Investigating the Effectiveness of Antibiotic Combinations Utilized in Fuel Ethanol By Jennifer Starner, Ph.D.
Bacterial infections during fuel ethanol fermentations can negatively impact the fermentation process and lower ethanol yields. Lactic acid-producing bacteria (LAB), such as Lactobacillus, Lactococcus, Weissella and Pediococcus, are a common source of contamination due to their ability to grow in the harsh conditions, low pH, high temperatures, and high concentrations of ethanol present during fermentation. LAB are problematic as they not only compete with the yeast for nutrients and ferment-
able sugars, but also produce lactic and acetic acids that influence yeast metabolism. Ultimately, untreated bacterial infections cost plants time and money. Antibiotics, such as the β-lactam antibiotic penicillin G and the streptogramin antibiotic virginiamycin, are commonly used during fermentations to control bacterial growth and support robust ethanol yields. In response to a competitive antibiotic market and increasing antibiotic resistance, antibiotic combinations, particularly combi-
nations of penicillin G and virginiamycin, have recently been employed. However, there is little evidence supporting the use of a penicillin G/virginiamycin combination treatment during fuel ethanol fermentations. When drugs such as antibiotics are applied concurrently, drug interactions must be considered. Drug interactions can be classified as additive, synergistic, or antagonistic (Figure 1). An additive interaction is when two drugs do not interact with each other and the response to the com-
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28 | ETHANOL PRODUCER MAGAZINE | OCTOBER 2021
