Prepared by:
Nam Sun Wang
Department of Chemical Engineering
University of Maryland
College Park, MD 20742-2111

Introduction

In microbiological and biochemical engineering studies, one almost always deals with a pure culture or a mixture of known cultures, except perhaps in wastewater treatment studies. Unless aseptic culture techniques are followed strictly, an originally pure culture will definitely become contaminated with other unwanted species. For illustrative purposes, an extraterrestrial who has never seen a human being simply cannot accurately study human behavior if the group of subjects to be observed includes, in addition to humans, monkeys, dogs, cats, and many more other "contaminants." The results of such a study will certainly be unreliable. Similarly, the use of a contaminated culture with unknown microorganisms will only lead to incredible results that are of little value. Thus, the isolation and maintenance of a pure culture is of utmost importance in many microbiological studies.

It is especially important to work with a well characterized strain if the microorganism is used for food preparation, as well as in antibiotic production where the product is to be taken internally. For the same reason that a student will not lick an incubated plate that was exposed to the air, the presence of a large number of contaminants may present a potential health hazard, especially when the exact natures of the contaminants are unknown. Licking that agar plate probably will not kill the student; however, the probability of fatality certainly increases with higher numbers of organisms. Conversely, the probability of a wasted fermentation run due to contamination is directly proportional to the number of microorganisms in the environment, which in turn is directly related to the cleanliness of the laboratory.

The need for a clean working environment in biochemical engineering studies must be stressed again, for cleanliness is the prerequisite to any meaningful work. (This obsession is not the result of the instructor having had bad toilet training as Sigmund Freud may have concluded.) As demonstrated by the plate transfer process, many parts of the aseptic procedures require occasional exposure to the surrounding environment. Since our laboratory cannot be made totally sterile economically, it is imperative that the room be kept clean. The use of a laminar hood, which creates an air curtain to reduce the chance of contaminants drifting into the working space enclosed by the hood, is highly recommended if it is available. However, a laminar hood itself must still be maintained in a clean condition.

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