Eye and Ear Microbiota (Microbiome)- Normal Flora of Eye & Ear

Normal floras are the microorganisms that live on the body surface or mucous membrane of a healthy individual without causing any infection. Normal flora includes bacteria and fungi that colonize the skin or mucous membrane for short period or throughout life without harming the host.

Normal Flora of Eyes and Ears
Normal Flora of Eyes and Ears

The outer layer of the eye (or conjunctiva) is directly exposed to the outer environment and hence contains different bacterial flora. However, due to the constant washing action of tears and inhibitory action of lysozyme, normal floras in the eyes are very sparse. Similarly, the outer ear and ear canal also contain different species of normal microbial flora. Inner parts of both the ears and the eyes are normally free of any microbial flora. 

List of Normal Flora of the Ear

Gram-Positive BacteriaGram-Negative BacteriaFungi
Staphylococcus spp.
Corynebacterium spp.
Microbacterium spp.
Bacillus spp. 
Arthrobacter spp.
Turicella otitidis
Micrococcus spp.
Alloiococcus otitis
Pseudomonas spp.
Moraxella spp.
Aspergillus spp.
Candida spp.
Penicillium spp.

List of Norma Flora of the Eye

Gram-Positive BacteriaGram-Negative Bacteria
Staphylococcus spp.
Streptococcus spp.
Corynebacterium spp.
Haemophilus spp.
Neisseria spp.
Moraxella spp. 

Gram +ve and Gram -ve Bacteria of Eye and Ear

Staphylococcus spp.

  • Gram-positive
  • Catalase-positive 
  • Coagulase positive and coagulase-negative
  • Aerobic
  • Cocci bacteria 
  • Family – Staphylococcaceae
  • Known for producing grape-like clusters under a microscope 

Staphylococcus species are normally present in the outer ear canal as resident flora.  S. epidermidis and S. auricularis are the most common species in the ear canal. S. aureus, S. capitis, S. caprae, S. haemolyticus, S. hominis, S. pasteuri, and S. warneri are other common Staphylococci in the ear canal. 

S. aureus, S. albus, S. epidermidis, and a few other coagulase-negative Staphylococci are present in the conjunctiva.  

Streptococcus spp. 

  • Gram-positive
  • Anaerobic and facultative anaerobic 
  • Catalase-negative 
  • Cocci bacteria arranged in the chain under a microscope
  • Family – Streptococcaceae 

Non-hemolytic streptococci are present in the conjunctiva. 

Corynebacterium spp.

  • Gram-positive 
  • Rod-shaped (club-shaped), 
  • Aerobic bacteria 
  • Family –  Corynebacteriaceae
  • The characteristic features of high mesodiaminopimelic acid and highly repeated arabinogalactan

C. amycolatum, C. auris, C. falsenii, C. mucifaciens, C. tuberculostearicum, and other Corynebacterium spp. are found in the external auditory canal of humans.

Corynebacterium spp. are also found in the conjunctiva. C. xerosis is dominant Corynebacteria in healthy human conjunctiva.  

Microbacterium spp.

  • Gram-positive
  • Rod-shaped
  • Non-sporing
  • Family – Microbacteriaceae

M. harmaniae subsp. B and subsp. C and other Microbacterium spp. are found in the outer ear canal. 

Bacillus spp. 

  • Gram-positive
  • Rod-shaped
  • Motile
  • Obligate aerobic and some facultative anaerobic
  • Spore forming
  • Family – Bacillaceae

B. cereus, B. circulans, B. fusiformis, B. megaterium, B. simplex, B. pumilus, B. choshinensis are Bacillus spp. residing in the outer ear canal as normal microbiota.  

Arthrobacter spp.

  • Gram-positive
  • Rod as well as cocci (pleomorphic)
  • Strictly aerobic
  • Family – Micrococcaceae
  • A characteristic feature of snapping type cell division

A few species of Arthrobacter are reported as a normal inhabitant of the ear canal in a few people. 

Turicella otitidis

  • Gram-positive
  • Pleomorphic
  • Non-sporing
  • Non-fermentative
  • Catalase-positive
  • Family – Corynebacteriaceae

T. otitidis is a common commensal Corynebacteria found in the ear canal of people. 

Micrococcus spp.

  • Gram-positive 
  • Mostly non-motile (few species are motile) 
  • Strictly aerobic 
  • Cocci in clusters 
  • Family – Micrococcaceae

Micrococcus spp. are found in eyes as transient flora. They are one of the dominant Gram-positive bacteria in the human eyes.

Micrococcus spp. are also found in the ear canal. M. luteus is the dominant species. 

Pseudomonas spp.

  • Gram-negative 
  • Rod-shaped 
  • Aerobic 
  • Gammaproteobacteria 
  • Family – Pseudomonadaceae

P. aeruginosa and P. stutzeri are reported in the ear canal of few people. 

Moraxella spp.

  • Gram-negative
  • Rod-shaped or coccobacilli (M. catarrhalis are diplococci)
  • Oxidase and catalase positive
  • Aerobic
  • Gammaproteobacteria 
  • Family – Moraxellaceae

M. catarrhalis, M. osloensis subspecies are found in ear canals. Moraxella spp. are also normal flora of human conjunctiva.  

Haemophilus spp.

  • Gram-negative 
  • Coccobacilli (pleomorphic) 
  • Aerobic or facultative anaerobic 
  • Gammaproteobacteria 
  • Family –  Pasteurellaceae

Haemophilus spp. are found as normal flora in many individuals. They are predominant Gram-negative bacteria in the human eyes.

Neisseria spp.

  • Gram-negative 
  • Aerobic or facultative anaerobic 
  • Cocci (and diplococci) 
  • Betaproteobacteria 
  • Family –  Neisseriaceae 

N. catarrhalis and N. sicca are reported as normal flora of the human conjunctiva.  

Fungal Microbiota of Eye and Ear

Aspergillus spp.

Aspergillus is a genus of filamentous fungi in the division Ascomycota. A. flavus, A. fumigatus, A. niger, and other species are found in the outer ear canal of some people. 

Candida spp.

Candida is a genus of yeast in Saccharomycetaceae family. C. parapsilosis and C. albicans are the most frequently reported species. 

Penicillium spp. 

Penicillium is a genus of filamentous fungi in the division Ascomycota.  P. chrysogenum, P. glabrum, P. viridicatum, and other Penicillium species are also normal microflora of the human ear canal.

References

  1. Subadh Chandra Parija. Textbook of Microbiology and Immunology. 2nd edition. Elsevier, a division of Reed Elsevier India Private Limited. ISBN: 978-81-312-2810-4.
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  9. Sthapit, Purnima. (2014). Conjunctival Flora of Normal Human Eye. JSM Ophthalmology. 2. 1021.
  10. CASON, L., & WINKLER, C. H., Jr (1954). Bacteriology of the eye. I. Normal flora. A.M.A. archives of ophthalmology, 51(2), 196–198. https://doi.org/10.1001/archopht.1954.00920040198005
  11. Regis P. Kowalski, Melvin I. Roat, Paul P. Thompson. Normal Flora of the Human Conjunctiva and Eyelid. Normal Flora of the Human Conjunctiva and Eyelid | Ento Key
  12. Turicella otitidis – Microregistrar.com
  13. Sthapit PR, Tuladhar NR, (2014) Conjunctival Flora of Normal Human Eye. JSM Ophthalmol 2(2): 1021.

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