الفهرس 
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Abstract
Probiotics are known as microorganisms if taken in appropriate quantities that will have beneficial effects on the health of the host, is also one of the means currently used in disease prevention and treatment. Including bacteriosin, are natural antibiotics produced by most lactic acid bacteria and are characterized by their ability to eliminate some pathogenic bacteria and maintain the quality of the product added to it. Recent studies indicate that these bacteria can be used instead of preservatives to maintain the product for a long time without adding preservatives Industrial.Different brands of fermented milks were purchased from local supermarkets for measurement of different Lactobacillus bacteria as well as Bifidobacteria. Each sample representing a different production batch as determined by the different use by dates on the package. Each sample has a description of the bacteria which could be awaited according to direct or indirect labeling. In this study 300 samples of milk products were collected includingrayeb milk [100 samples (3 plants)], yoghurt [100 samples (3 plants)], cheese 100 sample including 4 types [Rass, Cheeder, Avanti and Emmental, 25 samples each].
Part I: Isolation and identification of probiotic bacteria from some dairy products:
Lactobacilli spp.in rayeb milk samples.It was found that their incidences in plant A, B and C was 39.1, 37and 14%, respectivly. It is evident that fromthe total 100 samples of rayeb milk, only 26% of samples were containedLactobacilli spp.
Different Lactobacilli spp.recovered from rayeb milk samplesfrom plant A asL.plantarum, L.brevis, L.casei, L.leichmanii, and L.fermentiin percentages of 13, 8.6, 4.3, 8.6, and 4.3% respectively. In plant B, L.plantarum, L.brevisandL.acidophiluswere isolated in incidences percentages of 7.4, 25.92, and 3.7%, respectively. While in case of plant C, L.plantarum,L.brevis andL.bulgaricus were found in percentages of 6, 6 and 2%, respectively. In all rayeb milk samplesL.plantarum, L.brevis, L.bulgaricus, L.casei, L.leichmanii, L.acidophilus and L.fermenti were detectedin percentages of 8, 12, 1, 1, 2, 1 and 1% of samples, respectively.
Bifidobacteria spp. in the examined rayeb milk samples were arranged descendingly as 39.1, 37 and14%of plant A, B and C, respectively. from allrayeb milk samples 26% of samples contained Bifidobacteria.
Bifidobacteria were isolated, in plant A B.dentium and B.subtilewere detected in percentages of 30.43 and 8.7, respectively. While,B.dentium, B.breve, B.subtile and B.animalisin plant B,were found in percentages of 22.22, 3.7, 3.7 and 7.4%, respectively. Furthermore, B.dentium, B.breve andB.subtilewere identified in incidences of10, 2 and 2% of tested samples in case of plant C, respectively. It is obvious that B.dentium, B.subtile, B.breveandB.animaliswere presented in percentages of 18, 4, 2 and 2%, respectivelyfrom all examined samples.
Lactobacilli spp.detected in yoghurt samples in a percentage of 31.6, 5 and 0% in plant A, B and C, respectively.
L.plantarum, L.brevis and L.fermentiwere found in percent of 1.66, 28.33 and 1.66 %respectively in plant A. While in plant B samples contained one isolate of L.plantaruminan incidence of 5%.
The percentage of Bifidobacteria spp.in the examined pasteurized yoghurt samples in plant A was 33.33%.While in plant B and plant C, 100% of samples were negative.
Incidence of Bifidobacterium spp. recovered from pasteurized yoghurt samplesin plant Awere identified as 5 species of Bifidobacteria, B.bifidum,B.dentium, B.breve, B.longumandB.animalis in apercentage of 1.66, 23.33,5, 1.66 and 1.66%, respectively.
High percentage of L.bacilliin the examined cheese samples were detected (Rass,Cheddar, Avanti, and Emmental), which was 100%.
Lactobacilli spp. recovered fromRasscheese samples were L.plantarum, L.brevis, L.bulgaricus, L.acidophilus and L.fermenti in 20, 16, 24,20 and 20% of samples, respectively. Also, these species were present in Cheddar cheesesamples inpercentages of 4, 20,40,24 and 12%, respectively. In case of Avanti cheese samples, the same isolates were recorded but in different percentages (4, 12, 24, 40 and 20%, respectively). Furthermore, Emmental cheese samples gave12, 8, 20 and 60%of L.plantarum, L.brevis,L.acidophilus and L.fermenti, respectively.
