[Detection of inducible beta-lactamase in sputum--clinical studies on Pseudomonas respiratory infection].

To investigate the clinical incidence of inducible beta-lactamase, we measured the beta-lactamase activity in the sputum of 5 patients with chronic respiratory tract infection due to P. aeruginosa, by using the spectrophotometric method. During the piperacillin (PIPC) therapy given twice a day with a single dose of 2-3 g, sputum samples were collected every 2 hours for 3 days, and on the second day, two grams of Cefmetazole (CMZ) was added to PIPC therapy. The antibiotics concentration of each collected sputum samples were also measured by HPLC. In one out of 5 patients, no beta-lactamase activity in sputum was detected throughout the 3 days. However in three out of 5 patients, after the addition of CMZ to PIPC, the beta-lactamase activity significantly increased 2-3 times (max: 0.03 units/ml) that on PIPC alone, and gradually decreased on the 3rd day when PIPC was given alone. Then the peak concentration of PIPC with the addition of CMZ decreased to 38-73%, compared with that of PIPC alone. These findings were supported by the fact that CMZ showed a high in vitro inducer activity against the isolates from the sputum. In the remaining one patient, high beta-lactamase activity (mean: 0.16 units/ml) and no antibiotics concentration was detected to be constant throughout the 3 days, and it was confirmed for the reason that one of the isolates constitutively produced large amounts of beta-lactamase. These results suggest that inducible and constitutive beta-lactamase would clinically cause undesirable effects in the treatment by some beta-lactams and have a possibility of indirect pathogenesis.