Epidemic Achromobacter xylosoxidans strain among Belgian cystic fibrosis patients and review of literature

Abstract

Background: Achromobacter xylosoxidans is increasingly being recognized as an emerging pathogen in cystic fibrosis. Recent severe infections with A. xylosoxidans in some of our cystic fibrosis (CF) patients led to a re-evaluation of the epidemiology of CF-associated A. xylosoxidans infections in two Belgian reference centres (Antwerp and Ghent). Several of these patients also stayed at the Rehabilitation Centre De Haan (RHC). In total, 59 A. xylosoxidans isolates from 31 patients (including 26 CF patients), collected between 2001 and 2014, were studied. We evaluated Matrix Assisted Laser Desorption Ionisation -Time of Flight mass spectrometry (MALDI-TOF) as an alternative for McRAPD typing.

Results: Both typing approaches established the presence of a major cluster, comprising isolates, all from 21 CF patients, including from two patients sampled when staying at the RHC a decade ago. This major cluster was the same as the cluster established already a decade ago at the RHC. A minor cluster consisted of 13 isolates from miscellaneous origin. A further seven isolates, including one from a non-CF patient who had stayed recently at the RHC, were singletons.

Conclusions: Typing results of both methods were similar, indicating transmission of a single clone of A. xylosoxidans among several CF patients from at least two reference centres. Isolates of the same clone were already observed at the RHC, a decade ago. It is difficult to establish to what extent the RHC is the source of transmission, because the epidemic strain was already present when the first epidemiological study in the RHC was carried out. This study also documents the applicability of MALDI-TOF for typing of strains within the species A. xylosoxidans and the need to use the dynamic cutoff algorithm of the BioNumerics® software for correct clustering of the fingerprints.

Keywords: Achromobacter xylosoxidans; Cystic fibrosis; Epidemic strain; MALDI-TOF MS typing; McRAPD.

Fig. 1

McRAPD profiles, representative for each of the clusters, pairs and singletons. a Clusters (I and II); b: Pairs (P1 and P2); c: Singletons (S1, S2 and S3)

Fig. 2

Detailed comparison of two MALDI-TOF MS main spectra (MSPs). a Alignment of two MSPs, representative for cluster I (red, above) and cluster II (blue, below). Spectrum range 2000–10000 m/z. b–c Enlargement of part of the spectrum (6000–7500 m/z): Gel view representation (b) and peak view presentation (c). Only peaks with a central line are taken into account for comparison by the BioNumerics® software

Fig. 3

UPGMA constructed tree, based on MALDI-TOF main spectra (MSPs) of 59 isolates (with isolate CF GUH 86–1 tested in duplo). At the left: Clusters, Pairs (P) and Singletons (S). Tree lines indicated in bold refer to the clustering obtained by the BioNumerics® software on the basis of MSPs. Isolate designations: CF from cystic fibrosis patient, NCF from non-cystic fibrosis patient, AUH from patient from Antwerp University Hospital, GUH from patient from Ghent University Hospital, RHC from patient when staying at the Rehabilitation Centre at De Haan (period: 2001–2002), Coll from culture collection of Georges Wauters (Université Libre Bruxelles, Belgium), ^T type strain; −# numbering of different isolates from the same patient. Y*: Isolate from CF patient during his/her stay at the RHC, during the period 2001–2002. Affixes ‘S’ and ‘V’ indicate the clusters to which they had been assigned [14]. Y**: Recent isolate from a CF patient of which isolates were also collected during a previous stay (period 2001–2002) at the RHC [14], and for whom the isolates were shown to belong to cluster V. At the right: Connector lines indicate some examples whereby multiple isolates of the same patient are clustered differently according to whether the interpretation is done by human observers or by the BioNumerics® software, i.e. patients CF AUH 2, CF GUH 4 and CF GUH 108

Fig. 4

Multi-dimensional scaling (MDS), representing the MALDI-TOF main spectra (MSPs) of the isolates from Cluster I (red dots), Cluster II (green dots), and the isolates not belonging to one of these clusters (grey dots). a Side view. b Top view