Some Metabolic Activities of Bacteria
Microbial metabolic processes are complex, but they permit the microbiologist to distinguish
among microorganisms grown in culture. Bacteria, especially, are identified by inoculating pure,
isolated colonies into media that contain one or more specific biochemicals. The biochemical reactions
that take place in the culture can then be determined by relatively simple indicator reagents,
included in the medium or added to the culture later.
Some bacteria ferment simple carbohydrates, producing acidic, alcoholic, or gaseous
end products. Many different species are distinguished on the basis of the carbohydrates they do or
do not attack, as well as by the nature of end products formed during fermentation. Still others
break down more complex carbohydrates, such as starch. The nature of products formed in amino
acid metabolism also provides information as to the identification of bacterial species. The production
of visible pigments distinguishes certain types of bacteria.
Working with pure cultures freshly isolated from clinical specimens, the microbiologist uses
a carefully selected battery of special media to identify their characteristic biochemical properties.