Theodorou, M. | bioRxiv Science

bioRxiv2022

Genomic evaluation of a case of Lacticaseibacillus rhamnosus endocarditis: comparison with commercial yogurt isolates and examination of global population structure

Probiotics, including yogurt commonly containing bacteria of the Lactobacillus group, are widely used to promote microbiome health and to prevent gastrointestinal or other infections, especially in the setting of antibiotic use. Rarely, however, Lactobacillus bacteria have caused invasive or severe infections in patients. In this report, we present a patient with fatal Lacticaseibacillus bacteremia and endocarditis who frequently consumed yogurt. Whole genome sequencing identified the patients bloodstream isolate as Lacticaseibacillus (formerly Lactobacillus) rhamnosus, and sequencing of Lactobacillus isolates from selected commercial yogurt preparations revealed one isolate nearly identical to the patients isolate, differing by only one nucleotide (adenine to guanine substitution leading to a M1A amino acid change in the start codon of the nrdR gene). To place these sequences into broader context of L. rhamnosus strains, we compared them to 602 L. rhamnosus genome sequences publicly available through the National Center for Biotechnology Information repository. Both isolates belonged to a clade, identified in this report as clade YC, composed of mostly gastrointestinal isolates from healthy individuals, some of which also differed by only a single nucleotide from the patients isolate. Members of clade YC had only rarely been previously identified in invasive infections. In summary, the Lacticaseibacillus strain causing this patients infection may have originated from a commercial dairy product or from the commensal flora of his gastrointestinal tract. This study demonstrates that whole genome sequencing may be insufficient to reliably determine the source of invasive infections caused by L. rhamnosus. IMPORTANCEActive culture and probiotic foods and supplements are often used to promote gut health. Though largely considered safe for human consumption, there are rare reports of severe infections linked to bacterial species used in these products. Using whole genome sequencing, we examined a case of fatal infection with Lacticaseibacillus rhamnosus in the patients blood. By comparing the bacterial genome sequence from the patient to strains cultured from 4 commercial yogurt samples and 602 publicly available sequences of L. rhamnosus from around the world, we found that it was nearly identical to one of the yogurt strains and equally similar to other strains from both probiotics and healthy individuals gastrointestinal tracts. These findings show that even with whole genome sequencing it can be difficult to determine the source of an invasive L. rhamnosus infection, whether from recent consumption of a probiotic or dairy product versus from the gastrointestinal microbiome.

microbiology↗

bioRxiv2021

Eye movements elevate crowding in congenital idiopathic nystagmus

Idiopathic infantile nystagmus syndrome is a disorder characterised by involuntary eye movements, which leads to decreased acuity and visual function. One such function is visual crowding; a process whereby objects that are easily recognised in isolation become impaired by nearby flankers. Crowding typically occurs in the peripheral visual field, though elevations in foveal vision have been reported in congenital nystagmus, similar to those found with amblyopia. Here we examine whether the elevated foveal crowding with nystagmus is driven by similar mechanisms to those documented in amblyopia - long-term neural changes associated with a sensory deficit - or by the momentary displacement of the stimulus through nystagmus eye movements. We used a Landolt-C orientation identification task to measure threshold gap sizes with and without either horizontally or vertically placed pairs of flanking Landolt-Cs. Because nystagmus is predominantly horizontal, crowding should be stronger with horizontal flankers if eye movements cause the interference, whereas a sensory deficit would more likely be equivalent for the two dimensions. Consistent with an origin in eye movements, we observe elevations in nystagmic crowding that are above that of typical vision, and stronger with horizontal than vertical flankers and not found in amblyopic or typical vision. We further demonstrate the same pattern of performance can be obtained in typical vision with stimulus movement that simulates nystagmus. Consequently, we propose that the origin of nystagmic crowding lies in the eye movements, either through image smear of the target and flanker elements or through relocation of the stimulus into peripheral retina.

neuroscience↗