Commensal ocular bacteria degrade mucins

Antimicrobial activity in tears prevents infection while maintaining a commensal bacterial population. The relation between mucin and commensal bacteria was assessed to determine whether commensals possess mucinolytic activity, how degradation depends on mucin integrity, and whether mucins affect bacterial replication.

Bacteria were sampled from healthy eyes and contact lenses from asymptomatic wearers. Intracellular mucins were extracted and purified from cadaver conjunctivas, and surface mucins from extended wear contact lenses. After exposure to bacteria, changes in mucin hydrodynamic volume (proteolytic cleavage) and subunit charge (oligosaccharide degradation) were assayed by size exclusion and ion exchange chromatography. The effect of mucin on bacterial replication was followed for up to 24 hours from the end of incubation with purified ocular mucins.

Ocular bacteria decreased the hydrodynamic volume of intracellular and contact lens adherent mucins, irrespective of glycosylation density. A decrease in mucin sialylation was observed after exposure to commensal bacteria. Subunit charge distributions were generally shifted to lesser negative charge, consistent with loss of charged epitopes. Subunits with high negative charge, observed after digesting lightly adhering contact lens mucins with bacteria, suggest preferential cleavage sites in the mucin molecule. The presence of purified ocular mucin in the medium inhibited bacterial growth.

Bacteria in the healthy ocular surface possess mucinolytic activity on both intact and surface processed mucins, targeted to discrete sites in the mucin molecule. Inhibition of bacterial growth by ocular mucins can be seen as part of the mucosal control of microbiota.