The Antibacterial and Antifungal Effects of Cranberry Fruit (Vaccinium macrocarpon), and Its Commercial Juices against Escherichia coli, Staphylococcus aureus, Proteus mirabilis, and Candida albicans

Abstract

Background: Urinary tract infections are common bacterial infections, primarily caused by Escherichia coli, and increasing antibiotic resistance has driven interest in cranberry-derived phytochemicals as potential alternative antimicrobial agents. Aims: To evaluate the antibacterial and antifungal activity of cranberry (Vaccinium macrocarpon) preparations, including aqueous extract, macerated fruit, and commercial cranberry juice cocktails, against Escherichia coli, Staphylococcus aureus, Proteus mirabilis, and Candida albicans using the Kirby–Bauer disk diffusion method. Study Design:  Laboratory-based true experimental study utilizing the Kirby–Bauer disk diffusion method. Place and Duration of Study: Main Laboratory, College of Medical Sciences, University of Guyana, Georgetown, Guyana; conducted over a 12-week period between February 2024 and March 2024. Methodology: Fresh cranberries were processed into aqueous extract and macerated fruit slurry, while three commercial juice brands (T, C, O) were used as additional treatments. Sterile 6 mm discs were impregnated with each preparation. Standardized microbial suspensions (0.5 McFarland) of the four test organisms were inoculated onto Mueller Hinton Agar. Positive controls included ciprofloxacin (5 µg) for Escherichia coli, tetracycline (30 µg) for Staphylococcus aureus, gentamicin (10 µg) for Proteus mirabilis, and ketoconazole (1%) for Candida albicans. Plates were incubated at 37°C for 24 hours (bacteria) or 48 hours (yeast). Zones of inhibition were measured in millimetres. Data were analyzed using one-way ANOVA with a significance threshold of α = 0.05. Results: All cranberry preparations showed no inhibitory effect against Escherichia coli (all zones = 6 mm, equivalent to disc diameter). Against Staphylococcus aureus and Proteus mirabilis, cranberry treatments produced inhibition zones ranging from 6–11 mm, whereas tetracycline and gentamicin produced inhibition zones of 26 mm and 25 mm, respectively. ANOVA demonstrated significant differences among treatments (P < 0.001), with cranberry preparations exhibiting lower antibacterial activity than the antibiotic controls. Only the aqueous cranberry extract inhibited Candida albicans (10–13 mm). No significant difference was observed between the aqueous extract and ketoconazole under the conditions of the in vitro assay (F(1,10) = 0.87, P = 0.37). Conclusion: Cranberry preparations exhibited selective antimicrobial activity. While ineffective against E. coli, several preparations showed mild antibacterial effects against S. aureus and P. mirabilis. The aqueous cranberry extract produced inhibition zones similar to ketoconazole under the conditions of this in vitro assay against C. albicans. Cranberry may serve as a complementary antimicrobial agent, warranting further investigation using standardized extracts and advanced antimicrobial assays.