Two variants of transferrable extended-spectrum TEM-β-lactamase successively isolated from a clinical Escherichia coli isolate

Abstract

In a leukaemic patient presenting a septicaemia treated with ceftrazidime and amikacin, two clinical Escherichia coli isolates distinguished by their level of resistance to oxyimino-β-lactams were isolated at an interval of 24 h. The isolates were identified by biotyping and esterase electrophoretic typing and the two host strains were shown to be identical. However, each of these strains exhibited a different transferrable extended-spectrum β-lactamase. These enzymes had different p l values (5.25 and 5.58), but were both bla TEM-1 mutants. The enzyme with p I 5.25 was identical to TEM-101 (TEM-12) (serine 162 substitution). The enzyme with p I 5.58 showed an additional amino acid substitution (lysine residue instead of an arginine at position 237) and was denominated TEM-23. These data indicate that point-mutations can be successively cumulated in vivo by bla TEM mutants, leading to expression of β-lactamases with increased hydrolysis rates.