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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. |