Bacteriologic diagnosis of respiratory tract infections

The use of the Gram stain for determination of the presence of bacteria in respiratory secretions is described. Success of the procedure depends on the use of fresh samples of high cellular quality. The Gram stain can be used to distinguish the presence (among other organisms) of Streptococcus pneumoniae, Haemophilus influenzae, Branhamella catarrhalis enterobacteria and Pseudomonas. This paper also discusses the use of sputum samples for bacteriologic culture and the value of bacterial counts in expectorated sputum, and describes the use of transtracheal aspiration and transthoracic aspiration puncture. Finally, it considers the optimum procedures for the testing of antibiotic susceptibility of presumptive pathogens isolated from the lower respiratory tract.