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Abstract
Summary
Two hundred and forty random samples of raw, pasteurized, UHT, and flavored UHT milk (60 samples each) were collected from street vendors, shopkeepers, farms, and supermarkets in Assiut city.
Pseudomonas species could be detected on CN agar, in 33(55%), 25(41.66%), 18(30%) and 4(6.6%) of raw, pasteurized, UHT and flavored UHT milk samples, respectively. On the other hand, on CFC agar, Pseudomonas spp. could be detected in 32(53%), 27(45%), 17(28.3%) and 2(3.3%) of the examined milk samples.
The average counts of Pseudomonas spp. were 13.5x105, 3.1x104, 4.06x102 and 0.9x10/ml on CN agar, while on CFC agar, there were 13.8 x105, 3.45x104, 4.52x102 and 0.83x10 from raw, pasteurized, UHT, and flavored UHT milk.
Of 94 Pseudomonas isolates obtained from the examined milk samples on CN agar, 7 were Ps.aeruginosa, 6 Ps.alcaligenes, 30 Ps.cepacia, 5 Ps.diminuta, 28 Ps.fluorescens, 1 Ps.pickettii, 9 Ps.putida, 1 Ps.putrefaciens, 5 Ps.stutzeri and 2 Ps.vesicularis.
On the other hand, of 84 Pseudomonas isolates from the examined raw, pasteurized, UHT and flavored UHT milk on CFC agar, 13 were Ps.aeruginosa, 6 Ps.alcaligenes, 25 Ps.cepacia, 3 Ps.diminuta, 26 Ps.fluorescens, 6 Ps.putida, 4 Ps.stutzeri and 1 Ps.vesicularis, while, Ps.pickettii and Ps.putrefaciens couldn’t be detected by CFC agar.
By comparing the efficiency of the two media for the isolation of Pseudomonas spp., it was found that there is no significant difference between the results obtained using CN and CFC media.
The characterization of some Pseudomonas spp. isolated from the examined milk samples for the production of extracellular virulence factors as proteolytic and lipolytic enzymes, were studied. Out of 174 Pseudomonas spp., 126 possessed proteolytic activity and of these a high positive percentage (90%), (88.88%), (78.18%), (74.07%) and (71.42%)were Ps.aeruginosa, Ps.stutzeri, Ps.cepacia, Ps.fluorescens and Ps.diminuta respectively followed by Ps.putida (46.66%) and Ps.alcaligenes (41.66%). While, only 105 showed lipolytic activity, which assigned as follow 74.07% Ps.fluorescens, 65% Ps.aeruginosa, 62.5% Ps.diminuta, 56.36% Ps.cepacia, 55.55% Ps.stutzeri, 53.33% Ps.putida and 25% Ps.alcaligenes. On the other side, Ps.pickettii, Ps.putrefaciens and Ps.vesicularis couldn’t produce any enzymes.
The effect of honey on survival of Ps.aeruginosa was evaluated using different concentrations of honey (0.00, 5 and 10%) in yoghurt which was laboratory prepared, inoculated with the previously isolated and identified Ps.aeruginosa to yield a concentration of 33.7x108 cfu/g, Ps.aeruginosa counts and pH value were determined daily.
The sensitivity of Ps.aeruginosa to honey and pH was demonstrated by a reduced count on CN agar. Ps.aeruginosa couldn’t be detected after 2 days in the samples of yoghurt containing honey in concentrations 5 and 10%, while, on control samples Ps.aeruginosa failed to be detected after 4 days of storage at 4°C.
Additionally, effect of garlic (0, 1 and 5%) on the survival of Ps.aeruginosa in yoghurt stored at 4°C was estimated, where yoghurt were prepared and inoculated with the previously isolated and identified Ps.aeruginosa, the count and pH values were determined daily.
The results indicated that Ps.aeruginosa wasn’t able to survive with garlic, after 2 days of storage at 4°C. On the other hand, Ps.aeruginosa could be survived in yoghurt free from garlic till the 3rd day of storage at 4°C.
The public health significance of the organism and the precautions, which should be taken to control this organism in the dairy industry as well as the recommended sanitary measures, were also discussed.