الفهرس 
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Abstract
A key element of disinfection is the choice of a suitable disinfecting agent in appropriate concentration for sufficient contact time. The presented study aimed to investigate the bactericidal effectiveness of six commercial disinfectants against seven prevalent and common bacterial genera causing disease problems in aquatic ecosystem mostly were gram negative rods. The evaluation assays was conducted in two stages of experimental work; in vitro laboratory testing following Quantitative European suspension BS CEN 1276 test methods and requirements, followed by in vivo evaluation of bactericidal effectiveness of the tested disinfectants after acute and chronic toxicity testing following OECD (guideline no. 203) test method; for determination of Median Lethal concentration (LC50) and No Observed Effect Concentration (NOEC), beside investigation the safety application of the tested disinfectants into aquatic systems. With exception of Biosentry® Iodine™, nearly all tested disinfectants at 1.25 the recommended use dilution and after 5 min contact time achieved significant log reduction (P ˂ 0.05) and pass criteria of at least 5 against the majority of tested organisms, except Vibrio alginolyticus that was noticed to be resistant to most tested disinfectants. The in vivo work revealed that efficient bactericidal effectiveness was achieved by Virkon-S®, Aldekol des- Gda® and Peraclean® at NOEC against three selected strains, Aeromonas hydrophila (gyr-B LC012344), Pseudomonas aeruginosa and V. alginolyticus at ID50 inspite of their concentrations were lower than the LC50 values, on the other hand TH4® disinfectant failed to achieve the bactericidal effect against the 3 inoculated strains at their ID50, inspite of its efficient bactericidal reduction efficacy under in vitro conditions. Therefore, we concluded that Virkon-S®, Aldekol des- Gda® and Peraclean® are of wide safety margin and can be used for the control of infections might cause by A. hydrophila, Ps. aeruginosa and V. alginolyticus in vivo achieving efficient bactericidal effectiveness in contrary to TH4 that failed to achieve in vivo bactericidal effectiveness due to possible biological breakdown. The standardized steps for testing disinfectants in Laboratory tests and in vivo work mimic Field trial (in loco tests) is recommended to be followed to achieve complete evaluation data about the tested disinfectants for more verification.