www.wfcc.info/NEWSLETTER/newsletter34/a4.htmlB. cepacia was first described as Pseudomonas cepacia by Walter
Burkholder in 1950 for the phytopathogen responsible for bacterial
rot of onions (Burkholder, 1950). In their seminal taxonomic study
published in the 1960s, Stanier and colleagues (1966) noted the
extraordinary metabolic versatility of another novel pseudomonad for
which they proposed the name P. multivorans. This novel species was
mainly isolated from soil and water samples. A few years later
Ballard and co-workers (1970) reported on the synonymy between P.
cepacia and P. multivorans. Nomenclatural priority was given to the
former, as this was the oldest validly described species. In the
same year, Jonsson (1970) proposed the name Pseudomonas kingii for
CDC group EO-1 (eugonic oxidizer group 1), an opportunistic human
pathogen. Subsequent taxonomic analyses (Snell et al., 1972 ;
Samuels et al., 1973 ; Sinsabaugh and Howard, 1975) again revealed
that this novel organism was the same as P. cepacia. Thus, already
in the early 1970s, it was obvious that P. cepacia was a plant
pathogen and an opportunistic human pathogen with soil and water as
natural reservoirs. The name P. cepacia was not included in the
Approved list of Bacterial Names and therefore lost standing in
bacterial nomenclature until 1981, when it was revived by Palleroni
and Holmes.
The taxonomic heterogeneity of the genus Pseudomonas was revealed by
the work of Palleroni and co-workers and led to the gradual
dissection of the genus over the following decades. In 1992, P.
cepacia and several other species of rRNA group II sensu Palleroni
et al. (
Pseudomonas solanacearum, Pseudomonas pickettii, Pseudomonas
gladioli, Pseudomonas mallei, Pseudomonas pseudomallei and
Pseudomonas caryophylli) were transferred to the new genus
Burkholderia (Yabuuchi et al., 1992). Unlike the genus Pseudomonas,the genus Burkholderia belongs to the beta-subdivision of the
Proteobacteria (Kersters et al., 1996). In a subsequent study,
Yabuuchi et al. (1995) reclassified two of these Burkholderia
species, B. solanacearum and B. pickettii, and Alcaligenes
eutrophus, into the novel genus Ralstonia (Yabuuchi et al., 1995).
Over the past ten years, the interest in
B. cepacia - like organisms
led to the discovery and description of a multitude of novel species
which are mainly of environmental origin. The genus now contains
following 26 species: Burkholderia andropogonis, Burkholderia
ambifaria, Burkholderia anthina, Burkholderia caledonica,
Burkholderia caribensis, Burkholderia caryophylli, B. cepacia
(genomovars I, III and VI), Burkholderia fungorum, Burkholderia
gladioli, Burkholderia glathei, Burkholderia glumae, Burkholderia
graminis, Burkholderia kururiensis, Burkholderia mallei,
Burkholderia multivorans, Burkholderia phenazinium, Burkholderia
plantarii, Burkholderia pseudomallei, Burkholderia pyrrocinia,
Burkholderia sacchari, Burkholderia stabilis, Burkholderia
thailandensis, Burkholderia ubonensis, and Burkholderia
vietnamiensis.
The B. cepacia complex.
In the early 1990s the lack of sensitivity and specificity of
various identification approaches for B. cepacia were reported (e.g.
Kiska et al., 1996). Other studies described the presence of hybrid
strains with characteristics intermediate between those of typical
B. cepacia and B. gladioli,
another well-known plant pathogen(Simpson et al., 1994). These data, together with the striking
differences in clinical outcome, transmissibility, and pathogenic or
beneficial behaviour towards plants, might all have been related to
strain specific characteristics but could also have pointed to an
underlying taxonomic problem.
