Elsevier

Experimental Eye Research

Volume 117, December 2013, Pages 99-105
Experimental Eye Research

Review
Characterization of the normal microbiota of the ocular surface

https://doi.org/10.1016/j.exer.2013.06.003Get rights and content

Highlights

  • It is unknown whether the ocular surface contains a normal microbiota.

  • Culture of the conjunctiva yields small numbers of bacteria but not on all occasions.

  • Molecular techniques may establish whether the ocular surface has a unique microbiota.

Abstract

The ocular surface is continually exposed to the environment and as a consequence to different types of microbes, but whether there is a normal microbiota of the ocular surface remains unresolved. Using traditional microbial culture techniques has shown that <80% of swabs of the conjunctiva yield cultivable microbes. These usually belong to the bacterial types of the coagulase-negative staphylococci, Propionibacterium sp., with low frequency of isolation of bacteria such as Staphylococcus aureus, Micrococcus sp., Gram-negative bacteria or fungi. Even when these are grown, the numbers of colony forming units (cfu) per swab of the conjunctiva is usually much less than 100 cfu. Swabs of the lid more commonly result in microbial growth, of the same species as from the conjunctiva and slightly higher cfu. Contact lenses have also been cultured, and they yield similar microbial types. Microbes can be isolated from the ocular surface almost immediately after birth. The advent of molecular techniques for microbial identification based on 16S rRNA sequencing has opened up the possibility of determining whether there are non-cultivable microbes that can colonise the ocular surface. Additionally, use of these techniques with cross-sectional and longitudinal studies may help to understand whether the ocular surface harbours its own unique microbiota, or whether the microbiota are only transiently present.

Section snippets

Cultivable microbiota of the conjunctiva, lids and tears

The ocular surface is continually exposed to the environment and as a consequence to different types of microbes. This can occur during birth and at any time throughout life. Many studies have examined the types of microbes that can be routinely cultured from swabs of different parts of the ocular surface. Tables 1 and 2 show composite data from many of these studies for the conjunctiva, lids and tears (Campos et al., 1994, Capriotti et al., 2009, de Caro et al., 2008, Elander et al., 1992,

Cultivable microbiota of contact lenses during wear

Attempts have been made to culture all of the microbes adherent to contact lenses. Contact lenses can be composed of many different types of polymers (for example poly(methyl methacrylate) (PMMA), (hydroxyethyl)methacrylate (HEMA), or the so-called silicone hydrogel materials), and can be worn on either daily disposable, daily wear or extended wear bases, and studies have examined a wide range of materials and wear schedules for numbers of cultivable microbes (Table 4) (Baleriola-Lucas et al.,

Effect of contact lens wear on the cultivable microbiota of the conjunctiva and lids

Several studies have examined the effect of contact lens wear on the microbes that can be cultured from the conjunctiva or lids. Stapleton et al. (1995) found that long term extended wear of HEMA-based lenses did not alter the conjunctival or lid microbiota, but extended wearers were more commonly colonised on these two surfaces by potential pathogenic microbes (such as Gram-negative bacilli). In contrast, daily wear of HEMA-based lenses was associated with an increase in colonisation frequency

Sources of the microbiota and effect of age on the microbiota of the eye

Examination of the cultivable microbiota of the conjunctiva immediately after birth has shown that it is composed of similar microbiota as the cervix, that is predominantly Haemophilus vaginalis, viridans streptococci, S. epidermidis, Micrococcus sp., Bacillus sp, diphtheroids, Bacteriodes sp., Propionibacterium acnes, Peptococcus sp., Peptostreptococcus sp., Gardnerella sp., Lactobacillus sp., Bifidobacteria sp., Escherichia coli, S. aureus, and Candida sp. (Brook et al., 1979, Eder et al.,

Comparison of cultivable ocular microbiota to that of other mucosal surfaces

The oral cavity harbours a very diverse microbiota. Whereas tears contain <100 cfu/μl, (Larkin and Leeming, 1991) saliva contains 107–108 cfu/μl (Evaldson et al., 1982). Swabs of the buccal mucosa yield confluent growth on non-selective agar plates 100% of times, and it has been estimated that there are between 0 and 25 cfu/buccal mucosal cell and 100 cfu/tongue mucosal cell (Theilade, 1990). The predominant microbial types that can be cultured from the oral cavity include streptococci,

The human microbiome project and the ocular microbiome

The preceding information has concentrated on the cultivable microbiome from the ocular surface as this has been most commonly studied. However, it is clear that the cultivable microbiome represents only a fraction of the microbes that can colonise the human. It has been known for many years that microbiologists are unable to culture all microbial types. For example, the bacterium Treponema pallidum that causes syphilis is not able to be grown on traditional laboratory media. With the discovery

Conclusion

The issue of whether there is a normal ocular surface microbiota is still unresolved. The beginning of the use of molecular techniques to probe the microbiome of the ocular surface holds promise, and initial evidence shows that there are potentially non-cultivable microbial types on the ocular surface. However, cross-sectional and longitudinal studies are needed to study the acquisition of this microbiota and changes that may occur leading to infection or inflammation. The diverse reports of

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