An improved screening technique for isolation of Nocardia species from sputum specimens

Abstract

Three selective isolation media and the paraffin baiting technique were compared with conventional culture (Sabouraud dextrose agar without antibiotic supplement) for the ability to grow and detect nocardiae from simulated sputum specimens. Modified Thayer-Martin medium, incorporating vancomycin, colistin, nystatin and trimethoprim as selective agents, produced the highest recovery rate and with the greatest suppression of normal respiratory tract flora. A clinical evaluation using a screening programme devised for a busy diagnostic microbiology laboratory was performed on 1600 sputum specimens. Inoculating sputum on modified Thayer-Martin medium and extending the initial incubation period of 3 days at 35 degrees C under 10% carbon dioxide to a further 3 weeks at room temperature in a candle jar, led to the diagnoses, which otherwise would have been missed, of pulmonary nocardiosis in 3 patients and pulmonary infections due to Neisseria meningitidis, Pseudomonas cepacia, and Serratia marcescens in a further 22 patients.