Influence of different culture media on the antimicrobial activity of Pediococcus pentosaceus ST65ACC against Listeria monocytogenes

Abstract

Pediococcus pentosaceus ST65ACC is a bacteriocinogenic lactic acid bacteria (LAB) isolated from Brazilian artisanal cheese that is capable of inhibiting different food pathogens, mainly Listeria monocytogenes. The production of bacteriocins can be influenced by several growth conditions, such as temperature, pH, and medium composition. This study aimed to evaluate the effect of different culture media on the production of bacteriocins and antimicrobial activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The strains were inoculated alone and in coculture in four different media: BHI broth, MRS broth, meat broth, and reconstituted skim milk (RSM) 10% (w/v). The culture media were then incubated at 37 °C for 96 h, and count analysis, pH measurement, and bacteriocin production were performed at 0, 24, 48, 72 and 96 h. L. monocytogenes was inhibited to nondetectable levels in coculture with P. pentosaceus ST65ACC in MRS broth within 96 h, consistent with the high production of bacteriocin throughout the analysis period (3,200-12,800 AU/mL). However, lower inhibitory activities of P. pentosaceus ST65ACC on L. monocytogenes Scott A were recorded in BHI, RSM, and meat broth, with low or no production of bacteriocins at the analyzed times. The composition of these culture media may have repressed the production and activity of bacteriocins and, consequently, the antagonist activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The results showed that the antimicrobial activity was more effective in MRS broth, presenting greater production of bacteriocins and less variability when compared to the other media analyzed.

Keywords: Listeria monocytogenes; Pediococcus pentosaceus; Antimicrobial activity; Bacteriocin; Pediocin.

Fig. 1

Variation of pH values during bacterial growth in BHI broth (A), MRS broth (B), meat broth (C), and reconstituted skim milk (RSM) 10% (w/v) (D). The figure represents means ± standard error, n = 3. The asterisk indicates a significant difference with the control (* p < 0.05). (T1: P. pentosaceus ST65ACC; T2: P. pentosaceus MLEV8; T3: P. pentosaceus ST65ACC with L. monocytogenes Scott A; T4: P. pentosaceus MLEV8 with L. monocytogenes Scott A; T5: L. monocytogenes Scott A alone.)

Fig. 2

Mean counts (± standard error) of P. pentosaceus ST65ACC and P. pentosaceus MLEV8 inoculated in BHI broth (A), MRS broth (B), meat broth (C), and reconstituted skim milk (RSM) 10% (w/v) (D). (T1: ST65ACC alone; T2: MLEV8 alone; T3: ST65ACC in coculture with L. monocytogenes Scott A; T4: MLEV8 in coculture with L. monocytogenes Scott A)

Fig. 3

Mean counts (± standard error) of L. monocytogenes Scott A inoculated in BHI broth (A), MRS broth (B), meat broth (C), and reconstituted skim milk (RSM) 10% (w/v) (D). (T3: in coculture with ST65ACC; T4: in coculture with MLEV8; T5: inoculated alone). Different lowercase letter indicates statistical difference (p < 0.05) between treatments, within each time