• Enterococci in Food Fermentations: Functional and Safety Aspects

      Cogan, Tim; Rea, Mary; Drinan, Finbarr; Gelsomino, R. (Teagasc, 2001-04-01)
      Enterococci are natural residents of the human and animal gastrointestinal tracts; many species are also found in soil, plants and food. These organisms also form an important part of the microflora of many cheeses, especially those made in Southern Europe, where they can reach levels of 107 - 108 cfu/g. There is contradictory information on their role in flavour development in cheese with some studies showing that they have a positive effect and others a negative one. Enterococcus faecalis, Ec. faecium and Ec. durans are the important species found in cheese, though recent results from our laboratory show that Ec. casseliflavus may also be important (see below). Many of these species withstand pasteurisation. Their presence in food has been questioned because they are responsible for many nosocomial infections in hospitals. They are also promiscuous and easily transfer antibiotic resistance to other organisms and acquire resistance to vancomycin themselves. Cheddar cheese has a complex microflora and is conducive to growth of many bacteria, especially lactic acid bacteria. Enterococci are facultative anaerobes, which ferment lactose and can grow in high salt concentrations. Therefore, they should grow in cheese if they are present in the raw milk. Phenotypically they can be confused with starter lactococci. Traditionally, they are separated from lactococci by their ability to grow at 45°C and in 6.5% salt. However, these tests have serious drawbacks since some species of enterococci cannot grow at 45°C and some lactococci can grow at 45°C and in 6.5% salt. The effect of enterococci on flavour development in Cheddar cheese has not been studied to any great extent. The overall objectives of this collaborative project were to investigate the taxonomic relationships between food, veterinary and clinical isolates of enterococci, their virulence, their ability to produce toxins, their antibiotic resistance and their technological performance in cheesemaking. The specific objectives of the Moorepark team were to study the co-metabolism of citrate and sugar by enterococci, develop a DNA probe to distinguish between Enterococcus and Lactococcus and evaluate the contribution of enterococci to flavour development in Cheddar cheese.