Incidence of strains producing extended spectrum beta-lactamases in Argentina.

The incidence of strains producing transferable beta-lactamases capable of hydrolyzing third generation cephalosporins or aminothiazole-oximino substituted monobactams in five Buenos Aires hospitals during a four month period was studied. These enzymes were categorized by 1) MIC greater than or equal to 1 mg/l for third generation cephalosporins; 2) MIC less than 0.06 mg/l for third generation cephalosporins combined with clavulanic acid or sulbactam; 3) sensitivity to imipenem or cephamycins (excluding permeability mutants); and 4) transferable resistance by conjugation. Beta-lactamases hydrolyzing aminothiazole-oximino substituted monobactams were produced by 17.2% of Enterobacteriaceae from intensive care unit patients; 3.6% from inpatients of other units and 1.2% from outpatients. Producers were mainly Klebsiella spp. (45/46) resistant to aminoglycosides (most of them AAC 3'-AAC 6' producers). Three strains had a an isoelectric point of 6.0, two of 6.5 and three of 7.7. TEM-1 beta-lactamase (isoelectric point 5.4) was detected in 6/8 strains. An inocolum effect was observed in 40/46 strains. A Klebsiella pneumoniae strain preserved since 1982 also produced a transferable beta-lactamase hydrolyzing aminothiazole-oximino substituted monobactams.