Microbiology of the Eye

Staphylococcus, Corynebacterium, and Propionibacterium are the most common bacteria found on eyelids and conjunctiva.

The cornea and anterior chamber (AC) are typically sterile, meaning they should not contain any microorganisms.

Gram-negative bacteria are less common on eyelids and conjunctiva compared to gram-positive bacteria. They are usually transient, meaning they don't stay for long.

Bacterial colonization of the eye changes during childhood. The bacterial spectrum becomes adult-like within 5 days after birth.

Fungal colonization of the eye is less common than bacterial colonization. It can occur on eyelids and conjunctiva, but typically in a smaller percentage of cases.

Direct scraping of a corneal ulcer is a common method to obtain a sample for bacterial culture and microscopic examination.

A corneal biopsy is a more invasive method of obtaining a sample for diagnosis of corneal infections, often used in severe cases.

The agar sandwich technique is used to isolate and culture bacteria from contact lenses. The lens is placed on a nutrient agar plate and bacteria are released into the agar.

Gram-positive bacteria stain blue, gram-negative stain red. Gram staining is essential for bacterial identification.

This technique uses dyes to highlight acid-fast bacteria, which are resistant to acid decolourisation. Mycobacteria are a classic example.

These dyes, like rhodamine and fluorescein, are used under a fluorescent microscope to visualize bacteria, fungi, and viruses.

This technique uses antibodies to identify the presence of Acanthamoeba, a type of amoeba that can cause infections.

These organisms, including Staphylococci, can grow in both the presence and absence of oxygen.

These organisms thrive in low oxygen environments, but require some oxygen to survive.

These organisms can only live in the absence of oxygen.

These organisms prefer cold temperatures, often below 15 degrees Celsius.

A type of culture medium used to grow different types of bacteria. It contains essential nutrients like carbohydrates, amino acids, salts, and agar, which acts as a stabilizing agent.

This type of culture medium is highly versatile and commonly used in medical laboratories. It contains all the necessary nutrients and 7% horse/sheep blood, making it suitable for the growth of a wide range of bacteria.

This agar medium is specifically used to isolate Neisseria and haemophilus bacteria. It is prepared by heating blood agar to 60 degrees for 10 minutes.

This type of medium is used to cultivate fungi, especially in the laboratory setting.

A liquid culture medium used to grow small quantities of organisms. It can also dilute the presence of any residual antibiotics in the sample (like eye samples).

A process of bacterial growth characterized by rapid multiplication. Bacteria divide quickly during this phase.

A common bacterial infection of the eyelids that can either be acute or chronic. Often caused by Staphylococcus aureus.

The most common bacteria responsible for blepharitis, can also cause lid abscesses.

Gram-positive cocci often found on the skin, playing a significant role in blepharitis.

The process by which bacterial cells divide into two identical daughter cells, a key mechanism of bacterial growth.

Gram-positive cocci commonly found on skin. They can cause styes and wound infections.

Gram-positive cocci known to cause severe lid infections and fasciitis.

Gram-negative rod that can cause a severe mucopurulent bacterial conjunctivitis.

A type of conjunctivitis characterized by a thick, pus-filled discharge.

A type of bacterial conjunctivitis where a membrane forms on the conjunctiva that bleeds when removed.

A condition where the cornea becomes infected by bacteria, viruses, fungi, or parasites.

The most common cause of MK in the UK, responsible for over 50% of cases.

An infection of the cornea characterized by severe scarring and often caused by Fusarium.

A type of yeast infection that can cause MK, particularly in immunocompromised individuals.

A free-living amoeba found in water that can cause serious MK.

A type of antibiotic used to treat bacterial infections that are resistant to other antibiotics.

A type of bacteria that is resistant to many antibiotics, often found in hospitals.

The ability of an organism to change its shape depending on the environment.

A gram-negative diplococci that can cause severe mucopurulent conjunctivitis and corneal involvement, especially in neonates.

A type of gram-negative rod that can cause serious MK, particularly in immunocompromised patients.

A small, clear, oval-shaped protozoan which can cause serious eye infections. Acanthamoeba is generally found in water and soil.

Inflammation of the junction between the cornea and sclera, often caused by Staphylococcus aureus.

A chronic condition where the small tubes that drain tears from the eye (canaliculi) become blocked. This can lead to excessive tearing, inflammation and anaerobic conditions.

A serious eye infection affecting the inside of the eye, most often due to surgery, trauma, or external infections.

A type of endophthalmitis that can show up weeks after a cataract operation. It happens when bacteria from the skin stick to the artificial lens implant and cause infection.

A medication that effectively targets a wide range of microorganisms. It's often used initially to treat eye infections before identifying the specific bacteria causing the infection.

A method of testing antibiotic sensitivity of bacteria. A disk containing an antibiotic is placed on an agar plate with bacteria. The zone of inhibition (no bacteria growth) around the disk indicates susceptibility.

A medication effective only against certain types of bacteria. It's used once the specific bacteria causing the infection has been identified.

Antibiotics that stop bacterial growth, but don't directly kill the bacteria.

Antibiotics that both inhibit bacterial growth and directly kill bacteria.

Medications used to reduce inflammation in the eye. They are often used in treating microbial keratitis to prevent scarring and preserve vision.

Treatment of microbial keratitis often involves intense therapy with antibacterial medications, typically in the form of eye drops.

The use of a single drug to treat an infection. It's often used for standard bacterial cases of keratitis

The use of multiple drugs to treat an infection. It's often used in cases of severe keratitis or when the cause of the infection is unclear.

A method of treating severe corneal ulcers with stronger antibiotics, like aminoglycosides and cephalosporins.