Burkholderia cepacia complex: Opportunistic pathogens in patients with cystic fibrosis - Culture; Molecular diagnosis (PCR); Species identification (PCR and sequencing).
The Burkholderia cepacia complex is a group of closely related bacterial species. For a long time it was believed that B. cepacia was only a plant pathogen. Subsequently, its role as an important opportunistic pathogen that causes morbidity and mortality in immunocompromised persons was discovered, especially in those with cystic fibrosis and chronic granulomatous disease. In addition, numerous outbreaks of nosocomial infections due to person-to-person transmission or equipment contamination have been documented. The B. cepacia complex can cause bacteremia, septic arthritis, osteomyelitis, meningitis, peritonitis, urinary tract and respiratory infections, and endocarditis. Despite being recognized as opportunistic pathogens, some species of the B. cepacia complex are significantly important as human pathogens because they have a high degree of resistance to antibiotics, an exceptional transmissibility in nosocomial environments and a high capacity to survive intracellularly.
The Burkholderia cepacia complex includes up to 22 species. These species form a very stable group within the genus Burkholderia when the 16S rDNA gene is phylogenetically analyzed and they present up to 78% of their genes in common. Despite their similarities, a significant number of species of the B. cepacia complex are being characterized to formally name them as new species. In general, these species have large genomes (up to 9 Mpb) divided into 2-5 replicons, typically arranged in three chromosomes and a large plasmid. This characteristic provides a great metabolic versatility that is considered important to inhabit soil, water, plants, and nodules of legumes. B. cepacia can even survive for a long period of time and multiply easily in aqueous environments, such as disinfectants and intravenous fluids used in hospitals.
Burkholderia cepacia was originally intended for agricultural purposes since some species of the complex exhibit beneficial activities such as bioremediation, biocontrol and promotion of plant growth. In 1950 it began to use B. cepacia as a biopesticide due to its ability to antagonize a series of pathogens of plants transmitted by soil mediated, to some extent, by antifungal substances secreted by the body. However, due to its role in human infections, its use in agriculture is currently restricted.
In the early 1980s, the Burkholderia cepacia complex was described as opportunistic human pathogens capable of causing particularly serious and life-threatening infections for patients with cystic fibrosis. Cystic fibrosis is a genetic disease that causes an abnormality in the secretions of the exocrine glands, which mainly affects the lungs and the digestive system. In patients with this disease, the lower airways become clogged with dehydrated, viscous mucus. These conditions constitute an ideal environment in which species of the B.cepacia complex can establish chronic infections that impede the normal functioning of the lung, causing pneumonia, which can in turn lead to septicemia and, in some cases, to the death of the patient. This progressive and rapid deterioration of the patients was called the "cepacia syndrome", characterized by a necrotizing pneumonia, quickly and frequently lethal, accompanied by septicemia, which develops in up to 20% of infected patients.
Patients can acquire species of the B. cepacia complex either from the environment or through patient-to-patient transmission, through hospital material or fomites between people after a contact of several weeks or months. B. cepacia usually produces nosocomial infection due to contamination of disinfectants, medical equipment, prosthetic material and drugs, such as anesthetics or urological irrigation fluids. In the 1990s, the first dissemination of patients to patients of the B.cepacia complex was reported. The recognition of transmissible strains within this complex led to the improvement of microbiological detection protocols and the implementation of strict infection control policies that resulted in lower rates of person-to-person transmission, and in the reduction of cross-strain infections. epidemic However, sporadic cases of infections with the B. cepacia complex continue to occur.
B. cenocepacia and B. multivorans represent the great majority (85%) of the isolates of patients with cystic fibrosis, although all the species of the complex have the potential to infect these patients. Epidemiological studies conducted in the 1980s and 1990s showed that outbreaks in cystic fibrosis centers were mainly caused by particularly virulent and transmissible strains of B. cenocepacia, such as the ET12, PHDC and Midwest lineages. Infection control measures adopted around the world led to a reduction in the prevalence of B. cenocepacia. Probably, as a result of these measures, the appearance of non-clonal strains of species of the B.cepacia complex, such as B. multivorans, B. contaminans, B. pyrrocinia, B. vietnamiensis, B.stabilis and B. dolosa, is now evident. .
In addition to cystic fibrosis, people with chronic granulomatous disease or other immunodeficiencies are also predisposed to infection by the B. cepacia complex species. At present, it is considered that B. cepacia infection could be a clinical marker of deterioration of the defense system in immunosuppressed or critically ill patients, proposing that infection by this low virulence bacterium should compel the clinician to rule out immunodeficiencies, including chronic granulomatous disease. Also, the B. cepacia complex can cause opportunistic infections in hemodialysis patients with endovascular catheter, endocarditis in neonates, pneumonias in patients treated with broad-spectrum antibiotics and patients with mechanical ventilation, infections in burns or surgical wounds, post-surgical eye infections, and urinary tract infections in patients with probes.
Infections with the B.cepacia complex are difficult to treat due to the intrinsic resistance of these bacteria to the current antimicrobial agents. The intrinsic resistance to antibiotics is caused by the physicochemical properties of a bacterium, such as the exclusion of drug molecules by the outer membrane. Most species of Burkholderia contain a modified lipopolysaccharide that causes intrinsic resistance to polymyxins, by preventing their binding to the outer membrane. Also, they have restrictive porins that contribute to the reduction of the penetration of drugs. In addition to the intrinsic resistance, the efflux pumps present in B.cepacia constitute the main multiresistance factors. Finally, depending on the species, the bacteria can have different acquired resistance, to β-lactam antibiotics due to the existence of β-lactamases, or to other antibiotics thanks to the mutation of their targets.
The detection of species of the Burkholderia cepacia complex can be done by culture or molecular methods (PCR). The identification of B. cepacia complex species is always a tedious task for the routine microbiology laboratory. In these laboratories, the identification of the isolates of the B. cepacia complex is generally done using a combination of selective media, conventional biochemical analyzes and commercial systems. The molecular techniques developed in recent years are a very useful tool for detection, identification, confirmation, and discrimination beyond the level of the species.
Tests carried out in IVAMI:
- Detection of B.cepacia by isolation in culture.
- Detection of B.cepacia by molecular methods (PCR).
- Identification of the B.cepacia complex species (PCR and sequencing).
- In patients with cystic fibrosis, respiratory samples are accepted and, in case of suspicion of septicemia, whole blood extracted with EDTA (5 mL).
- Depending on the location of the infection, different samples will be accepted: respiratory samples, blood, urine, CSF, peritoneal fluid, and biopsies from different tissues.
Conservation and shipment of the sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen for more than 2 days.
Delivery of results:
- Detection of B.cepacia by isolation in culture: 5 to 7 days.
- Detection of B.cepacia by molecular methods (PCR): 24 to 48 hours.
- Identification of the B.cepacia complex species (PCR and sequencing): 48 to 72 hours.
Cost of the test:
- Detection of B.cepacia by isolation in culture: Consult firstname.lastname@example.org.
- Detection of B.cepacia by molecular methods: Consult email@example.com.
- Identification of the B.cepacia complex species: Consult firstname.lastname@example.org.