Synergistic bactericidal effect of nisin and phytic acid against Escherichia coli O157:H7

Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt

Dokumenter

  • Fulltext

    Forlagets udgivne version, 3,82 MB, PDF-dokument

The food industry must prevent food contamination caused by pathogenic Escherichia coli strains as they pose a severe public health threat worldwide and lead to unimaginable economic losses. In this study, the synergistic antibacterial activity in vitro of nisin and phytic acid (PA), a natural metal chelate, against 5 foodborne isolates of E. coli were evaluated by a checkerboard assay. Checkerboard assay showed that nisin and PA showed a synergistic effect (FICI <0.375) on three O157 serogroup strains and an addictive effect (0.5<FICI <0.5625) on the remaining two non-O157 serogroup strains. Then the combined bactericidal effect of these compounds against E. coli O157:H7 was investigated. Results showed the number of planktonic and biofilm cells inactivated in groups treated with a combination of 0.512 mg/mL nisin plus 1 × MIC or 2 × MIC PA was significantly higher than the sum of groups treated alone (P < 0.05). Electron scanning microscopy studies revealed that the nisin plus PA treatment had a severe effect on E. coli O157:H7, which after treatment cell morphology appeared deflated with large invaginations. The effect of nisin plus PA against E. coli O157:H7 was furthermore assessed on cold-stored beef, where a similar synergistic bactericidal effect was observed. The studies demonstrate the great potential of the food-approved nisin to control the growth of undesired E. coli pathogens in foods. We used PA to overcome the permeability barrier of the outer membrane to nisin, but other food-grade metal ion chelators such as polyphosphate most likely could be used as well.

OriginalsprogEngelsk
Artikelnummer109324
TidsskriftFood Control
Vol/bind144
ISSN0956-7135
DOI
StatusUdgivet - 2023

Bibliografisk note

Funding Information:
This work was supported by the China Scholarship Council (grant numbers 201806150025 ).

Funding Information:
Phytic acid (PA) is a plant-based component obtained from oilseeds, cereals, legumes, nuts, and pollen with a powerful chelating activity responsible for its functional properties, which has been granted Generally Recognized As Safe (GRAS) status by FDA, and in EU, it has been approved as a food additive with the E-number 391 (Bloot et al., 2021). It is used widely as a preservative in meat, fruit juice, vegetables, and other food products where its function is to serve as an antioxidant and to extend shelf life (Sun et al., 2020). Two studies (Kim & Rhee, 2016a; 2016b) reported that PA had strong bactericidal activity on planktonic and biofilm cells of E. coli O157:H7 and could destroy the integrity of the cell membrane. Zhou et al. (2019) found that PA could retard growth of E. coli ATCC 11229 by causing cell membrane dysfunction.Time-kill assays have frequently been used to study the effect of antibacterial agents, alone or in combination, against pathogens (Foerster et al., 2016). By analyzing time-kill curves, it is not only possible to obtain information about the killing kinetics, but it is also possible to compare differences in growth rate and the extent of the antibacterial activity (Shi et al., 2017). For our experiments, we used TSB as a growth substrate, which is a medium that supports good growth of E. coli O157:H7 strains. In this medium, we did not observe bactericidal activity when 0.2% PA was used with lower concentrations of nisin (data not shown), which could be due to the divalent cation content of TSB. The inhibitory activity of hydrolyzed lactoferrin is reduced in the presence of excess Ca2+ and Mg 2+, and since hydrolyzed lactoferrin, which chelates divalent cations, is less active in TSB, it has been suggested that this effect is attributed to the divalent cations in TSB (Aleksandrzak-Piekarczyk et al., 2005; Branen & Davidson, 2000). In our case, the reduced antibacterial activity observed for PA and nisin cocktails in TSB could likewise be due to insufficient chelating activity of PA, resulting in an insufficiently perturbed outer membrane, which is less permeable to nisin (Kim & Rhee, 2016a). Despite the reduced antibacterial effect observed in TSB, a clear synergistic effect between PA and nisin was, however, observed.This work was supported by the China Scholarship Council (grant numbers 201806150025).

Publisher Copyright:
© 2022 The Authors

ID: 330895959