Mechanisms of reduced susceptibility to amoxycillin-clavulanic acid in Escherichia coli strains from the health region of Tortosa (Catalonia, Spain).
This study investigated the mechanisms involved in reduced susceptibility to amoxycillin-clavulanic acid and the prevalence of enzymes compatible with inhibitor-resistant TEM (IRT) beta-lactamases produced by Escherichia coli isolates from patients in north-eastern Spain. The resistance mechanisms of 158 strains showing resistance or intermediate resistance to amoxycillin-clavulanic acid among 1122 ampicillin-resistant clinical isolates of E. coli were assessed on the basis of their beta-lactam resistance phenotypes. beta-Lactamases produced by strains showing resistant phenotypes suggestive of inhibitor-resistant penicillinase production were characterised by their isoelectric point. Specific activity and the concentration of clavulanic acid required to inhibit beta-lactamase activity by 50% (IC50) were determined in strains harbouring enzymes that focused at pI 5.2 or 5.4 in order to achieve presumptive identification of IRT beta-lactamases. Resistance phenotypes were consistent with overproduction of TEM-1, TEM-2 or SHV-1 beta-lactamases in 56 strains, with AmpC cephalosporinase hyperproduction in 46 strains, and with production of inhibitor-resistant penicillinases in 49 strains. Of the latter isolates, 17 produced moderately high or high levels of enzymes co-focusing with TEM-1, 17 produced enzymes co-focusing with OXA-1 (n = 12) or with PSE-1 (n = 5), either alone or in association with TEM-1, while only 15 produced enzymes with a phenotype characteristic of IRT beta-lactamases. It was concluded that resistance to amoxycillin-clavulanic acid in E. coli isolates from this area was mainly associated with presumptive overproduction of TEM-1, TEM-2 or SHV-1 beta-lactamases (46%) or of AmpC cephalosporinase (29%), while the occurrence of enzymes categorised as IRT beta-lactamases was unusual (9.5%).
Department of Clinical Analysis, Hospital de Tortosa Verge de la Cinta, Tortosa, Spain. marolgap@terra.es
M O
MO
Pérez-Moreno
M
M
Pérez-Moreno
M
M
Carulla
C
C
Rubio
A M
AM
Jardí
J
J
Zaragoza
D019980:Amoxicillin-Potassium Clavulanate Combination / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000096:biosynthesis
D019980:Amoxicillin-Potassium Clavulanate Combination; D001618:beta-Lactamases