Variation ofBurkholderia cenocepaciavirulence potential during cystic fibrosis chronic lung infection

Abstract

During long-term lung infection in cystic fibrosis (CF) patients, Burkholderia cenocepacia faces multiple selective pressures in this highly stressful and fluctuating environment. As a consequence, the initial infecting strain undergoes genetic changes that result in the diversification of genotypes and phenotypes. Whether this clonal expansion influences the pathogenic potential is unclear. The virulence potential of 39 sequential B. cenocepacia (recA lineage IIIA) isolates, corresponding to 3 different clones retrieved from 3 chronically infected CF patients was compared in this study using the non-mammalian infection hosts Galleria mellonella and Caenorhabditis elegans. The isolates used in this retrospective study were picked randomly from selective agar plates as part of a CF Center routine, from the onset of infection until patients' death after 3.5 and 7.5 y or the more recent isolation date after 12.5 y of chronic infection. The infection models proved useful to assess virulence potential diversification, but for some isolates the relative values diverged in C. elegans and G. mellonella. Results also reinforce the concept of the occurrence of clonal diversification and co-existence of multiple phenotypes within the CF lungs, also with respect to pathogenicity. No clear trend of decrease (or increase) of the virulence potential throughout long-term infection was found but there is an apparent tendency for a clone/patient-dependent decrease of virulence when the G. mellonella model was used. The sole avirulent variant in both infection hosts was found to lack the small third replicon previously associated to virulence. Although possible, the in vivo loss of this nonessential megaplasmid was found to be a rare event (1 among a total of 64 isolates examined).

1H-NMR-Based Endometabolome Profiles of Burkholderia cenocepacia Clonal Variants Retrieved from a Cystic Fibrosis Patient during Chronic Infection

“…Consistent with this conclusion is the expression proteomic data previously obtained for isolates IST4113 and IST4134 that also indicates that the number of proteins exhibiting different content in IST439 compared with the two late isolates is lower for IST4134 than for IST4113, with several proteins showing an altered content in IST4113, but not in IST4134, compared to IST439 (Madeira et al, 2013). The endometabolome profile analysis also showed that the clonal variant IST4129 lacking the third replicon (Moreira et al, 2016), exhibits the most distinct metabolic profile. Even though IST4129 and IST4134 were retrieved in the last stages of the illness at isolation dates separated by only 9 months (Coutinho et al, 2011a), it is intriguing why the loss of such a large genomic element in IST4129 does not significantly change the relative abundances of several of the metabolites that were identified in these isolates.…”

“…However, since this isolate lacks the third replicon, a genomic element previously shown to be essential for stress resistance (Agnoli et al, 2014), its higher susceptibility to stress is not unlikely. The in vivo loss of this third replicon is a rare event (Agnoli et al, 2014; Moreira et al, 2016), and the loss of this megaplasmid involved in stress resistance, virulence and secondary metabolism is not expected to confer any advantage in the highly stressful CF environment. Thus, it is tempting to speculate that the higher abundance of glycine-betaine in isolate IST4129 could be a competitive factor contributing to the persistence of this clonal variant in the CF airways and, consequently, to its isolation.…”

“…The four Burkholderia cenocepacia clonal variants examined in this study, IST439, IST4113, IST4129 and IST4134, were recovered from the sputum of a CF patient under surveillance at the major Portuguese CF Center in the Hospital de Santa Maria from Centro Hospitalar Lisboa Norte EPE, Lisbon, from January 1999 to July 2002, as part of the hospital routine (Cunha et al, 2003; Coutinho et al, 2011a; Moreira et al, 2016). For each isolation date, one well isolated colony capable of growing onto the selective B. cepacia Selectatab medium was picked at random.…”

“…This metabolomics analysis was based on 1 H-NMR aiming to unveil the alterations occurring in the metabolome of these B. cenocepacia clonal variants during a chronic infection. This comparative analysis was extended to a fourth clonal variant (IST4129) retrieved from the same CF patient 3 months before death with the cepacia syndrome when the clinical condition worsened, given that it was found to lack the third replicon (Moreira et al, 2016). This replicon is required for virulence, tolerance to multiple stresses, D -xylose, pyrimidine and fatty acid utilization, as well as exopolysaccharide production and protease activity in some strains (Agnoli et al, 2012, 2014).…”

“…Moreover, from the 776 predicted coding sequences of the B. cenocepacia J2315 third replicon, a high percentage corresponds to hypothetical proteins and genes with unknown function (Holden et al, 2009). Since our goal was to compare the data gathered in the present work for four previously characterized clonal variants (Cunha et al, 2003; Coutinho et al, 2011a; Moreira et al, 2016) retrieved from the same patient during chronic infection with the information previously obtained using other genome-wide expression approaches, cells were grown under conditions identical to those tested before and though to mimic those expected to occur during growth in the CF lung (Madeira et al, 2011, 2013; Mira et al, 2011). Although static measurement of metabolite pool sizes cannot be used to infer about metabolic fluxes, the observed changes may indicate potential alterations in pathway activity (Nandakumar et al, 2014).…”