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Antimicrobial Agents and Chemotherapy, April 1999, p. 969-971, Vol. 43, No. 4
Service de Microbiologie,
Received 22 July 1998/Returned for modification 3 November
1998/Accepted 3 January 1999
The sequences of the blaTEM genes encoding
TEM-20, TEM-21, TEM-22, and TEM-29 extended-spectrum Extended-spectrum
We report the sequence of the structural genes for TEM-20, TEM-21,
TEM-22, and TEM-29 and of the promoters of the genes encoding TEM-20,
and TEM-22. The strains used were E. coli J53-2 (pUD30, TEM-20) (5), E. coli J53-2 (pUD31, TEM-21)
(5), E. coli HB101 (TEM-22) (4) and
the clinical isolate E. coli DEL (TEM-29) (3).
PCR amplification of the blaTEM genes was
performed using primers OT3 and OT4 (3) corresponding to
positions 209 to 228 and 1047 to 1066, respectively, of the
blaTEM-1 gene (26), which allow the
amplification of the entire coding region. Both strands of the PCR
products were sequenced (21) using the PCR primers, fluorescent dye-labeled dideoxynucleotides, thermal cycling with Taq polymerase, and an ABI 373A DNA sequencer (Applied
Biosystems, Foster City, Calif.). In case of differences in the
sequences obtained for the two strands, a PCR product obtained
independently was subsequently sequenced. PCR amplification and DNA
sequencing of the promoter and coding regions of the
blaTEM-20 and blaTEM-22 genes were performed as described (16).
The BLASTN (1) program at the National Center for
Biotechnology Information was used for database searches, and the
Clustal V program (11) was used to align multiple protein
sequences. The EMBL accession numbers for the nucleotide sequences are
Y17581 for blaTEM-20, Y17582 for
blaTEM-21, Y17583 for
blaTEM-22, and Y17584 for
blaTEM-29. The changes in the genes are shown in
Table 1, and those in the deduced amino
acid sequences are shown in Table 2.
The sequence of blaTEM-20 revealed that this
gene was derived from the blaTEM-2-like
group (silent mutations of blaTEM-2 and C
at position 317) (7) whereas we proposed, following
PCR-RFLP, that TEM-20 was derived from TEM-1 (3). Two
mutations, T747 Analysis of the sequence of blaTEM-21 showed
that this gene derived from blaTEM-2 (A at
position 317). The deduced TEM-21 protein had the same
substitutions responsible for resistance to broad-spectrum
cephalosporins and aztreonam as TEM-3 (24) and
TEM-4 (derived from TEM-1) (25). The enzyme had a
His-153 blaTEM-22 differs from
blaTEM-3 by a C The sequence of blaTEM-29 showed that this
gene was derived from blaTEM-1B and differed by
a silent mutation, T226 Our results confirm that sequencing is the only truly definitive method
for DNA analysis, even if PCR-RFLP is a useful approach for
epidemiological studies.
Analysis of the promoter regions of blaTEM-20
and blaTEM-22 indicated that
blaTEM-22 had the same T-for-C change at
position 32 as that observed in Tn1,
blaTEM-3, blaTEM-4, and
blaTEM-5 (Fig. 1) (24, 25). This change
converts the weak P3 promoter of blaTEM-1 (Tn3) into the two
overlapping Pa + Pb promoters and results in
a large increase in
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Sequences of the Genes for the TEM-20, TEM-21,
TEM-22, and TEM-29 Extended-Spectrum
-Lactamases
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ABSTRACT
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Abstract
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-lactamases
were determined. Analysis of the deduced amino acid sequences indicated
that TEM-20 and TEM-29 were derived from TEM-1 and that TEM-21 and
TEM-22 were derived from TEM-2. The substitutions involved were Ser-238 and Thr-182 for TEM-20; His-164 for TEM-29; Lys-104, Arg-153, and
Ser-238 for TEM-21; and Lys-104, Gly-237, and Ser-238 for TEM-22. The
promoter region of the blaTEM-22 gene was
identical to that of blaTEM-3. High-level
production of TEM-20 could result from a 135-bp deletion which combined
the
35 region of the Pa promoter with the
10 region of
the P3 promoter and a G
T transition in the latter motif.
