Preventing Biofilms on Meat Processing Equipment

Background

Biofilms are bacteria’s way of lumping together on surfaces which makes them harder or impossible to kill with regular sanitization methods. It has been suggested that Shiga toxin-producing E. coli’s (STEC) ability to form biofilms may be what leads to higher incidence of STEC contamination in packing plants. This team has previously shown that STEC and Salmonella species were inhibited from forming biofilms when they were cultured with some other bacteria commonly found on meat processing equipment(called meat processing bacteria or MPB). It is then possible that some metabolites produced by the MPB could inhibit or prevent biofilm formation of STEC and Salmonella.

Objectives

• To evaluate the inhibitory effects of the cell-free culture supernatant (CFS) of three bacterial strains on the biofilm formation by Shiga toxin-producing Escherichia coli (STEC) and Salmonella enterica serovar Typhimurium.

What They Did

The researchers explored how certain bacteria found on meat surfaces could affect the development of biofilms of STEC and Salmonella. Four meat plant bacteria (MPB) Aeromonas, Hafnia, Janthinobacterium and Serratia were grown in broth media and the bacterial cells were removed to make cell free supernatant (CFS). CFS was further concentrated by freeze-drying to make cell free extract (CFE). CFS and CFE were tested against five harmful bacteria strains Salmonella, E. coli O103, E. coli O121, E. coli O111, and E. coli O145 for their ability to inhibit biofilm formation. The effect was determined by comparing the cell numbers in biofilms of a pathogen co-cultured with CFS/CFE with those of the same pathogen not-treated with CFS/CFE. The genomes of MPB were also sequenced and analyzed for the presence of genes encoding products with antibacterial/biofilm activities. Gene expression studies were carried out for two MPB with the highest inhibitory activities. This was to assess whether certain genes involved in biofilm formation being overexpressed or repressed when treated with MPB CFE. CFE of these two MPB was also boiled for 10 min to determine the heat stability of the active compounds.

What They Learned

The MPB CFS had little effect of the growth of planktonic cells of the five pathogens. However, varying effect of the same MPB CFS on different pathogen strains and different MPB CFS on the same pathogen were also observed. For example, the growth of Salmonella in biofilms was inhibited by 0.85 log after 6 days incubation with Aeromonas CFS, compared to the untreated control, while the CFS from the other three MPB showed no significant effects. The Aeromonas CFS significantly inhibited the growth of cell of Salmonella and E. coli O103, but not E. coli O121, E. coli O111 or E. coli O145. These results suggest that a more concentrated form of CFS may be required to see (higher) inhibition. E. coli O145 was not a strong biofilm former and was excluded from further testing. Significant inhibition of some CFE on the growth of planktonic cultures was observed, e.g., Aeromonas CFE significantly reduced the growth of E. coli O103, E. coli O111 and E. coli O121 by up to 3 log. CFE from all MPB strains showed significant reductions in Salmonella and E. coli O103 biofilm, and the biofilms of E. coli O121 and E. coli O111 were inhibited by all except for Janthinobacterium. Greater than 5 log reduction was observed for multiple combinations. Of note, the biofilm formation of E. coli O103 or E. coli O121 was completely prevented when incubated with Aeromonas CFE for 6 days. Active compounds from Aeromonas and Hafnia were heat-stable. Expression of key biofilm-related genes (csgD and csgA) was found to be significantly repressed when pathogens were treated with MPB CFE, inhibiting biofilm formation. The findings suggest that some meat plant bacteria produce heat-stable compounds with strong antibiofilm activity, influencing bacterial communication and biofilm formation.

What This Means

Overall, the research suggests that CFS in concentrated form of these meat plant bacteria was very effective for inhibiting biofilm formation of STEC and Salmonella. The active compounds are highly likely involved in regulating apparatus involved in biofilm formation. It is also possible some compounds have antibacterial activities, from their effects on the growth of planktonic cells. Thus, the secondary metabolites can be used to develop ways to make food safer by inhibiting the development of biofilm growth of harmful bacteria.