Honors College

Document Type

Honors Thesis

Publication Date



Mastitis is an inflammation of the mammary gland that costs the United States dairy industry between $1.7 and $2 billion annually [9]. Approximately 97% of mastitis infections are caused by bacteria, which can be treated with antibiotics [2]. However, mastitis infections can be caused by the alga, Prototheca. Specifically, it is P. zopfii (genotype 2) and P. blaschkeae that have been found in cows with mastitis [7]. There are currently no approved treatments for protothecal mastitis. The following experiments a tested the effects of grapefruit seed extract (GFSE) on P. zopfii (genotype 2) using spectrophotometry and plating techniques. GFSE was chosen because previous research has shown it has antimicrobial properties, it is water soluble, inexpensive, and has the potential to be a legal treatment. Prototheca isolation medium (PIM) broth was inoculated with P. zopfii colonies to 47% transmittance (T). Serial dilutions of GFSE were made 1:1 with distilled water (DW) starting at 4,000ug/mL down to 125ug/mL. These dilutions were mixed 1:1 with 47% PIM and incubated for 72 hours. Absorbance readings were taken at 0, 24, 48, and 72 hours, and the samples plated on blood agar to evaluate the sterility of the samples.It was found that not even the highest concentration of GFSE was effective at inhibiting the P. zopfii (G2) colonies. However, this study does not preclude that GFSE may be effective against P. zopfii growth under different conditions.