Leptotrichia goodfellowii

Leptotrichia goodfellowii (also known as Pseudoleptotrichia goodfellowii) is a Gram-negative, non-spore-forming and non-motile anaerobic bacterium from the genus of Leptotrichia which has been isolated from human blood of an endocarditis patient. It is associated with infections in the oral cavity and respiratory tract. While primarily associated with opportunistic infections in immunocompromised individuals, its exact pathogenic mechanisms and clinical significance warrant further investigation.

Basic information
L. goodfellowii is an anaerobic, non-spore forming, gram-negative bacillus. It is typically found in blood, and when it was first found, it was plated on blood agar and incubated at 37 °C. It was gram-stained and analyzed via microscopy. It is rare, but when seen, it is a human pathogen typically in immunocompromised patients. It can cause endocarditis, which is inflammation of the heart chambers and valves, making it important to study, so we can learn how to best treat this condition. Leptotrichia spp are common in many human infections like bite wounds and bloodstream infections. Other phylogenies include Leptotrichia buccalis, hofstadii, hongkongensis, massiliensis, shahii, trevisanii, and wadei. Each of these neighbors can cause similar human infections, as they are all closely related.

Entymology
In 1683, Antonie Van Leeuwehhoek first discovered Leptotrichia, and the species L. goodfellowii was named in honor of Mike Goodfellow's significant contributions to microbial systematics.

Reclassification
After 16S rRNA gene sequence analysis, it was found that the six other strains of Leptotrichia were significantly more closely related than L. goodfellowii. This led Eisenberg et al. to propose reclassifying L. goodfellowii into its own genus, Pseudoleptotrichia. This proposal was validly published in 2020.

Taxonomy and phylogeny
Below are its taxonomic classifications and a partial phylogenetic tree of L. goodfellowii. The Leptotrichiaceae family consists of four genera, Streptobacillus, Sneathia, Sebaldella, and Leptotrichia. This entire family is fairly understudied, but research continues to be done about its genera. Streptobacillus have been implicated in causing disease, notably a type of rat-bite fever known as haverhill fever. Sneathia species have been found to have adverse pathogenic effects on the female reproductive system. Sebaldella has been isolated from insect intestinal tracts and its metabolic activity shows evidence of supplying organic nitrogen to its insect host.

Genomics
L. goodfellowii is hard to sequence by conventional methods, so molecular detection using 16S rDNA PCA followed by Sanger sequencing is most effective. The genome has been sequenced and is a mean total length of 2.28 Mb, with 2,199 genes, and 2,079 proteins. When conducting genomic analyses, the study conducted by Liebermann et al. worked with a species-level identification threshold of ~99.6%–99.7% similarity, and no significantly similar species were found; the next closest related species was canine oral Leptotrichia spp, which had similarity of 87.81%-89.57%.

Ecology
In regards to ecology, Leptotrichia can be found in bacterial biofilms, especially in the human oral cavity. L. goodfellowii has been found to colonize the human oropharynx and has also been isolated in human blood. Furthermore, L. goodfellowii has been isolated from a variety of sources, including oral swabs of guinea pigs, gastric fluid of patients who had stillborn child expulsion, and from the secretions of a healthy patient's dog bite wound.

Metabolism
L. goodfellowii are anaerobic chemoheterotrophic bacteria and are mesophilic, as they grow optimally at 37 °C. All Leptotrichia species ferment carbohydrates like glucose, maltitol, maltose, and lactose, and produce lactic acid as part of their metabolic pathways. A unique property of L. goodfellowii is that it can utilize sucrose isomers that other oral-bacteria like cannot. The DNA sequence of another Leptotrichia species, L. buccalis, contained the phosphoenolpyruvate:carbohydrate phosphotransferase (PEP-PTS) operon, which can be extrapolated to assume that L. goodfellowii would also include the PEP-PTS operon, as their metabolic activities are similar.

Pathology
L. goodfellowii must be detected molecularly, but is not always accurate due to poor or contaminated DNA quality. In one case study, a 66-year-old woman had culture-negative endocarditis. For her, 16S Sanger sequencing was not effective due to the above reasons. Researchers deconvoluted the sample using amplicon sequencing, which then allowed for appropriate pathologic diagnosis that her endocarditis was caused by L. goodfellowii. The best treatment for endocarditis caused by L. goodfellowii is β-lactam antibiotics. Most times, this disease has a fast onset and short but extreme course. In this case study, the patient did unfortunately pass away, however.