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.

Photodynamic Antimicrobial Chemotherapy (PACT) in combination with antibiotics for treatment of Burkholderia cepacia complex infection

This study aimed to determine if Photodynamic Antimicrobial Chemotherapy (PACT) was effective in the treatment of Burkholderia cepacia complex infection and whether a synergistic effect was evident if PACT was used in combination with antibiotics. The susceptibility of both planktonic and biofilm cultures of B. cepacia complex strains to methylene blue (MB) and meso-tetra(n-methyl-4-pyridyl)porphine tetra-tosylate (TMP)-mediated PACT was determined alone and in combination with antibiotics used in the treatment of Cystic Fibrosis pulmonary infection caused by these bacteria. When B. cepacia complex strains were grown planktonically, high levels of kill of were achieved with both TMP and MB-mediated PACT with strain and photosensitizer specific differences apparent. When strains were grown in biofilm, antibiotic treatment alone was bactericidal in 17/36 (47%) strain/antibiotic combinations tested. When antibiotic treatment was combined with PACT, bactericidal activity was apparent for 33/36 (92%) strain/antibiotic combinations. No antagonism was detected between PACT and antibiotic treatment with the combination synergistic for 6/36 (17%) and indifferent for 30/36 (83%) strain/antibiotic combinations. PACT could be a viable treatment option, either alone or in combination with antibiotics for treatment of B. cepacia complex pulmonary infection.