![]() Subsequent studies utilizing approaches to sequence prokaryotic 16S ribosomal RNA genes (16S rRNA) for identification of ocular bacterial communities confirmed the presence of Staphylococcus and Pseudomonas spp., amongst others, and further developed our understanding of the ocular microbiome beyond those species detectable by in vitro culture. The authors found several microbial species, including Staphylococcus spp., Pseudomonas spp., other Gram-negative populations and fungal species ( Capriotti et al., 2009). Efforts to define the normal ocular flora in African populations were initially conducted in rural Sierra Leone. The ocular surface is still generally considered to harbor a paucibacillary community, although bacteria have been isolated from higher proportions of healthy conjunctivae by using more intensive modern culture techniques ( Perkins et al., 1975). Initial reports generally considered between 20 and 80% of normal healthy eyes to be sterile. Thus far there have been a limited number of studies that have investigated the interaction between the non-chlamydial ocular microbiota and conjunctival immune response in trachoma ( Burton et al., 2010 Hu et al., 2012).Ĭulture-dependent methods have been used extensively to study the ocular surface microbiome, the first descriptions dating back to 1930 ( Keilty, 1930). In addition to Ct infection, other factors, including the type and quality of the conjunctival host immune responses ( Holland et al., 2010 Natividad et al., 2010 Burton et al., 2011b Ramadhani et al., 2017), host genetic background ( Roberts et al., 2014b), infections with other ocular pathogens and changes in overall bacterial community composition ( Burton et al., 2011a Hu et al., 2011a, 2018 Zhou et al., 2014) have each been linked to the different stages of trachomatous disease. The factors involved in the inflammatory responses to repeated Ct infection that lead to conjunctival scarring, trichiasis, corneal opacity and blindness remain poorly understood. The pathophysiology of trachoma is complex and multifactorial ( Hu et al., 2013 Ramadhani et al., 2016a). Ocular Chlamydia trachomatis ( Ct) infection causes trachoma, the leading infectious cause of blindness worldwide. Comparisons between active and scarring trachoma supported the relative absence of type-2 interferon responses in scarring, whilst highlighting a common suppression of re-epithelialization with altered epithelial and bacterial adhesion, likely contributing to development of scarring pathology. In scarring trachoma, expansion of non-pathogenic bacteria such as Corynebacterium and innate responses are coincident, warranting further investigation of this relationship. Interpretation: In the absence of current Chlamydia trachomatis infection, changes in the ocular microbiome associate with differential expression of antimicrobial and inflammatory genes that impair epithelial cell health. Increased abundance of Corynebacterium in scarring disease was associated with innate immune responses to the microbiota, dominated by altered mucin expression and increased matrix adhesion. Adults with scarring trachoma had a reduced ocular bacterial diversity compared to controls, with increased relative abundance of Corynebacterium. Haemophilus enrichment was associated with antimicrobial responses but not linked to active trachoma. We recruited children with active trachoma and adults with conjunctival scarring, alongside corresponding matched controls.įindings: In children, active trachoma was not associated with significant changes in the ocular microbiome. Methods: Ocular swabs from trachoma endemic populations in The Gambia were selected from archived samples for 16S sequencing and host conjunctival gene expression. Host responses to ocular chlamydial infection resulting in chronic inflammation and expansion of non-chlamydial bacteria are hypothesized risk factors for development of active trachoma and conjunctival scarring. 2Disease Control and Elimination Theme, MRC Unit the Gambia at LSHTM, Banjul, Gambiaīackground: Trachoma, a neglected tropical disease, is the leading infectious cause of blindness and visual impairment worldwide. ![]() 1Clinical Research Department, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom.Palmer 1 †, Joanna Houghton 1 †, Pateh Makalo 2, Hassan Joof 2, Tamsyn Derrick 1, Adriana Goncalves 1, David C.
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