Pasteurized milk in an unopened container spoils in the refrigerator. a sample reveals the presence of microorganisms. the most likely explanation is the microbes that survived pasteurization were able to grow at 4°c. pasteurization-resistant mutants developed after pasteurization the milk was pasteurized too long the pasteurization process was ineffective the microbes are pathogens

The microbes that survived pasteurization were able to grow at 4°C. Some microbes especially a class known as thermophiles are known to thrive in temperatures above 55 degrees Celsius. Chloroflexus aurantiacus, for instance, thrives in temperatures that ranges between 50 and 60 degrees Celsius. Thermus aquaticus thrives at an optimal temperature of 80 degrees Celsius. Milk, like any other diary product, is an excellent medium for microbial growth, and when stored at ambient temperature, other pathogens and bacteria would proliferate. Inactivation of the major milk-borne pathogens would require an above average temperature. Staphylococcus aureus at 66.5 °C and Yersinia enterocolitica at 62.5 °C, pathogenic Escherichia coli at 65 °C etc.