Abstract

DI CONZA, José A et al. ß-lactamases produced by amoxicillin-clavulanate-resistant enterobacteria isolated in Buenos Aires, Argentina: A new bla_TEMgene. Rev. argent. microbiol. [online]. 2014, vol.46, n.3, pp.210-217. ISSN 0325-7541.

Resistance to ß-lactam/ß-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 second-and third-generation cephalosporins. The enzymatic mechanisms present in the isolates, which were also amoxicillin-clavulanic acid (AMC)-resistant (18/54) were herein analyzed. Sequencing revealed two different variants of blaTEM-1, being bla_TEM-1bthe 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 ß-lactamases (K. pneumoniae and P. mirabilis). A new bla_TEMvariant (TEM-163) was described in an E. coli strain having an AMC MIC value of 16/8 µg/ml. TEM-163 contains Arg₂₇₅Gln and His₂₈₉Leu amino acid substitutions. On the basis of the high specific activity and low IC50 for clavulanic acid observed, the resistance pattern seems to be due to overproduction of the new variant of broad spectrumß-lactamase rather than to an inhibitor-resistant TEM (IRT)-like behavior.

Keywords : Amoxicillin-clavulanate resistance; TEM-163; Enterobacteria; TEM-1 overproduction.

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