Purpose: The objective of this research was to determine the effects of blueberry juice and blueberry proanthocyanidins against C. sakazakii over 24 h at 37°C.
Methods: Overnight cultures of two C. sakazakii strains (ATCC 29004 and ATCC 29544) grown in Tryptic Soy Broth (TSB) at 37°C were washed and resuspended in phosphate buffered saline (PBS, pH 7.2). Each washed culture was individually treated with filter-sterilized commercial blueberry juice (BJ, pH 2.8), neutralized blueberry juice (BJ, pH 7), blueberry proanthocyanidins (B-PAC; 5 mg/ml), malic acid (pH 3.0), or PBS and incubated at 37°C for 30 min, 1 h, 3 h, 6 h or 24 h. After each time-point, bacteria were initially serially diluted in TSB containing 10% beef extract, further serially diluted in PBS, surface-spread plated on Tryptic Soy Agar, and enumerated after incubation at 37°C for 24 h. Treatments were replicated thrice in duplicate and data were statistically analyzed.
Results: C. sakazakii strains 29004 and 29544 were reduced to undetectable levels after 1 h from 8.25 ± 0.12 log CFU/ml and 8.48 ± 0.03 log CFU/ml, respectively with BJ (pH 2.8) or B-PAC, while malic acid showed ~1.3 log CFU/ml reduction for both strains. Reductions of ~1 and 1.50 log CFU/ml were obtained for strains 29004 and 29544, respectively, after 30 min with BJ or B-PAC. Neutralized BJ did not reduce both strains even after 24 h.
Significance: Nutritionally beneficial BJ and B-PAC show potential use for preventing and/or treating C. sakazakii infections. Further studies on their mechanism of action and in vivo studies are warranted.