The authors of the study, which was published in the journal Food Microbiology, said that it is well established that soft cheese is amongst the products that pose the highest risk with regard to human listeriosis.
The researchers said that this present study, along with their previous research provides strong evidence that, in case of smear soft cheese, bacteriocin-producing lactic acid bacteria can perform efficiently to control L. monocytogenes when used as surface cultures.
Objective
The purpose of the current research, according to the scientists involved, was to investigate the antilisterial effectiveness of E. faecium WHE 81 used as culture for surface smear in Munster cheese.
E faecium WHE 81, isolated from Munster cheese has been reported to be a reputed multi-bacteriocin producer with up to four independent antimicrobial peptides produced, two of which are enterocins A and B, which are known to be effective antilisterial agents, claims the report.
Results
The researchers said that, during the ripening period, L. monocytogenes rapidly initiated growth in control samples, with counts of approximately 104 CFU g−1 on day 17 and of approximately 105 CFU g−1 on day 21.
Conversely, in the test samples limited increases or no increase at all in L. monocytogenes counts was recorded during the cheese ripening. At the term of the ripening period, L. monocytogenes often remained below enumeration levels and most of the samples analyzed were free from the pathogen, claims the study.
And, according to the published findings, the inoculation of the cheese with E. faecium WHE 81 did not result in any perceivable change in pH, fungal flora or pigmented bacteria in the cheese rind during ripening.
“In our experiments, L. monocytogenes could not initiate growth and was even eradicated in most cheeses analyzed.
“Therefore, the supplementary use of bacteriocin-producing E. faecium appears to be a promising measure to combat L. monocytogenes in an infected production line,” claim the researchers.
Mutli-bacteriocin approach
However, the scientists note that the continuous use of a bacteriocin is questionable as a primary means of food preservation as resistant Listeria mutants often occur as a result.
“In this regard, the fact that E. faecium WHE 81 could produce several bacteriocins with different structures is an interesting feature, especially since synergistic activity has been shown between enterocin A and enterocin B, two of the bacteriocins produced by this strain," claim the research team.
They argue, therefore, that the use of E. faecium WHE 81 as an antimicrobial could be considered as a mutli-bacteriocin hurdle approach, likely to be more efficient in preventing the growth of undesired bacteria than the use of a single bacteriocin producer.
Source: Food Microbiology Volume 26 Issue 1 February 2009, Pages 16-20 Published online ahead of printTitle: Smearing of soft cheese with Enterococcus faecium WHE 81, a multi-bacteriocin producer, against Listeria monocytogenesAuthors: E. Izquierdo, E. Marchioni, D. Aoude-Werner, C. Hasselmann, S. Ennahar