Bacterial pneumonias--evaluation of various sputum culture methods

With an objective of improving diagnostic value of sputum in bacterial pneumonias, 50 uncomplicated 'community' acquired cases were studied using Gram staining of sputum along with bedside inoculation with/without dilution of the specimen. Gram staining of sputum samples collected before treatment revealed pneumococcal infection in 46% cases. The results were however inconclusive on samples sent by routine procedure involving logistic delay. Cultural analysis of sputum processed by three different techniques showed that bedside inoculation of sputum after dilution to be the most efficient technique yielding Streptococcus pneumoniae in 34% cases, Gram positive cocci in lesser number (20%), Gram negative rods (GNR) in 18% cases. Sputum samples processed bedside without dilution yielded a lower number of pneumococci and other Gram positive cocci (24% & 16% cases respectively). Routine processing of sputum, involving logistic delay yielded a high number of Gram negative rods (62%), indicating their overgrowth. Thus bedside inoculation of sputum after dilution coupled with direct Gram staining serves as a simple and yet valuable laboratory aid in the diagnosis of uncomplicated 'community' acquired bacterial pneumonias.