A New Method for Antibiotic Sensitivity Testing of Bronchial Flora

¹ Bacteriologist, East Tennessee Children's Hospital, and Chemical-Medical Laboratories.
² Attending Thoracic Surgeon, Fort Sanders Presbyterian Hospital, and University of Tennessee Memorial Research Center and Hospital.
³ Professor of Bacteriology, University of Tennessee.

1. A new Direct Dilution Method, which is more rapid and permits a more accurate evaluation of drug effectiveness, is described for the sensitivity testing of bronchial flora. The steps of the procedure are as follows: (a) Homogenize one part of bronchial secretions with three parts 5 per cent dextrose water. Amounts may be varied depending on the viscosity of the secretions. (b) Incorporate up to 10 cc.'s of homogenate into 125 cc.'s of tryptose blood agar base containing 5 cc.'s of defibrinated blood at a temperature of 45° C. (c) Mix well and distribute into petri dishes (six for above amount). Allow to solidify and apply test discs ("Multidiscs"—Case Laboratories). (d) Incubate at 37° C. and read at 4, 12 and 24 hours. (e) Measure from the periphery of the test disc to the initial growth zone and report in mm. The reading is based on the visible indications of bacterial metabolism in the media (i.e., hemolysis, turbidity, etc.).

2. The method overcomes certain disadvantages encountered in routine methods of testing and has been found to be as economical for the patient as methods currently employed.

3. The data presented would indicate that penicillin is still a highly effective antibiotic in the treatment of respiratory infections.

4. Careful clinical observations have tended to corroborate the accuracy of the laboratory results.