The recovered results showed that: the incidence of Salmonella typhymurium in the observed commercial egg-layer flocks; the isolation of Salmonella typhymurium from 5 flocks (33.7 %) out of 15 flocks, the mortalities rates at the end of 78 weeks of age was 16 % and also, the current egg-production, average egg weight, hen housed day, hen housed egg and percent peak of egg-production were: 68 %,59.2 gm, 68.4%, 318, 78% and 70%, respectively. The efficacy of the most common disinfectants against Salmonella typhymurium was determined. The selected disinfectants were; Formalin, Phenol, QAC, Halamid, Virkon'S and Micro Sept M against Salmonella typhymurium isolates of the studied commercial egg- layers in Egypt (hfq gene of Salmonella typhimurium). It was observed that, S. typhimurium affected significantly only by Micro Sept M and Virkon'S, at low rate of application; the Log 10 of populations after15 mint exposure were 4.2, 4.4, respectively the recovered results showed also, that: Formalin, Phenol, Micro Sept M and Virkon'S treatment demonstrated a significant reduction in Salmonella typhymurium populations at high rate of application. It is evident from the results using formalin, phenols and QAC at concentration of 4% ,5% and 33.3 % by fogging other than spraying had increased action on the tested pathogens S. typhimurium after 15 min contact time (35.7%,42.8 % and 76.8%, respectively).