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TEXT
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Abstract
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-lactamases TEM-20 and TEM-21 were detected in two nosocomial
Klebsiella pneumoniae strains isolated in Tunis, Tunisia, in
1986 and 1988, respectively (5). A high level of resistance
to cefotaxime, ceftriaxone, ceftazidime, and aztreonam was observed for
both strains. TEM-20 and TEM-21 showed hydrolysis rates for cefotaxime
and ceftriaxone similar to those of TEM-3 (22) and TEM-4
(18). In contrast to TEM-20, TEM-21 showed a significant
rate of ceftazidime hydrolysis that was similar to those of TEM-3
(22) and TEM-4 (18). Isoelectric point
determination (5.4 for TEM-20 and 6.4 for TEM-21) and hybridization
studies led to the designation of the enzymes (5). Point
mutations in the corresponding structural genes detected by
PCR-restriction fragment length polymorphism (RFLP) (3)
indicated the following substitutions in the deduced amino acid
sequences. TEM-20 had a Glu at position 104 as in TEM-1 and the same
amino acid substitution, Ser-238 for Gly, as in TEM-19 (6, 12,
15), but the corresponding gene differed from the
blaTEM-19 gene by a G
A transversion at position 925. TEM-21 was derived from TEM-2 and had the same
substitutions enhancing the substrate spectrum as TEM-3 and TEM-4 but
differed from TEM-3 by an additional substitution (His-153 for Arg),
resulting in a pI difference (6.4 versus 6.3). TEM-22 (pI 6.3) from a
K. pneumoniae clinical isolate was previously characterized
by biochemical analysis only (4). Donor, transconjugant, and
transformant strains producing this enzyme have a higher level of
resistance to aztreonam than to ceftazidime and cefotaxime
(4). This very unusual resistance phenotype led to the
designation TEM-22. TEM-29 (pI 5.4) from three Escherichia
coli clinical strains isolated in 1987 was reported in 1995 (3).
TABLE 1.
Nucleotide substitutions among the
blaTEM genes from Tn1
(blaTEM-2), Tn2
(blaTEM-1B), and Tn3
(blaTEM-1A) and those encoding TEM-3, TEM-20,
TEM-21, TEM-22, and TEM-29
TABLE 2.
Amino acid substitutions in TEM-type
-lactamases
C and G914
A, resulting in
amino acid substitutions Met-182
Thr and Gly-238
Ser, were found.
Substitution Ser for Gly at position 238 has been observed in TEM-19
(12) and TEM-25 (8) and extends the substrate
profile of the enzyme to cefotaxime (14), as for TEM-25
(19). Similar levels of resistance to expanded-spectrum cephalosporins were observed in the clinical strains producing these
enzymes. The second substitution (Thr for Met at position 182) in
TEM-20, which was not detected by PCR-RFLP (3),
distinguished the enzyme from TEM-19 and TEM-25. The same substitution
occurs in TEM-32 (IRT-3), TEM-43 (6), and TEM-52
(20). Alone, this substitution does not seem to extend the
substrate profile; however, when combined with Lys-104 and Ser-238,
Thr-182 confers moxalactam resistance, as observed for TEM-52
(20).
Arg substitution recently found in a TEM-21
produced by a clinical isolate of Morganella morganii
(27). The consequence of this substitution on the catalytic
activity of the
-lactamase is unknown and possibly insignificant
since residue 153 is far from the
-lactam binding site
(13).
G mutation at position 912 leading to a Gly for Ala substitution at position 237, probably involved in the high-level aztreonam resistance of the host.
Replacement of Ala-237 by threonine, as in TEM-5 and TEM-24
(6), increases the affinity of the enzyme for
extended-spectrum
-lactams (14). Replacement by saturated
mutagenesis of Ala-237 by Asp or Thr but not by Gly increases the
catalytic activity of TEM-1 against cephems (10). The effect
of these substitutions on the catalytic efficiency against aztreonam
has not been studied.
C, as in blaTEM-1A. An additional mutation,
G693
A (also detected by PCR-RFLP) (3), leads
to the amino acid substitution His for Arg at position 164, which
increases ceftazidime resistance (14). However, Ser for Arg
is the most common substitution at this position in TEM variants from
clinical isolates (6). The Gly-for-Arg substitution confers
ceftazidime resistance in TEM-1 mutants obtained by random mutagenesis
(17). In clinical isolates, this substitution is rarely
observed alone, except for TEM-11 (CAZ-lo) derived from TEM-2
(28). The low-level resistance to ceftazidime resulting from
this substitution may account for the difficulty in detecting such variants.
-lactamase production (9). There was
a 135-bp deletion in the promoter region of
blaTEM-20. This deletion was associated with a
point mutation, T for G in the
10 region of P3, leading to
greater similarity to the consensus promoter sequence, as previously
observed for blaTEM-1 in Shigella flexneri (23). Combination of the deletion and the
mutation, leading to the association of the
35 region of
Pa with the more efficient
10 region of P3, may
account for high-level resistance to oxyiminocephalosporins of the
strain producing TEM-20 due to high-level enzyme production
(5).

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FIG. 1.
Promoter sequence of the
blaTEM-20 and blaTEM-22
genes. The differences in the promoter region of Tn2 are
shown in bold and numbered according to Sutcliffe (26). The
35 and
10 regions of Pa, Pb, and
P3 are boxed. The start codon is underlined. Deleted
nucleotides are indicated by dashes.
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FOOTNOTES |
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* Corresponding author. Mailing address: Service de Microbiologie, Hôpital Saint-Louis, 1, Av. Claude Vellefaux, 75475, Paris Cedex 10, France. Phone: (33) (1) 42 49 93 48. Fax: (33) (1) 42 49 92 00. E-mail: guillaume.arlet{at}tnn.ap-hop-paris.fr.
Present address: Service de Microbiologie, Hôpital Cochin,
75014 Paris, France.
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