The role of micro-organisms in dye-reduction and keeping-quality tests: II. The effect of micro-organisms when added to milk in pure and mixed culture

A study of the ability of pure cultures to reduce methylene blue and resazurin at 37·5° C., to reduce methylene blue at 22° C. and to cause milk spoilage as measured by precipitation with 68 % alcohol, and the clot-on-boiling test has revealed marked differences in behaviour between cultures. 2. At 37·5° C., with the exception of two cultures, there was good agreement between the time of reduction of methylene blue and resazurin. The two exceptions were a group BStreptococcuswhich reduced methylene blue but failed to reduce resazurin during the 9 hr. period of observation and an unclassifiedStreptococcusgrowing at 45° C. which reduced resazurin before methylene blue; the latter dye was found to retard the multiplication of the culture slightly.