Abstract
The resistance phenotype of the clinical isolate of
Escherichia coli
1941 was characterized by high-level resistance to penicillins and to combinations amoxicillin-ticarcillin/clavulanate and ampicillin/sulbactam.
This resistance was carried by the conjugative plasmid pEC1941 that encoded a
β
-lactamase activity. The purified enzyme focused at pI 5.4 and was strongly inhibited
in vitro
by clavulanic
acid (IC
50
= 0.09
μ
M). Nucleotide sequence analysis revealed identity between the plasmid borne
bla
TEM
gene of
E. coli
1941 and the
bla
TEM-1B
gene, except for a single C-to-T substitution at position 32 in the promoter region leading to the overlapping promoters
Pa
and
Pb
. No alterations in the expression of outer membrane porins
OmpC and OmpF have been detected. These findings show that the resistance of
E. coli
1941 to the combinations of
β
-lactams with
β
-lactamase inhibitors is related to high-level
production of TEM-1 enzyme expressed from the strong promoters
Pa
and
Pb
.