Bifidobacteria spp. were detected in 100% of cheese samples (Rass, Avanti, Cheddar and Emmental), 25 samples for each.
B.bifidum,B.dentium, andB.subtilewere detected in percentages of in percentages of 20, 20 and 60%, 8,20 and72%, 28, 28 and 44%, 12, 8 and 80% from Rass, Cheddar, Avanti and Emmental cheeses, respectively.
Part II: Antibacterial activity of isolated probiotic strains against L.monocytogenes.
Zones of inhibition were observed against Listeria monocytogenes in different diameters, they were 22, 30, 25 and 25 mm for L.plantarum, L.brevis ,L.bulgaricusandL.acidophillus, respectively.
Bifidobacteria strains were gave inhibition zones in diameters 30, 30, 26 and 24 for B.bifidum, B.dentium,B.subtileandB.animalisagainst Listeria monocytogenes.
Part III: Extraction and concentration of Bacteriocin from isolated probiotic bacteria:
Three methods were used for extraction and concentration of bacteriocin:
Pure bacteriocin extraction.
Ammonium sulphate extraction.
Absorption-desorption method.
Part IV: Antibacterial activity of extracted bacteriocin:
The results of the purification procedure from Lactobacillus strains against L.monocytogeneswereL.plantarum gave 22, 20 and 19mm,L.brevis gave 30, 20 and 19 mm, L.bulgaricus gave 25, 20 and 20 mm, L.acidophilusgave 25, 25 and 20 mm and L.fermenti gave 26, 18 and 20mm for pure bacteriocin,extraction with ammonium sulphate and absorption- desorption methods respectively. In contrary, L.casei and L.leichmaniiwhich gave negative results in all methods for purification.
Different diameters of inhibition zone against L. monocytogen by different bacteriocin extraction from Bifido bacteria isolates, B. bifidumgave 30, 26 and 23mm,B.denticumgave26, 20 and 22mm ,B.subtile gave 23, 10 and 15mm and B.animalisgave 24, 15 and 30 mm inhibition zone for pure bacteriocin,extraction with ammonium sulphate and absorption- desorption methods, respectively. In contrary, B.breve which gave negative results in all methods for purification.
The optimal bacteriocin anti-listerialeffects were achieved by pure bacteriocin extraction followed by ammonium sulphate precipitation and finalyabsorbition-desorbition method.
Part V: Estimation of the bacteriocin molecular weight using SDS-PAGE electrophoresis.
Molecular weight of bacteriocins producing by different strains of Lactic acid bacteria were 13.276, 13.69,13.586, 13.483, 13.276, 14.103, 13.172 and 14.621 KDa forL.plantarum, B.animalis, B.subtile, B. denticum, B.bifidum, L.brevis, L.acidophillus and L. bulgaricus,respectively.
Part VI: Comparison between effect of Lactobacilli spp. and bacteriocin extraction on S. aureus countduring and after preparation of yoghurt:
Addition of probiotic strains (L.fermenti and L.delbrukii) in a count of 1x1012 and their extracted bacteriocins to yoghurt supplemented by S.aureus 1x105 lead to reduction of count after curdling to 4.8 x 105, 2 x 105and 1x104cfu/g in yoghurt with S.aureus, yoghurt with S.aureus and probiotic and yoghurt with S.aureus and bacteriocins , respectively. After 72 hours, counts were 2.2x104and9x103 for yoghurt with S.aureus and yoghurt with S.aureus and probiotic. After 5 dayes count was10x102 in yoghurt with S.aureus only but it is not detected in yoghurt with probiotic or bacteriocins. Counts in yoghurt sample contained S.aureusdecreased till could not be detected at 8th day. After 10 dayes, Lactobacilli were isolated from a sample of yoghurt with probiotic bacteria on MRS agar but microorganism was not detected.Antibacterial activity assay of bacteriocin extraction was estimated in 13th day by well diffusion assay method which gave inhibitory zone 17 mm against S.aureuswith a count of 105cfu/g.While inhibition zone diameter of probiotic bacteria was 5mm.
Bacteriocins are biologically one of the important substances, and have been found to be useful in membrane studies and also in typing pathogenic microorganisms causing serious nosocomial infections.