Inhibition of Bacillus cereus Strains by Antimicrobial Metabolites from Lactobacillus johnsonii CRL1647 and Enterococcus faecium SM21

Abstract

Bacillus cereus is an endospore-forming, Gram-positive bacterium able to cause foodborne diseases. Lactic acid bacteria (LAB) are known for their ability to synthesize organic acids and bacteriocins, but the potential of these compounds against B. cereus has been scarcely documented in food models. The present study has examined the effect of the metabolites produced by Lactobacillus johnsonii CRL1647 and Enterococcus faecium SM21 on the viability of select B. cereus strains. Furthermore, the effect of E. faecium SM21 metabolites against B. cereus strains has also been investigated on a rice food model. L. johnsonii CRL1647 produced 128 mmol/L of lactic acid, 38 mmol/L of acetic acid and 0.3 mmol/L of phenyl-lactic acid. These organic acids reduced the number of vegetative cells and spores of the B. cereus strains tested. However, the antagonistic effect disappeared at pH 6.5. On the other hand, E. faecium SM21 produced only lactic and acetic acid (24.5 and 12.2 mmol/L, respectively) and was able to inhibit both vegetative cells and spores of the B. cereus strains, at a final fermentation pH of 5.0 and at pH 6.5. This would indicate the action of other metabolites, different from organic acids, present in the cell-free supernatant. On cooked rice grains, the E. faecium SM21 bacteriocin(s) were tested against two B. cereus strains. Both of them were significantly affected within the first 4 h of contact; whereas B. cereus BAC1 cells recovered after 24 h, the effect on B. cereus 1 remained up to the end of the assay. The LAB studied may thus be considered to define future strategies for biological control of B. cereus.

Characterization of the microbial community in three types of fermentation starters used for Chinese liquor production

“…faecium in Fuqu require further investigation. Soria and Audisio verified that the presence of E . faecium could inhibit the growth of B .…”

Antagonistic effects of Bacillus subtilis subsp. subtilis and B. amyloliquefaciens against Macrophomina phaseolina: SEM study of fungal changes and UV-MALDI-TOF MS analysis of their bioactive compounds

“…6 concentrations of about 1 x 10 7 cells per mL and 1 x 10 5 spores per mL were obtained. For spore concentration measurement we proceeded according to Soria and Audisio (2014). Briefly, the cellular suspension was warmed up for 10 min at 80º C and then kept for 1 h at 8 °C.…”

Laboratory evaluation of Lactobacillus johnsonii CRL1647 metabolites for biological control of Musca domestica

“…Thus, we contend that the chemical nature of the acids involved in each case must be crucial. In acidic solutions, organic acids are more powerful at generating biological (antibacterial and antifungal) effects because of the prevalence of undissociated species; in fact, they are the ones that effectively exert the biological action, as is well documented (Ogawa et al, 2001;Makras et al, 2006;Ger ez et al, 2010;Soria & Audisio, 2014). By considering reported values for the acidity constants of the organic acids involved (Ger ez et al, 2010), we can estimate that in the larval diet treated with the CFS from L. johnsonii CRL1647, at pH 4.1, the percentages of the undissociated species are: 35, 83, and 19 for lactic, acetic, and phenyllactic acid, respectively.…”