The Burkholderia cepacia complex (BCC) is a collection of Gram-negative bacteria that function as opportunistic pathogens. These organisms are a serious concern within healthcare environments, especially for patients with underlying health issues. The BCC can cause severe, sometimes fatal, infections in vulnerable individuals. While its natural habitat is the environment, it has adapted to colonize and infect human hosts, making it a persistent clinical challenge.
Defining the Burkholderia cepacia Complex
The BCC is not a single bacterial species but a group of over 20 genetically distinct species, often referred to as genomovars. These organisms are classified as Gram-negative bacteria. The specific BCC species causing an infection influences the clinical outcome.
The primary group at high risk for BCC infection comprises individuals with underlying respiratory diseases, most notably cystic fibrosis (CF). CF patients are uniquely susceptible because impaired mucociliary clearance prevents effective bacterial removal from their airways. This creates a favorable, chronically inflamed environment for BCC to establish an infection.
Other vulnerable populations include immunocompromised patients, such as those with chronic granulomatous disease, and patients in intensive care units. The BCC also causes nosocomial infections, or those acquired in a hospital setting, in non-CF patients, often linked to contaminated medical products. The complex’s broad metabolic capabilities allow it to survive in various harsh conditions, contributing to its opportunistic nature.
Clinical Impact and Disease Progression
In patients with cystic fibrosis, BCC acquisition leads to two major clinical outcomes. Chronic colonization of the airways is the more common outcome, associated with a rapid decline in lung function. This chronic infection often leads to increased morbidity and requires ongoing management to suppress bacterial loads.
The second, more devastating outcome is “cepacia syndrome,” a rapidly progressive and severe illness. This syndrome is characterized by high fever, necrotizing pneumonia, and bacteremia, which is the presence of bacteria in the bloodstream. Deterioration can be swift, resulting in sepsis and respiratory failure with a high mortality rate, sometimes reaching 75%. Certain BCC species, such as Burkholderia cenocepacia (the epidemic ET-12 strain), are associated with a higher risk of developing this fatal syndrome.
Due to the transmissible nature and severe potential of some BCC strains, stringent patient isolation protocols are necessary. Segregation of BCC-positive CF patients from uninfected individuals is a standard infection control practice to prevent cross-infection. The presence of BCC can also complicate eligibility for lung transplantation, as post-transplant outcomes are often poor for colonized individuals.
Routes of Transmission and Environmental Persistence
The Burkholderia cepacia complex is highly adaptable, thriving in diverse environments outside the human body, including soil and water sources where it persists for prolonged periods. This environmental versatility extends to hospital settings, where BCC survives in moist environments like disinfectants, antiseptic solutions, and various water-based hospital equipment.
Transmission occurs primarily through direct contact, especially between CF patients in clinical or social settings, spreading via respiratory secretions, such as from coughing or close personal contact. Indirect transmission is also significant, occurring when a vulnerable patient encounters contaminated environmental sources.
Contaminated medical devices and pharmaceutical products are frequent culprits in outbreaks. Examples include nebulizers, saline solutions, and oral liquid medications, which the bacteria colonize and use as a vehicle for infection. Rigorous infection control measures are necessary in all healthcare facilities to limit the spread of these organisms.
Antibiotic Resistance and Treatment Strategies
One of the greatest challenges in managing BCC infections is the organism’s high intrinsic resistance to numerous common antibiotics. This inherent resistance stems from sophisticated mechanisms that allow the bacteria to survive antibiotic exposure. One mechanism is the low permeability of the BCC’s outer membrane, which acts as a barrier preventing the entry of many antimicrobial agents.
Another significant defense mechanism involves efflux pumps. These pumps actively push antibiotics out of the bacterial cell before they can reach their intended target, conferring multidrug resistance. BCC also produces enzymes, such as \(\beta\)-lactamases, that chemically inactivate antibiotics like ceftazidime.
Treatment for BCC infection is complex and typically guided by specific susceptibility testing. A common therapeutic approach involves using a combination of multiple antibiotics to overcome high resistance levels. Agents frequently considered include ceftazidime, meropenem, trimethoprim-sulfamethoxazole (TMP-SMX), and minocycline. Since complete eradication is often difficult, treatment focuses on long-term suppression to slow the decline in lung function.