Culture supernatant produced by Lactobacillus kefiri from kefir inhibits the growth of Cronobacter sakazakii

Abstract

Cronobacter sakazakii is a life-threatening foodborne pathogen found in powdered infant formula and dairy products. Kefir is a dairy probiotic product and its antimicrobial activity against C. sakazakii was reported in our previous study. To identify key microorganisms that mediate growth suppression, we tested the antimicrobial activity of culture supernatants derived from lactic acid bacteria found in kefir. Lactobacillus kefiri DH5, L. kefiranofaciens DH101, and Bifidobacterium longum 720 (a commercial probiotic strain that served as a positive control) all significantly inhibited the growth of C. sakazakii ATCC 29544, delaying the initiation of exponential growth from 3 to 9 h in the nutrient broth. Among them, L. kefiri DH5 exerted the strongest antimicrobial effects against C. sakazakii, showing bactericidal effect at the addition of 300 µl of supernatant in 1 ml of nutrient broth. Interestingly, the supernatant of L. kefiri DH5 has higher pH and lower titrable acidity than that of L. kefiranofaciens DH101, suggesting metabolites produced by heterofermentation of L. kefiri acted more effectively to antagonise the growth of C. sakazakii. In addition, the supernatant of L. kefiri DH5 induced the leakage of cytoplasmic materials including nucleic acid and proteins, suggesting L. kefiri DH5 disrupted the cellular membrane integrity of C. sakazakii. Considering that pH neutralisation reduced the L. kefiri-dependent growth suppression, it is inferred that this activity is mainly due to organic acids produced during the fermentation process.

Microbiological characterization of Gioddu, an Italian fermented milk

“…In kefir beverage, L. kefiri, together with L. kefiranofaciens, L. kefirgranum, L. parakefiri, releases exopolysaccharides with potential antioxidant, antitumor, antimicrobial, and immunomodulating properties (Prado et al, 2015), such exopolysaccharides (EPS) production is boosted by the complex symbiosis with yeasts that occur in kefir beverage. As reviewed by Slattery et al (2019), L. kefiri strains could exert inhibitory effect on the growth of a wide range of human foodborne pathogens as Pseudomonas aeruginosa, Salmonella Enteritidis, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, and Cronobacter sakazakii, this latter with particular risk to infants (Kim et al, 2018b). Moreover, a significant in vitro and in vivo cholesterol reducing activity was also reported for L. kefiri strain DH5 by Kim et al (2017).…”

Analysis of Health Benefits Conferred by Lactobacillus Species from Kefir

“…There were also significantly higher expression levels of PPAR-α, FABP4, and CPT1 in adipose tissues in HFD-DH5 mice, genes that are associated with lipid oxidation. This strain’s supernatant was also found to inhibit the growth of Cronobacter sakazakii , a pathogen with particular risk to infants, in nutrient broth [69].…”

Kefir micro-organisms: their role in grain assembly and health properties of fermented milk

“…Modulation of intestinal microbiota by kefir administration has been demonstrated in animal trials (Kim et al . , ). This impact on microbial communities might modify the metabolite profile and is expected to influence immune responses.…”