Microbiota in MGD

Abstract

AbstractMGD is characterized by significant changes in meibum quality that may lead to the changes in the existing ocular surface flora that can contribute to the inflammatory state typical of the condition. Several papers have addressed this aspect. Li and coworkers, dividing the DE group into MGD and non‐MGD patients, found that no statistically significant differences between the two groups. 67 Pseudomonas, Bacillus, Acinetobacter and Corynebacterium were the most represented, although Bacilli showed a higher relative abundance in the MGD group and could be considered typical pathogens of MGD. Watters and colleagues studied patients with several degrees of MGD, among which CL wearers were included. Meibum expression did not modify the bacterial profile. CoNS were the most prevalent organisms isolated, present in two thirds of the population studied, although their presence was not correlated to the severity of MGD. CL wearers showed an increased presence of P. acnes that was correlated to MGD severity. No differences in microbiota were observed related to the severity of anterior blepharitis or CL wear. Dong and coworkers, using 16 S rDNA sequencing, investigated the microbiome of 47 Chinese MGD patients compared with a control group of 42 sex‐ and age‐matched subjects without MGD. They found significant differences at the phyla level, with a significantly higher abundance of Firmicutes (31.7% vs. 19.7%) and Proteobacteria (27.5% vs. 14.7%), and a lower abundance of Actinobacteria (34.2% vs. 57%) in MGD vs control patients. At the genus level, the numbers of Staphylococcus (20.7% vs. 7.9%) and Sphingomonas (5.7% vs. 0.8%) were significantly higher in patients with MGD vs controls, while the numbers of Corynebacterium (20.2% vs. 46.4%) were significantly lower. The meiboscores showed a significant direct correlation with the abundance of Staphylococcus in MGD patients. They concluded that patients with MGD can have bacterial microbiota alterations in the conjunctival sac, with a potential role of Staphylococcus, Corynebacterium and Sphingomonas sp. in MGD pathophysiology. In a previous study carried out on a small group of patients with blepharitis, Lee and coworkers demonstrated that blepharitis might be associated with a change in microbial composition, namely, greater quantities of Streptophyta, Corynebacterium and Enhydrobacter species. It was suggested that cytotoxicity and inflammatory components, triggered by bacterial growth, may contribute to the pathological process of MGD. Zheng et al confirmed the changes of ocular surface flora in MGD patients showing a wide bacterial profile and positive aerobic and anaerobic culture, significantly higher in both meibomian secretion and conjunctiva of MGD patients than in controls. The ocular surface inflammatory condition occurring in MGD and blepharitis could be mediated by the induced expression of acidic mammalian chitinase (AMCase) that is considered an immune response activator and is over expressed in MGD. It can be hypothesized that changes in ocular surface microbial flora can mediate AMCase upregulation.