Normal Flora of the Eye and Ear Microbiota (Microbiome)

Table of Contents

• List of Normal Flora of the Ear
• List of Norma Flora of the Eye
• Gram +ve and Gram -ve Bacteria of Eye and Ear
• Staphylococcus spp.
• Streptococcus spp. 
• Corynebacterium spp.
• Microbacterium spp.
• Bacillus spp. 
• Arthrobacter spp.
• Turicella otitidis
• Micrococcus spp.
• Pseudomonas spp.
• Moraxella spp.
• Haemophilus spp.
• Neisseria spp.
• Fungal Microbiota of Eye and Ear
• Aspergillus spp.
• Candida spp.
• Penicillium spp. 

The microorganisms known as "normal floras" are those that dwell unharmed on a healthy person's skin or mucous membrane. Bacteria and fungi that colonise the skin or mucous membrane for a little time or for the rest of their lives do not affect the host are considered to be part of the normal flora.

Because the conjunctiva, the outside layer of the eye, is immediately exposed to the outside world, it has a variety of bacterial flora. However, the natural flora in the eyes is relatively scarce because to the continuous cleansing activity of tears and the suppressive effect of lysozyme. Similar to this, the ear canal and outer ear both contain several species of the typical microbial flora. The inner surfaces of the eyes and ears are typically devoid of any microbial flora.

List of Normal Flora of the Ear

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

The outer ear canal naturally contains Staphylococcus species as resident bacteria. The most frequent species found in the ear canal are S. epidermidis and S. auricularis. Other prevalent Staphylococci in the ear canal include S. aureus, S. capitis, S. caprae, S. haemolyticus, S. hominis, S. pasteuri, and S. warneri.

The conjunctiva contains S. aureus, S. albus, S. epidermidis, and a few additional coagulase-negative Staphylococci.

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.

Humans' external auditory canals include Corynebacterium spp. such C. amycolatum, C. auris, C. falsenii, C. mucifaciens, C. tuberculostearicum, and others.

The conjunctiva also contains Corynebacterium spp. In healthy human conjunctiva, C. xerosis is the predominant corynebacterium.

Microbacterium spp.

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

The outer ear canal contains Microbacterium spp., including M. harmaniae subspecies B and C.

Bacillus spp. 

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

Bacillus species that are part of the typical microbiota in the outer ear canal include B. cereus, B. circulans, B. fusiformis, B. megaterium, B. simplex, B. pumilus, and B. choshinensis.

Arthrobacter spp.

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

Some people's ear canals are said to naturally harbour a few species of Arthrobacter.

Turicella otitidis

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

A typical commensal Corynebacterium found in human ear canals is T. otitidis.

Micrococcus spp.

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

In eyes, Micrococcus species are present as a passing flora. They are among the Gram-positive bacteria that predominate in human eyes.

In the ear canal, Micrococcus spp. are also present. The predominant species is M. luteus.

Pseudomonas spp.

• Gram-negative 
• Rod-shaped 
• Aerobic 
• Gammaproteobacteria 
• Family – Pseudomonadaceae
• Pseudomonas spp.

Few persons have reported having P. aeruginosa or P. stutzeri in their ear canal.

Moraxella spp.

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

Ear canals include M. catarrhalis and M. osloensis subspecies. The typical flora of human conjunctiva includes Moraxella spp.

Haemophilus spp.

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

In many people, Haemophilus spp. form part of the natural flora. In the human eye, they are the most common Gram-negative bacteria.

Neisseria spp.

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

According to reports, the human conjunctiva's natural flora includes N. catarrhalis and N. sicca.

Fungal Microbiota of Eye and Ear

Aspergillus spp.

A genus of filamentous fungus belonging to the Ascomycota order is called Aspergillus. Some persons have A. flavus, A. fumigatus, A. niger, and other species in their outer ear canals.

Candida spp.

A genus of yeast in the Saccharomycetaceae family is called Candida. The most often reported species are Candida albicans and Candida parapsilosis.

Penicillium spp. 

A genus of filamentous fungus belonging to the Ascomycota class is called Penicillium. The natural microflora of the human ear canal also includes Penicillium species such as P. chrysogenum, P. glabrum, P. viridicatum, and others.