| Abstract: | Two different strains of thymidine-requiring Haemophilus influenzae (thy-) were isolated from the sputum of two patients with chronic obstructive airways disease, during therapy with oral trimethoprim for the treatment of an acute exacerbation of chronic bronchitis. Both patients responded clinically. Since trimethoprim levels in sputum and serum were very low the patients were probably non-compliant. Isolates of H. influenzae prototrophic for thymidine (thy+) were isolated from both patients in remission before, at the onset of exacerbation and also within two weeks of stopping therapy. Thy- and thy+ isolates from the same patient were of identical biotype but isolates from the two patients were of different biotypes. The minimum inhibitory concentration (MIC) of trimethoprim for the thy+ isolates obtained after therapy was significantly higher than the MIC for the isolates obtained at the onset of exacerbation. Thy- isolates were further investigated and a novel mechanism of low-level trimethoprim resistance is proposed. |
