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Updated: Oct 25, 2025
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
Uninvited Guests: a Chronology of Petri Dish Contaminations
1Department of Chemical Engineering, Loughborough University, Loughborough, United Kingdom.
Abstract:
Petri dish contaminations are commonplace and personally witnessed by every microbiologist. The vast majority of such contaminations result in nothing more than annoyance following which the Petri dishes are discarded. However, a handful of incidents of contaminations have led to momentous outcomes, the most renowned of which being that perceived by Alexander Fleming on the basis of the immense number of lives saved by penicillin. Petri dish contaminations as reported upon in the literature fall broadly into two categories; those in which the contaminant caused antagonism toward the species being cultured, and those in which the contaminant was established to be a species novum. Accounts of both of these categories of contaminations are set out here.
Insights
Petri dish contamination is common, usually causing minor issues. However, rare contamination events can lead to significant discoveries, such as penicillin, impacting microbiology and medicine.
Area of Science:
- Microbiology
- Medical History
Background:
- Petri dish contamination is a frequent occurrence in microbiology laboratories.
- Most contaminations lead to discarded cultures and minor inconvenience.
Purpose of the Study:
- To review and categorize significant historical instances of Petri dish contamination.
- To highlight instances where contamination led to major scientific or medical breakthroughs.
Main Methods:
- Literature review of reported Petri dish contamination cases.
- Categorization of contamination events based on their outcomes.
Main Results:
- Contaminations are broadly categorized into two types: antagonistic interactions and the discovery of new species (species novum).
- Notable historical examples, including Alexander Fleming's discovery of penicillin, are discussed.
Conclusions:
- While often problematic, Petri dish contamination has historically been a source of significant scientific advancement.
- Understanding contamination types can inform future research and discovery.
