β-lactamases produced by amoxicillin-clavulanate-resistant enterobacteria isolated in Buenos Aires, Argentina: A new blaTEM gene
Revista Argentina de Microbiología
Resistance to β-lactam/β-lactamase inhibitors in enterobacteria is a growing problem that has not been intensively studied in Argentina. In the present work, 54/843 enterobacteria collected in a teaching hospital of Buenos Aires city were ampicillin-sulbactam-resistant isolates remaining susceptible to secondand third-generation cephalosporins. The enzymatic mechanisms present in the isolates, which were also amoxicillin-clavulanic acid (AMC)-resistant (18/54) were herein analyzed. Sequencing
... vealed two different variants of bla TEM-1 , being bla TEM -1b the most frequently detected allelle (10 Escherichia coli, 3 Klebsiella pneumoniae, 2 Proteus mirabilis and 1 Raoultella terrigena) followed by bla TEM-1a (1 K. pneumoniae). Amoxicillin-clavulanate resistance seems to be mainly associated with TEM-1 overproduction (mostly in E. coli) or co-expressed with OXA-2-like and/or SHV β-lactamases (K. pneumoniae and P. mirabilis). A new bla TEM variant (TEM-163) was described in an E. coli strain having an AMC MIC value of 16/8 μg/ml. TEM-163 contains Arg 275 Gln and His 289 Leu amino acid substitutions. On the basis of the high speci c activity and low IC 50 for clavulanic acid observed, the resistance pattern seems to be due to overproduction of the new variant of broad spectrum β-lactamase rather than to an inhibitor-resistant TEM (IRT)-like behavior.