Microbiological Evaluation and Identification of Yeast Isolated from Natural Juices and Refreshments Commercialized in the Gran Area Metropolitana of Costa Rica

Introduction: Yeast are microorganisms strongly related to the spoilage of natural juices.  Besides this spoilage capacity, the presence of Candida pathogenic species in natural juices has also been reported.  It is important to evaluate the presence of yeast in this type of product as well as their potential resistance to fluconazole.

Purpose: to isolate, identify and determine the susceptibility to fluconazole of yeast present in pasteurized or not fruit juices and refreshments, commercialized in the Gran Area Metropolitana of Costa Rica.

Methods: 50 samples of fruit juices and refreshments (100 non-pasteurized and 50 pasteurized) were analyzed.  To each sample, a measure of pH and Brix grades was performed. Also, the Most Probable Numer (MPN) of total and thermotolerant coliforms, Eschericihia coli and Staphylococcus aureus was performed.   

Yeast were quantified using oxytetracicline glucose yeasts extract agar (OGYE) incubated at 25°C for 5 days.  Vitek 2 system was used for yeast identification.  (BioMéreiux, France)  Fluconazole resistance was determined by the broth microdilution method proposed by the European Committee of Antimicrobial Susceptibility Testing (EUCAST).

Results: pH ranged between 2.80 and 6.61 for non-pasteurized juices, and between 2.52 and 5.14 for pasteurized ones.  Most non-pasteurized juices (58%) had a range between 5.1 and 10 Brix grades, meanwhile the pasteurized ones between 10.1 and 15.  15% of non-pasteurized juices presented E. coli and non-sample was positive for S. aureus.  78% of pasteurized  juices presented yeast counts under 10² CFU/mL, contrasting with 57% of non-pasteurized juices that presented yeast count between 10² and 10⁵ CFU/mL.  Candida  was the predominating genre isolated from pasteurized juices.

Significance: the microorganisms levels present in non-pasteurized juices are very high, partially due to a deficiency in hygienic practices.  The isolation of Candida as the most frequent genre agrees with literature reports.  Non strain was resistant to fluconazole, these bacteria come from natural environments and  have not been exposed to  selective pressure that might favor the development of resistance.