Abstract
The aim of this work was to evaluate the effect of the bacteriocins bovicin HC5 and nisin against Listeria and Staphylococcus aureus in synthetic media and in milk. Growth of Listeria monocytogenes, Listeria innocua and S. aureus was carried out at 37ºC in tryptic soy broth (TSB) and in ultra-high temperature whole milk containing bovicin HC5 and nisin added either individually or in combination. Concentrations above 100 AU ml-1 of bovicin HC5 or 50 AU ml-1 of nisin inhibited the growth of Listeria species in TSB. Bacteriocins at concentrations of at least 50 AU ml-1 clearly increased the lag phase, but did not prevent the growth of S. aureus. The combination of both bovicin HC5 and nisin in TSB inhibited the growth of Listeria and S. aureus Embrapa 4018 at lower concentrations than the bacteriocins added separately. Bactericidal effect against L. monocytogenes and S. aureus cells was observed when both bacteriocins were added together in milk in concentrations larger than 400 AU ml-1 of each one. The present results demonstrate that bovicin HC5 and nisin were effective against Listeria and S. aureus assessed in milk, especially when used in combination.
Highlights
Outbreaks of listeriosis resulting from consumption of dairy products contaminated with L. monocytogenes have prompted concern about the behavior of this microorganism during processing and subsequent storage of various dairy products (Silva, Almeida, Alves, & Almeida, 2003)
The present results demonstrate that bovicin HC5 and nisin were effective against Listeria and S. aureus assessed in milk, especially when used in combination
The specific growth rate of L. monocytogenes ATCC 7644 and L. monocytogenes Scott A in tryptic soy broth (TSB) was reduced in the presence of bovicin HC5 at concentrations of 10 and 50 arbitrary unity (AU) ml-1, while growth was completely inhibited in the presence of 100 and 150 AU ml-1 of this bacteriocin (Table 1)
Summary
Outbreaks of listeriosis resulting from consumption of dairy products contaminated with L. monocytogenes have prompted concern about the behavior of this microorganism during processing and subsequent storage of various dairy products (Silva, Almeida, Alves, & Almeida, 2003). L. monocytogenes, a ubiquitous foodborne pathogen, can be potentially introduced in raw milk in a dairy industry environment. Food from animal origins, such as milk, is naturally susceptible to contamination by Staphylococcus aureus, an important pathogen able to grow in a wide range of temperatures, pH and sodium chloride concentration up 15%, and able to produce enterotoxins. These toxins are thermostable and maintain their stability even after thermal treatments (Dinges, Orwin, & Schlievert, 2000; Le Loir, Baron, & Gautier, 2003)
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