated that the mouth was the source of both S. epidermidis and Str. oralis causing the first episode of bacteraemia. PFGE further demonstrated that the central venous catheter was the origin of a second strain of S. epidermidis responsible for subsequent episodes of staphylococcal bacteraemia. Both the oral mucosa and central venous lines should be considered as potential sources of organisms, including coagulase-negative staphylococci, associated with bacteraemia in immunocompromised patients.