Intracellular survival and saprophytic growth of isolates from the Burkholderia cepacia complex in free-living amoebae

Members of the taxonomically diverse Burkholderia cepacia complex have become a major health risk for patients with cystic fibrosis (CF). Although patient-to-patient transmission of B. cepacia strains has been well-documented, very little is known about possible vehicles of transmission and reservoirs for these micro-organisms. In this work, it is shown that strains of the B. cepacia complex can survive within different isolates of the genus Acanthamoeba. Trophozoites containing bacteria developed profuse cytoplasmic vacuolization. Vacuolization was not detected in trophozoites infected with live Escherichia coli or heat-killed B. cepacia, or by incubation of trophozoites with filter-sterilized culture supernatants, indicating that metabolically active intracellular bacteria are required for the formation of vacuoles. Experiments with two different B. cepacia strains and two different Acanthamoeba isolates revealed that bacteria display a low level of intracellular replication approximately 72-96 h following infection. In contrast, extracellular bacteria multiplied efficiently on by-products released by amoebae. The findings suggest that amoebae may be a reservoir for B. cepacia and possibly a vehicle for transmission of this opportunistic pathogen among CF patients.