To verify the latter possibility, a polyphasic taxonomic study was
initiated 1992, at the Laboratorium voor Microbiology of the Faculty
of Sciences (University of Ghent, Belgium). A first study, published
in 1997, dealt with some 80 B. cepacia-like organisms and revealed
that B. cepacia isolates, cultured from clinical or environmental
sites, belonged to at least five distinct genomic species
(genomovars [Ursing et al., 1995]), referred to collectively as the
B. cepacia complex (Vandamme et al., 1997). These B. cepacia complex
species all shared a high degree of 16S rDNA sequence similarity
(98 - 99%) and moderate levels of whole-genome DNA-DNA hybridization
(30-50%) (Vandamme et al., 1997; 2000). Following identification of
distinguishing phenotypic characteristics, the name B. multivorans
was proposed for genomovar II. Genomovar V was identified as B.
vietnamiensis, an organism until then primarily isolated from the
rice rhizosphere. Following a thorough investigation of the
phenotypic and genotypic characteristics of B. cepacia genomovar IV
strains (Vandamme et al., 2000), it became obvious that this
organism could be differentiated from all other members of the B.
cepacia complex and it was formally classified and named as B.
stabilis. In the absence of differential biochemical tests to
separate genomovar III from genomovar I (for which the name B.
cepacia has to be preserved) the former genomovar remained unnamed.
The need to have a defined set of well characterised strains
representative of each genomovar, led to the delineation of an
experimental strain panel that was deposited in the Belgium
Coordinated Collections of Microorganisms/Laboratorium Microbiologie
Ghent (BCCM/LMG) bacteria collection, at the University of Ghent,
Belgium (BCCM/LMG:
www.belspo.be/bccm/). This B. cepacia
complex strain panel was composed and deposited to assist with
accurate identification, epidemiological analysis and systematic
studies of virulence on this important group of opportunistic
pathogens (Mahenthiralingam et al., 2000b).
By the mid 1990s, the cystic fibrosis community felt the need to
coordinate their efforts to study this organism and
the 'International B. cepacia Working Group was established in 1996
as "... a forum for clinicians and scientists interested in
advancing knowledge of B. cepacia infection/colonisation in persons
with cystic fibrosis through the collegial exchange of information
and promotion of coordinated approaches to research ..."
(http://go.to/cepacia). The collaborative studies with many
colleagues including Prof. Dr. J. R. W. Govan from the University of
Edinburgh (the United Kingdom Burkholderia cepacia Repository),
Prof. Dr. David P. Speert from the University of British Columbia
(the Canadian Burkholderia cepacia complex Research and Referral
Repository), Prof. Dr. John J. LiPuma from the University of
Michigan (the United States Burkholderia cepacia Research Laboratory
and Repository), and Dr. Eshwar Mahenthiralingam from the University
of Cardiff (Cardiff School of Biosciences, United Kingdom) revealed
an even more complex picture of the underestimated biodiversity of
these bacteria.
By now, up to 3000 isolates tentatively classified as 'B. cepacia'
have been examined and new identification tools have been developed
(see below). These collaborative studies revealed the presence of
various other bacterial species that are regularly misidentified as
B. cepacia (Coenye et al., 2000 and submitted; McMennamin et al.,
2000; Shelly et al., 2000). It also demonstrated that B. cepacia is
a complex of at least nine closely related organisms each
representing a distinct species.
Organisms that are regularly
misidentified as B. cepacia include well-known species such as
Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Alcaligenes
xylosoxidans, and Ralstonia pickettii, and more rare species like
Acinetobacter species, Bordetella hinzii, Comamonas testosteroni,
Chryseobacterium species, Herbaspirillum species, Moraxella
osloensis, Ralstonia gilardii, Ralstonia mannitolilytica, Rhizobium
radiobacter, Xanthomonas species, and several members of the familyEnterobacteriaceae. In addition, several novel bacteria were
identified and described amongst these isolates. These include
Pandoraea sputorum, Pandoraea pnomenusa, Pandoraea pulmonicola,
unnamed Pandoraea species, Burkholderia fungorum, and Inquilinus
limosus (Coenye et al., 2000, 2001a and submitted).
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Agricultural Use of Burkholderia (Pseudomonas) cepacia: A Threat ...In the past 2 decades, Burkholderia cepacia has emerged as a human pathogen causing numerous outbreaks, particularly among cystic fibrosis (CF) patients. ...
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