Abstract
Bacteriocin-producing (Bac+) lactic acid bacteria (LAB) were isolated from a variety of food products and animal sources. Samples were enriched in de Man, Rogosa, and Sharpe (MRS) Lactocilli broth and plated onto MRS agar plates using a “sandwich overlay” technique. Inhibitory activity was detected by the “deferred antagonism” indicator overlay method using Listeria monocytogenes as the primary indicator organism. Antimicrobial activity against L. monocytogenes was detected by 41 isolates obtained from 23 of 170 food samples (14%) and 11 of 110 samples from animal sources (10%) tested. Isolated Bac+ LAB included Lactococcus lactis, Lactobacillus curvatus, Carnobacterium maltaromaticum, Leuconostoc mesenteroides, and Pediococcus acidilactici, as well as Enterococcus faecium, Enterococcus faecalis, Enterococcus hirae, and Enterococcus thailandicus. In addition to these, two Gram-negative bacteria were isolated (Serratia plymuthica, and Serratia ficaria) that demonstrated inhibitory activity against L. monocytogenes, Staphylococcus aureus, and Enterococcus faecalis (S. ficaria additionally showed activity against Salmonella Typhimurium). These data continue to demonstrate that despite more than a decade of antimicrobial interventions on meats and produce, a wide variety of food products still contain Bac+ microbiota that are likely eaten by consumers and may have application as natural food preservatives.
Highlights
Lactic acid bacteria (LAB) occur naturally on many retail foods and are often added as starter cultures in fermented products widely sold in the marketplace, such as cheese, yogurt, and buttermilk, while others are added as bacterial adjuncts, such as acidophilus milk or Bifidus yogurt [1,2]
We examined a variety of food and animal sources, screening for bacteriocin-producing lactic acid bacteria using Listeria monocytogenes as a primary indicator organism
Our objectives were to identify bacteriocinogenic lactic acid bacteria (LAB) indigenous to retail foods and animal sources that were inhibitory to L. monocytogenes
Summary
Lactic acid bacteria (LAB) occur naturally on many retail foods and are often added as starter cultures in fermented products widely sold in the marketplace, such as cheese, yogurt, and buttermilk, while others are added as bacterial adjuncts, such as acidophilus milk or Bifidus yogurt [1,2] Some of these organisms have gained notoriety for demonstrating a “probiotic” effect when ingested [3], while others are known for producing a variety of antimicrobials including lactic acid, hydrogen peroxide, bacteriophage, and bacteriocins which may be present in foods that are manufactured with them. Bacteriocins have varying inhibitory spectra and these properties allow for the development of applications towards roles in food safety or preventing spoilage [4,6] They can be used in tandem with other antimicrobial treatments (i.e., the hurdle effect) in order to enhance the preservation of food [7]. The use of bacteriocins as natural antimicrobials may be one possible way to replace or enhance chemical preservatives [3,5]
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