A batch culture is grown in a closed system. The medium may be solid or liquid, contained in a Petri dish, test tube, flask or fermenter, and may or may not be accessible to sterile air. Samples may be taken from the culture at intervals. However, there is no continuous addition of fresh medium with a corresponding continuous removal of an equal volume of spent medium containing organisms. This latter procedure is continuous culture, and will be considered in the next chapter.

Usually the inoculum will be a pure culture, that is, organisms believed to be all of the same kind, such as Escherichia coli or Staphylococcus epidermidis. The object will be to study some property of a particular strain. Sometimes the inoculum may be an unknown mixture of organisms, like soil or pus. In these cases, the object will be to find out what organisms were present in the inoculum, and perhaps to go on to isolate some of these as pure cultures.

Assessment of growth

Often all that is wanted is a ‘yes’ or a ‘no’ answer. Looking at a culture after incubation is then enough.