AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Microorganisms
Plurals

When referring to the common vernacular plural of a genus, use roman lowercase letters (Table 9.5-1). For organisms that do not have a common plural, add the word species or organisms to the genus name to indicate a plural use (see 14.14, Organisms and Pathogens).

Table 9.5-1. Plural Noun Forms for Microorganisms