Weissella is a genus earlier considered a member of the family Leuconostocaceae, which was reclassified into the family Lactobacillaceae in 1993. There have been studies emphasizing the probiotic and anti-inflammatory potential of various species of Weissella, of which W. confusa and W. cibaria are the most representative. Other species within this genus include: W. paramesenteroides, W. viridescens, W. halotolerans, W. minor, W. kandleri, W. soli, W. ghanensis, W. hellenica, W. thailandensis, W. fabalis, W. cryptocerci, W. koreensis, W. beninensis, W. fabaria, W. oryzae, W. ceti, W. uvarum, W. bombi, W. sagaensis, W. kimchi, W. muntiaci, W. jogaejeotgali, W. coleopterorum, W. hanii, W. salipiscis, and W. diestrammenae.
1. Introduction
The Weissella genus has begun to take center stage in the past few years owing to its probiotic potential and its many prospective applications, ranging from the healthcare industry to the skin care and food industries. Due to its ability to thrive in stomach acid and bile, adherence to intestinal cells, and its antimicrobial potential against other pathogenic microorganisms including but not limited to Staphylococcus aureus, Listeria monocytogenes, Salmonella typhi, and Salmonella enterica, most Weissella species meet the pre-requisites needed to be classified as a probiotic. The only limitation to its widespread use is the lack of a significant volume of research at the moment and a handful of reported cases of pathogenicity. However, a bulk of these cases are a result of some preexisting disposition or comorbidity associated with the host. Despite such pathogenic potential, researchers set to investigate to what extent this genus is clinically treatable with common antimicrobials in the event of its identification in human infections. Herein, researchers primarily describe the antimicrobial and anti-inflammatory potential of Weissella and summarize the commonly used antibiotics in clinical settings where humans were diagnosed and treated/cured of Weissella infections.
The
Weissella genus was first considered a member of the family
Leuconostocaceae due to their significant shared similarities
[1] but later on differentiated into a distinguished genus, which was named ‘
Weissella’ after the German microbiologist Norbert Weiss
[2]. It was reclassified based on the phenotypic and genotypic analysis by Collins in 1993
[3]. The bacteria in this genus are non-spore-forming, generally non-motile, Gram-positive and catalase-negative
[4] in nature that exist as either rods or ovoid-shaped cocci
[5] belonging to the phylum
Firmicutes and the family
Lactobacillaceae. These bacteria are found to thrive in various ecological environments such as soil
[6], plants, freshwater lakes
[7], spontaneously fermented vegetables, and animal foods
[8][9]. They can also be present as commensals on the skin surface and in the saliva and gastrointestinal tract of humans and animals as regular residents. The gastrointestinal tract is particularly thought to be a reservoir for colonization by
Weissella [10].
2. Taxonomy and Sources of Isolation
According to the taxonomy database at The National Center for Biotechnology Information (NCBI, txid46255), as of October 2022,
Weissella consists of 22 species:
Weissella bombi, Weissella ceti,
Weissella cibaria, Weissella coleopterorum, Weissella confusa, Weissella diestrammenae,
Weissella halotolerans,
Weissella hanii,
Weissella hellenica,
Weissella jogaejeotgali,
Weissella kandleri,
Weissella koreensis,
Weissella minor,
Weissella muntiaci,
Weissella oryzae,
Weissella paramesenteroides,
Weissella sagaensis,
Weissella salipiscis,
Weissella soli,
Weissella thailandensis,
Weissella uvarum, and
Weissella viridescens. However, Teixeira et al.
[11] (February 2021) reported that 25 species of
Weissella have been validated, whereas Fanelli et al.
[12] grouped 26 species of
Weissella into 6 phylogenetic clusters. Outside of the NCBI database, six more species are found in the ‘List of Prokaryotic names with Standing in Nomenclature’ database (
https://lpsn.dsmz.de/genus/weissella) accessed on 18 October 2022:
Weissella beninensis, Weissella cryptocerci, Weissella fabalis, Weissella fabaria, Weissella ghanensis, and
Weissella kimchi. Twenty-six of these species are validly published under the International Code of Nomenclature (ICNP), except for
Weissella salipiscis. It is to be noted that when taking into consideration the NCBI and LPSN databases together, 28 species of
Weissella have been reported (
Table 1).
