In comparative tests on 212 freshly isolated and reference cultures of gram-positive cocci, 85 showed anaerobic acid production from glucose in the currently recommended Hugh and Leifson test, but 138 showed anaerobic growth at the expense of glucose in a thioglycolate deep-tube test. Almost all of the discrepant results occurred in strains classified as micrococci of Baird-Parker's subgroups M1 through M4, but of the 106 strains of this type studied by us, only 55 showed anaerobic growth in the thioglycolate test. For practical purposes, the thioglycolate results therefore did not clarify the identification of strains in the M1 through M4 subgroups. Further experiments with modified forms of the pH change and growth detection tests showed that the results of the latter were susceptible to grossly different interpretations by different observers and that equally sensitive but more reliably interpretable results could be obtained with the pH change system.


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