Infection and yield variations can cause serious problems in production work. In the early days of the antibiotics industry, infection was often a most-serious problem, sometimes halting production for months at a time. The situation greatly improved after several years' hard work, and plants now work over long periods without trouble. Infection can occasionally break out, and a brief description of the problems it creates is therefore useful.

Outbreaks of groups of low-yielding batches, lasting for periods of time, can also cause trouble. These outbreaks may be of two kinds. Firstly there are relatively small drops in yields (15–25%), probably caused by variations in technique. Secondly, very severe falls in output, to 50%, sometimes less, associated with changed metabolism, for which there is no obvious reason.

These two problems, of infection and yield variation, are difficult to deal with. A team effort between engineers and plant staff is usually needed, a microbiologist being often called in to provide an extra pair of eyes and hands, since it usually happens that the local people find the cure. The two problems, however, are often related, since falls in yield may be due to infection, and it may be necessary to decide which.

The problem of infection

The nature of infection

Infection arises from the contamination of the batches with invading microorganisms, usually bacteria. Infection may be at low or high level. The first may have little or no effect, while with a heavy infection there are serious changes in appearance, and the culture has to be discarded. In most cases, the infection is relatively low, but it is noticeable, has some effect on production, and can be confirmed by testing.