University of Khartoum

Antagonistic Activity of Lactic Acid Bacteria, Isolated from Dairy Products, Against Food-borne Pathogens (Escherichia coli and Staphylococcus aureus)

Antagonistic Activity of Lactic Acid Bacteria, Isolated from Dairy Products, Against Food-borne Pathogens (Escherichia coli and Staphylococcus aureus)

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Title: Antagonistic Activity of Lactic Acid Bacteria, Isolated from Dairy Products, Against Food-borne Pathogens (Escherichia coli and Staphylococcus aureus)
Author: Eissa, Maha Mohamed
Abstract: The aim of this study was to investigate the effect of antimicrobial activity of bacteriocin producing lactic acid bacteria isolated from dairy product samples, against foodborne pathogen, Escherichia coli and Staphylococcus aureus. A total of 40 lactic acid bacteria (LAB) isolated from cow milk (W), camel milk (C) and cheese (H) were identified. Phenotypic tests confirmed that all isolates were homofermentative lactic acid bacteria. Of these, 52% were identified as enterococci, 30% as lactobacilli and 18% of the strains were identified as pediococci. All LAB isolates were screened for antagonistic activity, using an agar-spot test under conditions that eliminated effects of organic acids and H₂O₂. Seventy percent of isolates produced inhibitory substances primarily active against the indicator organisms, S. aureus and E. coli. The cell-free supernatants of 15 isolates, showing positive antagonistic activity against foodborne pathogens, were tested for sensitivity to the proteolytic enzyme pepsin. Thirteen supernatants 87% were inactivated after treatment with pepsin. This proteinaceous nature and antimicrobial mode of action indicated that the inhibitory substance is a bacteriocin. With the aim of evaluating the suitability of using bacteriocin-producing LAB as biopreservatives, the effect of foodborne pathogens on the growth of the LAB isolates was tested. The isolates W14 and C7 were selected, based on gram staining, biochemical properties and agar spot test, and co-cultured with S .aureus and E. coli in separate batches, and their growth was monitored in MRS broth over 36 hrs. This was compared to a control batch where W14 and C7 were cultured without the foodborne pathogens. The growth of bacteriocin-producers in co-cultured batches was not affected by foodborne pathogens (S. aureus and E. coli). To examine the effect of bacteriocin producing LAB on the growth of foodborne pathogens as potential biopreservative agents, selected LAB (W14 and C7) were co-cultured with E. coli (W14+ E),(C7+E), and S. aureus (W14+S),( C7+S), over a period of 36 hrs. Growth of E. coli, and S. aureus was monitored on McConkey agar and Violet Red Bile Dextrose agar, respectively every 6 hrs. The E. coli counts in batch W14+E decreased from 8.5 to 3.8 log CFU/ml and from 8.5 to 3.4 log CFU/ml in C7+E over the 36 hrs. However S. aureus was more sensitive to both bacteriocin - producing LAB (W14 and C7) as compared to E. coli and it was decreased from 4 log CFU/ml undetectable levels in both batches (W14+S and C7+S). To study the influence of the bacteriocin – producers on the growth of foodborne pathogens in-situ, sour milk batch (SC) was prepared using a mixture of starter cultures (W5, W7, C4, W14, C7 and H7) and a control batch (C) was left to ferment spontaneously. The presence of E. coli and S .aureus was monitored at 0h and after 24 hrs fermentation. E. coli counts were approximately 3.86 and 3.53 log CFU/ml at 0 time in control batch and starter-culture batch, respectively. S. aureus counts were approximately 5.63 and 5.54 log CFU/ml at same time in batch C and inoculated SC, respectively. After 24 hrs fermentation, control batch C showed a decrease in E. coli to 3.27 log CFU/ ml and S. aureus by 4.58 log CFU/ml. No growth of E. coli or S. aureus was detected after 24 hrs in SC batch. Bacteriocin-producing LAB isolated from dairy products showed good potential for application as biopreservatives in controlling foodborne pathogens.
Description: 79 Pages
URI: http://khartoumspace.uofk.edu/123456789/23272


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