Evaluation of Antagonstic Effect of Lactic Acid Bacteria Isolated From Ergo Against Selected Foodborne Pathogens Inoculated in to Ayib
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Date
2011-10
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Addis Ababa University
Abstract
The antagonistic effects of mixed lactic acid bacteria cultures against foodborne pathogens
(Staphylocuccus aureus ATCC 25923, Shigella boydii clinical isolate, Pseudomonas aeruginosa
ATCC 25853) were evaluated on pasteurized ayib stored at room temperature. The lactic acid
bacteria were tested for acid tolerance at pH 2, 2.5 and 3 for three and six hrs, bile tolerance for
24 and 48 hrs at 0.3% (W/V) bile salt concentration and antimicrobial effect on selected
foodborne pathogens by co-culture assay in laboratory medium. Out of the 11 LAB isolates
tested for acid tolerance 6 isolates showed survivals at pH 2.5 and pH 3 for 3 hrs and most
isolates showed better tolerance to bile salt up on 24 and 48 hrs. Compared to the control
(without any LAB bacteria), Ps. aeruginosa were inhibited by all six isolates to varying degree
while, Sh. boyidii and S. aureus were inhibited by five of the isolates. Mixed LAB cultures of 106
cfu/g and test pathogens of 103 cfu/g were added together and separately in to ayib collected
from Shola market and pasteurized. The effects of LAB against the foodborne pathogens were
followed in ayib stored at ambient conditions for 9 days. The antagonistic effect of mixed LAB
reduced the pathogens population by more than 2 log units on average on the 6 day. Complete
elimination of the test organisms was achieved on day 5, 6, and 7 for Ps. aruginosa, S. aureus
and Sh. boyidii respectively. The result indicated the mixed LAB cultures eliminate the test
pathogen.
Key words: Ayib, Lactic acid bacteria, foodborne pathogens, antimicrobial effect
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Keywords
Ayib, Lactic acid bacteria, foodborne pathogens, antimicrobial effect