Microcalorimetric studies on the effects of media and environmental conditions on the growth of bacteria.

A study has been made of the effects of media and oxygen tension on the power-time (p-t) traces exhibited by cells of Klebsiella aerogenes, Staphylococcus aureus and Pseudomonas aeruginosa. The p-t traces were more complex in shape when the cells were grown in rich nutrient medium than when grown in chemically-defined glucose-limited medium. There was less waste heat and more biomass was produced during growth in nutrient broth. The oxygen tension had a profound effect on the shape of the p-t traces, and two strains of S. aureus, which differed in antibiotic susceptibility, exhibited different traces at the same oxygen tension. The thermal yield of the resistant strain was less than that of the sensitive strain. The choice of medium and the level of aeration, rather than the organism, determined the shape of the p-t trace. This has serious consequences for the proposed use of microcalorimetry as a rapid method for bacterial identification.