CAO THI BAO
VAN1,3 , THIERRY LAMBERT 1,2 ,
PATRICE COURVALIN 1
1 Unité des Agents
Antibactériens, Institut Pasteur ,
2 Centre d’Etude Pharmaceutiques, Châtenay–Malabry, France, 3
Institut Pasteur d’Ho Chi Minh Ville, Viet Nam.
Resistance of Klebsiella pneumoniae BM4493 isolated in
Ho Chi Minh City in Vietnam,
to cefotaxime and aztreonam was due to production of the novel CTX-M-17 b-lactamase.
The blaCTX-M-17 gene was
borne by the 7,086-bp pIP843 plasmid which was entirely sequenced and belonged
to the ColE1-family. The 876-bp blaCTX-M-17
differed from blaCTX-M-14 by
two nucleotides that led to the single amino acid substitution Glu289®Lys.
The blaCTX-M-17 gene was
flanked upstream by a ISEcp1-like element and downstream by an IS903-variant designated IS903-C.
The transcriptional start site of blaCTX-M-17
was located 109 nucleotides upstream from the initiation codon in the ISEcp1-like element, which also provided
the promotor sequences. Plasmid pIP843 contained 5 ORFs transcribed in the same
orientation. Regions homologous to sequences coding for
putative RNAII, RNAI transcripts and a to a rom
gene, involved in regulation of transcription and of stability of ColE1-like
plasmids were identified. Consensus sequences for putative replication origin (oriV) and transfer (oriT) origins were present.
Results of a transposition assay and of primer extension experiments indicate
that ISEcp1 can contribute to
dissemination of blaCTX-M-17 and
also provides the promoter for expression of this gene.
The CTX-M enzymes represent a new
family of class A extended-spectrum ß-lactamases
(ESBL). The first member, MEN-1 (CTX-M-1), was reported at the beginning of the
1990s (3, 4). In contrast to TEM and SHV type cefotaxime-hydrolyzing ESBLs, CTX-M ß-lactamases are much more active against
cefotaxime as a substrate than against ceftazidime. This probably results from
changes in amino acids critical for extended-spectrum activity (3, 15, 18, 22).
To date, the fast growing CTX-M
family comprises 14 members: CTX-M-1 (MEN-1) (3, 4), CTX-M-2 (5), CTX-M-3 (16),
CTX-M-4 (13), CTX-M-5 (7), CTX-M-7 (previously designated CTX-M-5) (14),
CTX-M-8 (6), CTX-M-9 (31), CTX-10 (27), CTX-M-13, 14, 15 (accession no. AF252621, AF252622, AF252623, unpublished data), Toho-1 (19), and
Toho-2 (22). These enzymes have been mainly found in Escherichia coli and Salmonella isolated from South
America (5), Eastern Europe (7, 16), and Japan
(19, 22). Little is known about the environment of the structural genes for
these enzymes and their promoters have not been identified experimentally.
Numerous bla genes have been found located on plasmids and some of them are
part of transposons or constitute cassettes in integrons (23, 29). The aim of
this work was to characterize the CTX-M-type ß-lactamase from Klebsiella pneumoniae BM4493 isolated in
Viet Nam, which
was resistant to cefotaxime and apparently susceptible to ceftazidime, and to
identify its genetic basis.