Bacteria of the
Corynebacterium genus are commonly associated with indigenous microbiota in the conjunctival sac of healthy individuals. Consistent with one of our prior studies,
31 Corynebacterium was the most abundant genus in the conjunctival sac of healthy controls in the current study. The reduction of relative abundance of
Corynebacterium has also been observed in some infectious diseases of ocular surface. We previously demonstrated that the decreased abundance of
Corynebacterium was associated with fungal keratitis.
35 As the “resident microbiota” on the ocular surface,
Corynebacterium was indicated to protect hosts from microbial infections through enhancing the immunological response by eliciting γδT cells to secrete IL-17.
36 In combination with our results, it may be deduced that the decrease of relative abundance of
Corynebacterium can lead to the impaired ability to resistance to pathogenic organisms for hosts and may be a factor of the pathogenic bacterial proliferation in the conjunctival sac. In clinical practice, the alleviation of MGD is often observed with antibiotic therapies. Compared with lid hygiene alone, patients who receive lid hygiene combined with topical metronidazole usually achieve significant improvement in ocular surface scores.
37 After treatment with azithromycin in 26 patients, the positivity rate of
Coagulase-negative Staphylococci and
Corynebacterium xerosis isolated from eyelid margins was reported to be significantly decreased.
38 Azithromycin could help improve clinical signs and parameters, such as tear film break-up time, Schirmer test, and meibomian gland plugging, of patients with MGD.
39–41 In this study, we found conjunctival sac bacterial imbalances in patients with MGD. Overgrowth of
Staphylococcus and
Sphingomonas provided microbiological evidence for investigating the mechanisms of the efficacy of antibiotics in MGD.
Staphylococcus is the most commonly encountered parasitic bacterium on human skin. As an opportunistic pathogen, it has been recognized to be closely associated with the incidence of bacterial keratitis, conjunctivitis, and endophthalmitis after cataract surgery.
42–44 Sphingomonas is an aerobic with low pathogenicity. Consistent with a previous study of dry eye disease,
45 the abundance of
Sphingomonas was higher in the MGD groups than the controls in our series. An increased relative abundance of
Sphingomonas was also observed in the conjunctival sac of diabetic patients.
46 Moreover, several clinical cases of endophthalmitis caused by
Sphingomonas were reported.
47–50 Although the specific role that these bacteria play in MGD remains unclear, their proliferation in the conjunctival sac of patients with MGD requires more attention. Clinicians should attach importance to preoperative management to assure the reduction of pathogens on the ocular surface before any ocular surgical procedure for MGD.
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