Antimicrobial Activity of Lactococcus and Lactobacillus Species Isolated from Raw Goat Milk. San Luis Argentina
Abstract
The goat milk and their products are used to human consumption with health benefits. The lactic acid bacteria (LAB) have ability to produce bacteriocins that inhibit the growth of spoilage microorganisms or pathogens present in food. In this study, bacteriocins-producing strains were isolated from goat milk samples. The isolates were able to inhibit the growth of Listeria monocytogenes ATCC 74902, Enterococcus faecalis ATCC 29212, Escherichia coli and/or Pseudomonas aeruginosa strains with an average inhibition halo between 8 and 12 mm. The strains were identified as Lactococcus lactis ssp lactis 2 (gmSL3, gmSL9, gmSL11, gmSL12, gmSL15 and gmSL40), Lactobacillus fermentum (gmSL28), Lactobacillus paracasei ssp paracasei 1 (gmSL5, gmSL20 and gmSL23). The antimicrobial substances showed high stability at temperatures and/or pH extremes. The tested strains inhibit the growth of more than one pathogen, of both bacteria Gram (+) and Gram (-). By RT-PCR, one band of 136 bp was found, whose size corresponds to Nisin A.
Keywords
Download Options
Introduction
Goat milk and cheese are foods that offer certain advantages over the cow milk and derivatives; the higher content of short chain fatty acids and small globules of fat promotes the digestion. In addition the goat milk contains more calcium, phosphorous and potassium as that human milk and cow milk. Furthermore, the high content of retinol and alpha-tocoferol, the goat’s milk can replace milk cow in people with allergy to the protein present in the last one [1- 3]. Goat's milk and its derivatives are usually present in the diet of the population in different regions of the Argentine Republic. In the State of San Luis several dairy farms distribute their products to regions away from the production site, they should be consumed in a short period of time to avoid the loss of its nutritional values, so it is necessary to find new methods of conservation to prolong the useful life of these foods.
It has also been observed contamination of raw milk and the process of maturation of the cheese with spoilage microorganisms or pathogens such as Listeria monocytogenes, E.coli and other members of the family Enterobacteriaceae [4, 5]. These microorganisms can cause changes in the taste of food or diseases that affect the health of the consumer.
It is important to have safe methods for the preservation of food to prevent food poisoning that can cause damage to the health of the population. In the last ten years studies in this field have multiplied, aimed at reducing the use of chemical preservatives and at developing new conservation techniques employing physical methods and/or use of natural antimicrobials synthesized by bacteria present in various foods such as milk, fermented products and processed foods. [4-12]
Lactic Acid Bacteria have been used as fermentation starters in food and beverage industries because they contribute to taste and flavor development, and to prevent food spoilage. LAB’s protective role is attributed to their capacity to decrease pH, and to synthesize bacteriostatic and bactericidal substances. These substances include hydrogen peroxide, lactic acid, carbon dioxide and bacteriocins, or other similar compounds. LAB have been isolated from different sources such as meat, meat products, cow dairy products, fish, etc. Recently, many research studies are aimed at finding new strains of bacteriocinproducing LAB that could be used in foods preservation processes. Most studies on this topic have used cow milk and its derivatives as a LAB source; however, goat milk has been less studied. Studies by Guesas and Kihal [9] on LAB isolates of raw goat milk indicate that the predominant bacteria are: Lactococcus sp, Streptococcus thermophilus, Leuconostoc sp. and Lactobacilli.
Conclusion
According to the results presented above, we can conclude that raw goat milk obtained from a dairy located in the Province of San Luis (Argentina) has bacteriocin-producing LAB strains in its microbiota, which can inhibit the growth of food pathogens and spoiling organisms, L. monocytogenes and/or E. faecalis and/or E. coli and/or P. aeruginosa. The fact that the first two pathogens are Gram(+) strains, and that the latter are Gram(-) broadens the action spectrum of these bacteriocins. Some strains can inhibit more than one pathogen, which makes them interesting to focus in future studies. Todorov S.D and Dicks isolated lactobacillus bacteriocin-producer, stable a pH values between 2.0 and 10,0 and at 100ºC active against Gramnegative bacteria [20]. Our results are similar in most of the bacteriocins produced by the isolated, activity at low pH and temperature extremes, some of them are active at alkaline pH, allowing its use in different environmental conditions. These results lead us to continue our studies in search of new LAB strains with broad-spectrum inhibitory against disruptive or pathogenic microorganisms in food. The tests performed at the molecular level showed a band of bp 136 that matches the pattern of band of nisin in one of the five strains studied. Therefore, these strains can be useful to produce this particular bacteriocin, which is the only one authorized for the Food and Agriculture Organization of the United Nations (FAO) to add to food [21]. Given the interest that exists in the use of these peptides in food preservation or to control pathogens human, it would be interesting to purify and identify these and other bacteriocins in future studies.