In this review we aim to give a contribution to the understanding of relevant aspects of Bcc bacteria-mediated respiratory infections in CF patients, based on the epidemiological surveys carried out by our research group of a case-study population that has been routinely followed for the past 16 years at the CF Treatment Center of Santa Maria Hospital (HSM), in Lisbon. This CF population comprises a total of 124 patients, of which 58% are children (up to 18 years old) and 42% are adults (Figure 1). In the CF pediatric population 54% are female and 46% are male, while in the CF adult population 58% are females and 42% males. Bcc bacteria have been isolated from 41 of these patients, belonging to both the adult (n = 12) and pediatric (n = 29) populations. The age at the time of the first Bcc isolation varied between a few months of life and 28 years old, with an estimated mean age of 10 years.
Studies involving the use of B. cenocepacia isolates collected from CF patients at HSM were approved by the ethics committee of the Hospital, and the anonymity of the patients is preserved.
The CF subpopulation is represented by a collection of 506 Bcc clinical isolates and clonal variants that were gathered during our 16-year collaboration with the HSM CF Center. This collection includes serial isolates recovered from persistently colonized patients from the early to late stages of infection. According to this routine, sputum samples are obtained from CF patients every 2-3 months, during periodic consultations to monitor their clinical status, or more often for patients showing clinical deterioration (Cunha et al.,). The systematic molecular analysis of the 506 isolates revealed that the most prevalent Bcc species recovered from the sputa of the 41 Bcc-infected patients are B. cepacia and B. cenocepacia (Figure 2A).
While B. cepacia is not a predominant Bcc species among the CF population characterized worldwide (Mahenthiralingam and Vandamme,), detailed molecular analysis unveiled an exceptionally high incidence of B. cepacia at the HSM CF Center from 2003 to 2005 (Figure 2B), with isolates being retrieved from 11 out of 13 Bcc-infected patients (Cunha et al.,). This abnormal prevalence of B. cepacia was associated with two B. cepacia clones that were indistinguishable from two strains isolated from contaminated non-sterile saline solutions for nasal application, detected during routine market surveillance by the Portuguese Medicines and Health Products Authority, INFARMED (Cunha et al.,). After this contamination was detected, the number of B. cepacia isolates identified at HSM gradually declined over the following years, although still remaining significantly high due to persistent colonization of the living patients (Figure 2B). Interestingly, 2005 coincides with a peak in the number of CF patients with newly detected Bcc infections (Figure 2C). Although transmission of Bcc bacteria is considered an important factor in the colonization of CF patients, other primary sources of infection must be taken into account in CF centers where the recommended control measures are followed, as is the case of the CF center at HSM. It is likely that the environment might act as a reservoir for novel Bcc infections (Pallud et al.,; LiPuma et al.,; Vanlaere et al.,), and attention should be given to continuous monitoring of medication for microbial contaminations. Indeed, Bcc bacteria are resistant to multiple antimicrobials and to diverse growth inhibitors that can even be used as carbon sources (Coenye and Vandamme,). Since these bacteria also have minimal nutritional requirements, they are able to grow in aqueous products, including disinfectants (Oie and Kamiya,; Ghazal et al.,). Contamination of albuterol and sulbutamol nebulization solutions (Balkhy et al.,; Ghazal et al.,), nebulizers (Hutchinson et al.,), mouthwash (Matrician et al.,), nasal sprays (Dolan et al.,), and ultrasound gel (Jacobson et al.,) have resulted in outbreaks of nosocomial infections by Bcc bacteria. Therefore, the surveillance of unexplained outbreaks of less common pathogens is essential; in particular, those involving poorly represented species, like B. cepacia, especially in patients with underlying lung disease and increased risk such as CF patients.
In addition to B. cenocepacia and B. cepacia, four other Bcc species have been isolated from the HSM CF population: B. dolosa, B. contaminans, B. stabilis, and B. multivorans (Cunha et al.,, unpublished results; Figures 2A,B,D). Because the taxonomy of Bcc bacteria evolved significantly in the last few years, with the description of eight novel species (Vanlaere et al.,), we have re-examined the species identification of several isolates from our collection. We paid special attention to isolates that were classified as B. cepacia with recA-RFLP profile K (Cunha et al.,), since this taxon was recently shown to comprise at least two novel species (Vanlaere et al.,), and the multilocus sequence typing (MLST) analysis revealed that several of those isolates now belong to the B. contaminans species. Co-infection with two or three different Bcc species was also observed in nine patients, mainly involving B. cenocepacia and B. cepacia, and in a smaller percentage with B. cenocepacia and B. contaminans, with B. cenocepacia, B. stabilis, and B. multivorans, or with B. cenocepacia and B. dolosa (Figure 2D). Although there is a generalized idea that B. cenocepacia is associated with greater morbidity and mortality in CF patients (Speert,; Mahenthiralingam et al.,), epidemiological surveys show that all of the species above are associated with poor clinical outcome, including the cepacia syndrome, and give rise to chronic and transient infections (Cunha et al.,; Drevinek and Mahenthiralingam,). In fact, it is not clear why strains of different Bcc species differ in their persistence, epidemiology, and pathogenic potential in CF, or why the same strain can be associated with very different clinical outcomes. It probably depends on factors that are inherent to each individual patient, on co-colonization by other pathogens and on other still unidentified factors.