40 random samples of market milk sold in Assiut City were collected for enumeration and isolation of psychrotrophs and thermoduric psychro trophs. 15% of laboratory pasteurized milk samples contained thermo duric psychrotrophs immediately after pasteurization, while 67.5% of the samples had thermoduric psychrotrophs after storage at 7°C for 7 days.
Incubation at 21°C for 25 h method was a very reliable and rapid method to enumerate psychrotrophs in raw and pasteurized milk.
Psychrotrophic bacteria are the cause of major problems to the dairy industry for many years and will continue to be a problem in the future.