الفهرس 
MATERIAL AND I\IETIIODSOnly 14 pages are availabe for public view
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Abstract
posure to heating, freezing, preservatives or disinfectants,
leaves some of surviving bacterial cells damaged. These in jured cells are still
viable, though their recovery by normal enumeration procedures is negatively affected.
Thus, bacterial popul:- tions nwy be seriously underestimated when a selective
medium is used for enumeration or specific bioimlicalors,
causing error and consequently health hazmd.
The aim of the present work is to study the cfTcct of some stressed environmental conditions on
the death and in jury of two universal bioindicalors: Hschcrichia coli and En lcmcoccus faccalis,
and recovery of the injured cells by dif ferent methods.
Liquid cultures of the tested organisms were subjected to several stress conditions including
healing (at 60 C for 4-10 min), freezing (-20, -40, -78C for I hr), high concentrations of sugar (I
0-60%) or salt (5-15%), sodium benzoate, sodium ni trite (0.02-0. I%), acetic acid, 1:- ctic acid
(0.25- 1.0%), hypo chlorite (2-1 0 ppm chlorine). Data revealed that the lethality percentages of
both tested organisms were directly propor tional to treatment intensity, meanwhile injured
cells were in duced in most treatments and their rates were not correspond ing with stress
intensity. Consequently convenient method should be used for repairing such injmcd rclls to grow
on the selective media.
EfTcct of exposing E. coli and EntemcoccusJirecalis to sublethal stress on some metabolic
properties was also stud ied. It wns found that stress conditions led to dccrc:1se the ac
tivities of dehydrogenase and dissimilatory nitrate reductase enzymes in both tested
organisms. rurthcrmore, the reactions of !MVIC tests were found to be slower in the stressed E.
coli cells than in the nornwl ones. The type of cellular damage was determined to be to protein
synthesis, RNA or cell wall by using specific antibiotics such as chloramphenicol, actinomy
cin [) and penicillin. The plasma membrane leakage was de termined by measuring the 260 & 280
11111 absorbing materials.
EfTccl of processing steps of carbonated beverage pro duction on the bioindicators was examined,
as a model of food processing Results exhibited very high rate of lethality, mean time a ratio of
injured cells was recorded in all treatments.
DifTcrcnt nutritional combinations were tried as recov ery suspending media to repair the injured
cells to find out the best one. t\ simple method for recovery was suggested. It was performed by
applying membrane-filler technique with are covery suspending medium consisting of pyruvate,
glucose and phosphate for 3 hr at 25 C; then adding trypticasc soy-yeast dcsoxycholatc broth for
counting E. coli or adding KF broth for counting Enterococcus faecalis.