A. Definitions

The term infrasubspecific subdivision (or division) has been used in two ways to denote both terms and taxa. It is preferable to distinguish them as given below. Infrasubspecific "subdivision" has been used rather than "division" to avoid any confusion with the taxonomic category "division" (divisio).

Note. Infrasubspecific subdivisions are not arranged in any order of rank, and may overlap one another.

1. Infrasubspecific taxa. An infrasubspecific taxon is one strain or a set of strains showing the same or similar properties, and treated as a taxonomic group.
   Example: Staphylococcus aureus phagovar 81.
   The sets of properties used may be of a similar kind but are not necessarily the same.
   Example: The susceptibility to a different phage may be used to define another phagovar of Staphylococcus aureus, e.g., phagovar 42D.
   Infrasubspecific taxa based on different sets of properties may overlap; e.g., one serovar may contain strains belonging to different phagovars.
   Example: Salmonella typhi serovars, phagovars, and biovars.
2. Infrasubspecific terms. An infrasubspecific term is used to refer to the kinds of taxa below subspecies.
   Examples: serovar, chemovar, forma specialis.
   If a species has not been divided into subspecies, the infrasubspecific terms may be applied to other subdivisions within that species. The subdivisions so named would still be infrasubspecific subdivisions for nomenclatural purposes until such time as they may be raised to subspecific or specific rank.
   Example: Serovars of Erysipelothrix rhusiopathiae.
3. Use of other terms. Infrasubspecific form has been used to refer to a bacterial strain, but this use should be avoided.
   A culture of bacteria is a population of bacterial cells in a given place at a given time, e.g., in this test tube or on that agar plate. It may have a longer duration, e.g., desiccated cultures.
   A clone is a population of bacterial cells derived from a single parent cell.
   A strain is made up of the descendants of a single isolation in pure culture. A strain is usually made up of a succession of cultures and is often derived from a single colony. The number of bacteria which gave rise to the original colony is often unknown. Most bacterial strains are not known to be clones.
   Individual is a term with little meaning in bacteriology and has been applied to a single bacterial cell or to a bacterial strain; therefore, it is best to avoid the use of this term.

B. Infrasubspecific Terms

Table 5 contains some of the terms which are commonly used, and the preferred name appears in the first column. The introduction of the suffix "-var" or "-form" to replace "-type" is recommended to avoid confusion with the strict use of the term "type" to mean nomenclatural type (see Rule 15).

Table 5

Infrasubspecific terms.

The term "type" in bacteriology should be used strictly for a nomenclatural type (Principle 5 and Chapter 3, Section 4). It should not be used to designate a division of a species nor to designate taxa based on antigenic characters.

The term "group" is informal and has no nomenclatural standing. It may prove useful to designate informally a set of organisms having certain characteristics in common, provided that it is used with care and exact definition to avoid ambiguity. It should not be used to avoid the use of the correct name of a taxon such as genus or species.

However, it may be useful when the bacteriologist does not wish to give a formal name to a set of bacteria until further studies have been made but wishes to publish his results and seek the opinion of others.

Example: "IID group," later named Cardiobacterium hominis.

C. Nomenclature of Infrasubspecific Taxa

An infrasubspecific taxon is designated or cited by the name of the species followed by the infrasubspecific term used to designate this infrasubspecific subdivision followed by the infrasubspecific designation.

Example: Staphylococcus aureus phagovar 81.

Reference strains of infrasubspecific taxa may be designated.

There are many ways that infrasubspecific taxa may be designated; among these are the following: latinized words, e.g., cerealis in Xanthomonas translucens f.sp. cerealis; vernacular names or words, e.g., rough phase; numbers, letters, or formulae, e.g., phagovar 42D in Staphyloccocus aureus phagovar 42D.

D. Nomenclature of Strains

A strain may be designated in any manner, e.g., by the name of an individual, by a locality, or by a number.