Effect of culture medium and carbon dioxide concentration on growth of anaerobic bacteria commonly encountered in clinical specimens

Abstract

Representative strains of anaerobic bacteria from human infections were used to evaluate broth media, gas mixtures, and inocula for use in developing a procedure for performing minimal inhibitory concentration antimicrobic susceptibility tests. Nine commercially available media, including two that were chemically defined, were tested. Tests were performed in atmospheres with carbon dioxide concentrations between 2.5 and 10% and also in the GasPak system (BBL) that had a disposable hydrogen-carbon dioxide generator. Growth curves on each organism grown in schaedler broth and a 5% carbon dioxide atmosphere were used to determine growth characteristics, equate time of the particular growth phases to turbidity readings, and determine the numbers of viable organisms present in the culture. Schaedler broth proved to be most advantageous in combination with an atmosphere of 5% carbon dioxide, 10% hydrogen, and 85% nitrogen. The growth curve studies yielded valuable data on the rapidity and quantity of growth under these conditions. We believe these data have provided information which can be used as the basis for developing a standardized procedure for antimicrobic susceptibility testing for anaerobic bacteria.