Intragenomic and intraspecific heterogeneity of the 16S rRNA gene in seven bacterial species from the respiratory tract of cystic fibrosis patients assessed by PCR-Temporal Temperature Gel Electrophoresis

Effect of Intragenomic Sequence Heterogeneity among Multiple 16S rRNA Genes on Species Identification of Elizabethkingia

Accurate identification of Elizabethkingia species mostly requires the use of molecular techniques, and 16S rRNA gene sequencing is generally considered the method of choice. In this study, we evaluated the effect of intraspecific diversity among the multiple copies of the 16S rRNA gene on the accuracy of species identification in the genus Elizabethkingia. Sequences of 16S rRNA genes obtained from the 32 complete whole-genome sequences of Elizabethkingia deposited in GenBank and from 218 clinical isolates collected from 5 hospitals in Taiwan were analyzed. Four or five copies of 16S rRNA were identified in the Elizabethkingia species with complete genome sequences. The dissimilarity among the copies of the16S rRNA gene was <1% in all Elizabethkingia strains. E. meningoseptica demonstrated a significantly higher rate of nucleotide variations in the 16S rRNA than did E. anophelis (P = 0.011). Nucleotide alterations occurred more frequently in regions V2 and V6 than in other hypervariable regions (P < 0.001). E. meningoseptica, E. anophelis, and E. argenteiflava strains were clustered distinctly in the phylogenetic tree inferred from 16S rRNA genes, and the intragenomic variation of gene sequences had no profound effect on the classification of taxa. However, E. miricola, E. bruuniana, E. ursingii, and E. occulta were grouped closely in the phylogenetic analysis, and the variation among the multiple copies of the 16S rRNA in one E. ursingii strain affected species classification. Other marker genes may be required to supplement the species classification of closely related taxa in the genus Elizabethkingia. IMPORTANCE Incorrect identification of bacterial species would influence the epidemiology and clinical analysis of patients infected with Elizabethkingia. The results of the present study suggest that 16S rRNA gene sequencing should not be considered the gold standard for the accurate identification of Elizabethkingia species.

16S rRNA gene sequencing on a benchtop sequencer: accuracy for identification of clinically important bacteria

AIMS

Test the choice of 16S rRNA gene amplicon and data analysis method on the accuracy of identification of clinically important bacteria utilizing a benchtop sequencer.

METHODS AND RESULTS

Nine 16S rRNA amplicons were tested on an Ion Torrent PGM to identify 41 strains of clinical importance. The V1-V2 region identified 40 of 41 isolates to the species level. Three data analysis methods were tested, finding that the Ribosomal Database Project's SequenceMatch outperformed BLAST and the Ion Reporter Metagenomics analysis pipeline. Lastly, 16S rRNA gene sequencing mixtures of four species through a six log range of dilution showed species were identifiable even when present as 0·1% of the mixture.

CONCLUSIONS

Sequencing the V1-V2 16S rRNA gene region, made possible by the increased read length Ion Torrent PGM sequencer's 400 base pair chemistry, may be a better choice over other commonly used regions for identifying clinically important bacteria. In addition, the SequenceMatch algorithm, freely available from the Ribosomal Database Project, is a good choice for matching filtered reads to organisms. Lastly, 16S rRNA gene sequencing's sensitivity to the presence of a bacterial species at 0·1% of a mixture suggests it has sufficient sensitivity for samples in which important bacteria may be rare.

SIGNIFICANCE AND IMPACT OF THE STUDY

We have validated 16S rRNA gene sequencing on a benchtop sequencer including simple mixtures of organisms; however, our results highlight deficits for clinical application in place of current identification methods.

Highly Diversified Pandoraea pulmonicola Population during Chronic Colonization in Cystic Fibrosis

Several environmental bacteria are considered as opportunistic pathogens in cystic fibrosis (CF) and are able to persistently colonize the CF respiratory tract (CFRT). Beside Pseudomonas aeruginosa and Burkholderia cepacia complex, Pandoraea spp. are defined as pathogenic. During chronic colonization, adaptive evolution and diversified population have been demonstrated, notably for P. aeruginosa. However, the persistence of Pandoraea in the CFRT remains largely unexplored. We studied genomic and phenotypic traits of Pandoraea pulmonicola isolates successively recovered from the airways of a single CF patient and relate the results to qualitative and quantitative evolution of other cultivable pathogens and to patient clinical status. A total of 31 isolates recovered from 18 sputum samples over a 7-year period in a single CF patient were studied. Genome dynamics was assessed by pulsed-field gel electrophoresis, ERIC-PCR fingerprinting and 16S rRNA gene PCR-temporal temperature gel electrophoresis. Phenotypic features included antimicrobial susceptibility, motility, biofilm production, and virulence in Caenorhabditis elegans model. Variability was observed for all the characteristics studied leading to highly diversified patterns (24 patterns) for the 31 clonally related isolates. Some of these modifications, mainly genomic events were concomitantly observed with CFRT microbiota composition shifts and with severe exacerbations. The diversity of P. pulmonicola population studied, observed for isolates recovered from successive samples but also within a sample suggested that existence of a diversified population may represent a patho-adaptive strategy for host persistence in the heterogeneous and fluctuating CFRT environment.

Bacterial infections in patients with primary ciliary dyskinesia: Comparison with cystic fibrosis

Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder associated with severely impaired mucociliary clearance caused by defects in ciliary structure and function. Although recurrent bacterial infection of the respiratory tract is one of the major clinical features of this disease, PCD airway microbiology is understudied. Despite the differences in pathophysiology, assumptions about respiratory tract infections in patients with PCD are often extrapolated from cystic fibrosis (CF) airway microbiology. This review aims to summarize the current understanding of bacterial infections in patients with PCD, including infections with Pseudomonas aeruginosa, Staphylococcus aureus, and Moraxella catarrhalis, as it relates to bacterial infections in patients with CF. Further, we will discuss current and potential future treatment strategies aimed at improving the care of patients with PCD suffering from recurring bacterial infections.

Intrapatient diversity of Achromobacter spp. involved in chronic colonization of Cystic Fibrosis airways

Achromobacter spp. are increasingly identified in Cystic Fibrosis (CF) patients and their ability to persistently colonize the CF respiratory tract (CFRT) suggests that Achromobacter species possess adaptive characteristics. We studied genome dynamics in 118 isolates recovered from 13 patients with Achromobacter chronic colonization (5-26 isolates per patient recovered over 13-61 months). Isolates were identified to species level by nrdA gene sequencing, subjected to Pulsed-Field Gel Electrophoresis (PFGE) and multiplex rep-PCR (MR-PCR), and rrs intragenomic diversity was studied by PCR-Temporal Temperature Gel Electrophoresis (TTGE). Intrapatient diversity was assessed: (i) from dynamics of XbaI and/or SpeI-based pulsotypes, (ii) from comparison of MR-PCR profiles, and (iii) by longitudinal analysis of rrs intragenomic diversity. Patients were chronically colonized by Achromobacter xylosoxidans (n=10), Achromobacter dolens (n=1) or Achromobacter insuavis (n=2). All strains displayed genomic diversification over time but A. insuavis showed higher pulsotype diversity compared to other species. Intragenomic rrs heterogeneity was found in strains from 6 of 13 patients and may be persistently observed. Achromobacter genome evolution observed during chronic colonization of the CFRT warrants further investigation of the adaptation features of the different species, as well as of the selective forces driving this adaptation in the CFRT.