Of the known species of
Weissella, two
(W. confusa and
W. cibaria) have been reported from human or animal clinical infections
[13]. However, the metagenome analysis of human fecal samples obtained from IBD patients and controls in the laboratory revealed the presence of several
Weissella species (Singh et al. unpublished data). All known species of
Weissella and their varied sources of isolation include: meat (
W. viridescens, W. halotolerans, W. minor), fermented animal and plant-based food items (
W. confusa, W. jogaejeotgali, W. kimchi, W. hellenica, W. thailandensis, W. koreensis, W. ghanensis, W. sagaensis, W. beninensis, W. fabaria, W. fabalis, W. oryzae, W. hanii, and
W. salipiscis), animal/insect sources (
W. ceti,
W. diestrammenae,
W. cryptocerci,
W. bombi,
W. muntiaci, and
W. coleopterorum), wine/wine grapes (
W. paramesenteroides and
W. uvarum), soil (
W. soli and
W. kandleri), and human samples (
W. cibaria).
Table 1. Summary of sources of most common Weissella species.
As published in the BV-BRC (Bacterial and Viral Bioinformatics Resource Center) database, as of 19 October 2022, the genome for the genus Weissella (Taxonomy Id: 46255) has been reported a total of 448 times, of which the genome for Weissella cibaria has been reported the most (n = 168), followed by Weissella confusa (n = 128) and Weissella paramesentroides (n = 44). The sources of isolation being: human (n = 95), insect (n = 20), avian (n = 9), nonhuman mammal (n = 21), plants, and fermented food sources. The genomes of five species have been reported as isolated from humans: Weissella cibaria, Weissella paramesenteroides, Weissella koreensis, and Weissella confusa. With respect to the genome size, Weissella has a smaller pool of genes compared to other fecal commensal bacteria belonging to the genera Parabacteroides, Bacteroides, Lactobacillus, and Pediococcus. As investigated in the laboratory (Singh et al., unpublished), the genome size and the coding sequence (CDS) of the Weissella genus are much smaller than the other fecal bacteria.
3. Safety and Virulence Genes
The safety of
W. confusa has always been a controversial subject due to reports of its isolation from human clinical samples. Although not formally assigned to a risk group by the American Biological Safety Association (ABSA), it has been allocated to Risk Group 1 microorganisms by the German Committee for Biological Agents. The American Type Culture Collection (ATCC) recommends using the strain ATCC 10881
TM under biosafety level 1
[7], which makes it unlikely to cause disease in healthy individuals.
Some potential virulence determinants, such as hemolysin, collagen, and adhesin, have been discovered in some of the species of the genus
Weissella through genome analysis
[6], but their role and transferable potential across
Weissella are still unknown. As in other lactic acid bacteria (LAB), hemolysin genes are universally present in the genus, but their role in pathogenicity remains unproven. The presence of some adhesins may be a desired characteristic in favor of the probiotic potential of
Weissella. For example, a fibronectin-binding protein (
FbpA) present in
W. cibaria strains inhibits the biofilm formed by
S. aureus, thus being protective against
S. aureus infections. While there is some evidence to suggest the role of the gut-colonizing potential of
FbpA in establishing infection in a host, one cannot ignore that the ability for gut-colonization is essential to the probiotic potential of
Weissella, as demonstrated by Wang et al.
[39]. Similarly, mucus-binding proteins play a crucial role in the adhesion of probiotic bacteria to the host gut
[40].
It is important to establish the safety of bacteria designed for human consumption to ensure that the organisms are well tolerated and do not pose a health threat when properly administered. To evaluate the safety of these organisms, animal models are typically given higher doses than would be administered to a human. Lyophilized
W. confusa orally administered to rats at a concentration of 92 × 10
8 CFU/kg body weight/day for 90 days did not show any evidence of mental or physical ailment when evaluated using a combination of behavioral tests as well as physical examination. Blood cell counts did not show a significant difference in erythrocyte, white blood cell, or lymphocyte concentrations in untreated versus treated rats when controlling for sex
[41].