Gram stain and culture of morning and 24 h sputum in the diagnosis of bacterial exacerbation of chronic bronchitis: a dogma disputed

Abstract

Bacteriological results from microscopic and cultural examinations of morning and 24 h sputum were compared in an attempt to optimize the diagnosis of bacterial exacerbations of chronic bronchitis. Twelve patients collected sputum randomly on two consecutive days, either fresh morning sputum (3 h sputum) first, followed by 24 h sputum or vice-versa. Sputa were washed three times in 0.9% NaCl and then examined microscopically before and after homogenization with 2% pancreatin. Cultural examinations were performed on homogenized sputum. Haemophilus influenzae, pneumococci and neisseriae were identified more often in Gram stains than in cultures; staphylococci and Gram-negative rods less frequently so. About 50% of organisms microscopically identified as pneumococci failed to grow in cultures. Microscopic examinations revealed a marked reduction of cells and bacteria after homogenization with pancreatin. Gram stains of 24 h sputum show comparable results to those of morning sputum. No differences were found in cultures. Microscopic examination of the Gram stains was found to be superior to cultural examination. The value of microscopic examination was impaired by the addition of pancreatin.