Novel blaTEM-positive ampicillin-susceptible strains of Haemophilus influenzae

Two ampicillin-susceptible strains of Haemophilus influenzae were found to carry blaTEM genes. In one strain ampicillin susceptibility was explained by poor expression of a functional TEM-1 enzyme from a putative weak promoter created by a mutation in the promoter region of the gene, and in the other by production of an inactive mutant TEM enzyme.