Comparison of three culture methods for the differentiation of Micrococcus and Staphylococcus in fermented squid shiokara

Abstract

The accuracy in the differentiation between Micrococcus and Staphylococcus with three culture methods has been evaluated, using bacterial strains isolated from ika-shiokara, a traditional Japanese fermented squid meat. A total of 530 strains of Gram-positive, catalase-positive cocci isolated from ika-shiokara as well as the type strains of Micrococcus (eight strains) and Staphylococcus (26 strains) was differentiated with three culture methods using furazolidone-peptone (FP) agar, Schleifer-Krämer (SK) agar, and oxidation-fermentation (OF) test of glucose. All the type strains of both genera used were clearly differentiated on FP agar, and well differentiated on SK agar with some exceptions, while only 46% of Staphylococcus could be identified correctly on the OF test. Among the 530 strains of Gram-positive, catalase-positive coccal isolates, 491 strains were identified as Staphylococcus on the FP & SK agar, while only 73 strains were identified as Staphylococcus on the OF test. To obtain detailed accuracy, 55 strains were randomly selected from the 530 strains and were further examined by DNA base composition (mol GC%) assay. The results on the FP & SK agar revealed 100% similarity with the results obtained by mol GC% assay, while the OF test of glucose revealed only 24% similarity with them. These results confirmed that OF test of glucose such as Baird-Parker's method is misleading method, which is still of relatively common use for differentiation of these two genera in food microbiological study. The simultaneous use of FP & SK agar was suggested to be useful in routine identification system in food microbiological study.