The basic taxonomic group in bacteria, yeasts, and molds is the species, and each species is given a name. The name has two parts (binomial name): the ﬁrst part is the genus name and the second part is the speciﬁc epithet (adjective). Both parts are Latinized; when written, they are italicized (or underlined), with the ﬁrst letter of the genus written in a capital letter (e.g., Saccharomyces cerevisiae, Penicillium roquefortii, and Lactobacillus acidophilus). A bacterial species can be divided into several subspecies (subsp. or ssp.) if the members show minor but consistent differences in characteristics. Under such conditions, a trinomial epithet (subspeciﬁc epithet) is used (e.g., Lactococcus lactis ssp. lactis or Lactococcus lactis ssp. cremoris). In some instances, ranks below subspecies are used to differentiate strains recognized by speciﬁc characters (e.g., serovar, antigenic reaction; biovar, producing a speciﬁc metabolite; and phagovar, sensitive to a speciﬁc phage). Such ranks have no taxonomic importance but can be practically useful (e.g., Lactococcus lactis ssp. lactis biovar diacetilactis is a Lactococcus lactis ssp. lactis strain that produces diacetyl, an important ﬂavor compound in some fermented dairy products). Each strain of a species should be identiﬁed with a speciﬁc strain number, which can be alphabetic or numeric or a mixture of both (e.g., Pediococcus acidilactici LB923). At the family level, bacterial names are used as plural adjectives in feminine gender and agree with the sufﬁx “aceae” (e.g., Enterobacteriaceae). The species and strains in a genus can be represented collectively, either using “spp.” after genus (e.g., Lactobacillus spp.) or plural forms of the genus (e.g., lactobacilli for Lactobacillus; lactococci for Lactococcus; leuconostocs for Leuconostoc, or salmonellae for Salmonella).
The scientiﬁc names of bacteria are given according to the speciﬁcations of the International Code of Nomenclature of Bacteria. The International Committee on Sys- tematic Bacteriology of the International Union of Microbiological Association exam- ines the validity of each name and then publishes the approved lists of bacterial names from time to time. A new name (species or genus) must be published in the International Journal of Systematic Bacteriology before it is judged for inclusion in the approved list. Any change in name (genus or species) has to be approved by this committee.
When writing the name of the same species more than once in an article, it is customary to use both genus and speciﬁc epithet the ﬁrst time and abbreviate the genus name subsequently. In the Bergey's Manual of Systematic Bacteriology, only the ﬁrst letter is used (e.g., Listeria monocytogenes and then L. monocytogenes). The same system is used in most publications in the U.S. However, it creates
confusion when one article has several species with the same ﬁrst letter in the genus (e.g., Lactobacillus lactis, Leuconostoc lactis, and Lactococcus lactis as L. lactis). In some European journals, more than one letter is used, but there is no deﬁnite system (e.g., Lact. lactis, Lc. lactis, Leu. lactis, Lb. lactis, List. monocytogenes). In this book, to reduce confusion among readers, many of whom might not be familiar with the current rapid changes in bacterial nomenclature, a three-letter system is used (e.g., Lis. monocytogenes, Leu. lactis; Sal. typhimurium for Salmonella; Shi. dysenterie for Shigella; Sta. aureus for Staphylococcus). In rare cases, a slight modiﬁcation is used (e.g., Lactococcus lactis and Lactobacillus lactis are written as Lac. lactis and Lab. lactis, respectively, for the two genera). Recently, the nomen- clature system for Salmonella has been modiﬁed.
The viruses, as indicated previously, have not been given speciﬁc taxonomic names as given for bacteria. They are often identiﬁed with alphabetic or numeric designation, or a combination of both (e.g., T4 or l bacteriophages), the disease they produce (e.g., hepatitis A, causing liver inﬂammation), or by other methods (e.g., Norwalk-like viruses, causing a type of foodborne gastroenteritis in humans).