Previous Article | Next Article ![]()
Antimicrobial Agents and Chemotherapy, Jun 1997, 1322-1325, Vol 41, No. 6
D Sirot, C Recule, EB Chaibi, L Bret, J Croize, C Chanal-Claris, R Labia and J Sirot
Escherichia coli GR102 was isolated from feces of a leukemic patient. It
expressed different levels of resistance to amoxicillin or ticarcillin plus
clavulanate and to the various cephalosporins tested. The double-disk
synergy test was weakly positive. Production of a beta- lactamase with a pI
of 5.6 was transferred to E. coli HB101 by conjugation. The nucleotide
sequence was determined by direct sequencing of the amplification products
obtained by PCR performed with TEM gene primers. This enzyme differed from
TEM-1 (blaT-1B gene) by four amino acid substitutions: Met-->Leu-69,
Glu-->Lys-104, Gly-->Ser- 238 and Asn-->Asp-276. The amino acid
susbstitutions Leu-69 and Asp-276 are known to be responsible for inhibitor
resistance of the IRT-4 mutant, as are Lys-104 and Ser-238 substitutions
for hydrolytic activity of the extended-spectrum beta-lactamases TEM-15,
TEM-4, and TEM-3. These combined mutations led to a mutant enzyme which
conferred a level of resistance to coamoxiclav (MIC, 64 microg/ml) much
lower than that conferred by IRT-4 (MIC, 2,048 microg/ml) but higher than
that conferred by TEM-15 or TEM-1 (MIC, 16 microg/ml). In addition, the MIC
of ceftazidime for E. coli transconjugant GR202 (1 microg/ml) was lower
than that for E. coli TEM-15 (16 microg/ml) and higher than that for E.
coli IRT-4 or TEM-1 (0.06 microg/ml). The MICs observed for this TEM-type
enzyme were related to the kinetic constants Km and k(cat) and the 50%
inhibitory concentration, which were intermediate between those observed
for IRT-4 and TEM-15. In conclusion, this new type of complex mutant
derived from TEM-1 (CMT-1) is able to confer resistance at a very low level
to inhibitors and at a low level to extended-spectrum cephalosporins. CMT-1
received the designation TEM-50.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
A complex mutant of TEM-1 beta-lactamase with mutations encountered in both IRT-4 and extended-spectrum TEM-15, produced by an Escherichia coli clinical isolate
Laboratoire de Bacteriologie-Virologie, Faculte de Medecine, Clermont- Ferrand, France.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»