Summary auto-generated
This 1999 study investigated whether Burkholderia cepacia, a bacterium causing serious infections in cystic fibrosis patients, can survive inside free-living amoebae of the genus Acanthamoeba. Researchers cocultivated B. cepacia strains from clinical and environmental sources with multiple Acanthamoeba isolates. They found that metabolically active B. cepacia bacteria survive within cytoplasmic vacuoles in amoebae, producing characteristic vacuolization visible within 48 hours. Importantly, quantitative experiments revealed minimal intracellular bacterial replication (15-20 fold increase over 96-120 hours), while extracellular bacteria multiplied efficiently using nutrient by-products released by amoebae. Vacuolization required living bacteria—heat-killed bacteria and culture supernatants alone did not trigger this response. The infection pattern was species-dependent and temperature-dependent, with optimal infection occurring at 30°C. The findings suggest that amoebae may serve as environmental reservoirs for B. cepacia and potentially facilitate transmission between cystic fibrosis patients through inhalation of bacterial-containing amoeba vesicles or amoeba disintegration products.
Key findings
- B. cepacia strains from multiple genomovars survive within Acanthamoeba vacuoles, with metabolically active bacteria remaining motile for extended periods
- Intracellular bacterial replication is minimal (low-level growth), while extracellular saprophytic growth on amoeba-released by-products is the primary growth mechanism
- Amoebae may serve as environmental reservoirs and transmission vehicles for B. cepacia, potentially facilitating patient-to-patient spread in cystic fibrosis populations
- Infection is host-dependent (varies between amoeba strains) and temperature-dependent, with optimal infection at 30°C matching nasal temperature in humans
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Abstract
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.