What are the recognized species of the genus Listeria?

is an important food-borne pathogen that affects the elderly, pregnant women, neonates and immune-compromised persons. In the last decade, there has been an increase in identification of new species from diverse sources, but remains the main pathogenic species of the genus. In recent times, investigators have reported different numbers of species for the genus; hence, it is important to clarify the number of species available now. A recent article [1] reported that the genus comprises up to 21 species. The authors relied on the information in the List of Prokaryotic Names with Standing in Nomenclature at the ‘Bacterio.net’ website (http://www.bacterio.net/listeria.html) to conclude 21 species. A closer perusal of the information on this site shows that some species taxonomy details were revised many years ago. The most pathogenic, , was originally described in 1926, but assigned the name in 1940 [2]. Although 22 species are listed, 2 species, namely and , are shown to be synonyms. The species was transferred to a new genus and renamed in 1987 [3] and has since been confirmed by two recent emendations [4, 5]. It was later found that high-level similarities exist between Listeria grayi and L. murrayi when a re-evaluation was carried out by Rocourt et al. [6] using several methods that included DNA–DNA hybridization, multilocus enzyme electrophoresis and rRNA restriction fragment length polymorphism. Hence, both were merged to a single species, , as a matter of priority. The emended strain can be obtained using the designation ATCC 25401 [7]. The 2oth species described is by Leclercq et al. [8] and they acknowledged 19 species existed before they described the new species. This is the last entry made in the International Journal of Systematic and Evolutionary Microbiology, the leading forum for the publication of novel microbial taxa and the International Committee on Systematics of Prokaryotes (ICSP) official journal record for prokaryotic names. The 20 species reviewed (Table 1) are the most up to date count of the number of species and not 21.

Table 1.

The species of the genus

No.	Species	Year	Reference
1	L. thailandensis	2019	[8]
2	L. costaricensis	2018	[9]
3	L. goaensis	2018	[10]
4	L. newyorkensis	2015	[11]
5	L. booriae	2015	[11]
6	L. riparia	2014	[12]
7	L. grandensis	2014	[12]
8	L. floridensis	2014	[12]
9	L. cornellensis	2014	[12]
10	L. aquatica	2014	[12]
11	L. weihenstephanensis	2013	[13]
12	L. fleischmannii	2013	[14]
13	L. rocourtiae	2010	[15]
14	L. marthii	2010	[16]
15	L. grayi	1992	[6]
16	L. ivanovii	1984	[17]
17	L. welshimeri	1983	[18]
18	L. seeligeri	1983	[18]
19	L. innocua	1983	[19]
20	L. monocytogenes	1940	[2]