Detection of Pseudomonas mesophilica as a source of nosocomial infections in a bone marrow transplant unit

Abstract Pseudomonas mesophilica was isolated from fungal blood cultures of two bone marrow transplant recipients who consecutively occupied the same room. The isolation of P. mesophilica was temporally associated with febrile illness in these two granulocytopenic patients at 1 and 3 weeks posttransplant. A third patient, housed separately on the same bone marrow transplant unit, had nasopharyngeal colonization by this organism. Epidemiologic risk factors in common included staff, medications, and oral and perineal irrigations with tap water. Surveillance cultures detected P. mesophilica in none of 24 pharmaceutical preparations and in 10 of 40 tap water samples (100 to 600 CFU/ml) from implicated and control rooms on the same floor. Antimicrobial susceptibility testing of 14 patients and environmental isolates by agar dilution revealed similar profiles; some environmental isolates exhibited higher MICs. Because of restrictive nutritional and temperature requirements, P. mesophilica is undetected by many clinical laboratory protocols and may represent a previously undetected source of febrile illness in neutropenic patients.