Proper Names

Q. In CMOS (chapter 8), I have read that one should italicize the genus name of an organism even without its species name written. Like the example in paragraph 8.120: “The Pleistocene saber-toothed cats all belonged to the genus Smilodon.” I am a BS biology major and have been taught not to italicize the genus name if it doesn’t have a species name with it or an sp. for unspecified species. Since the current guide the company I am in uses CMOS, do I have to write/type every genus name in italicized form? I am currently copyediting a book for grade 7 teachers and I have seen genus names such as Micrococcus, Diplococcus, Staphylococcus, Streptococcus, Bacillus, Proteus, Spirillum, Thiospillum, and Vibrio.

A. In Chicago style (see paragraph 8.127), when a genus name is used in the vernacular (perhaps as in your schoolbook), you may lowercase it in roman type: the streptococcus and bacillus bacteria. If you are referring to the genus as a genus (as in 8.120), use italics and an initial cap, whether or not it stands alone.