Microbiology of the Eye

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Questions and Answers

Which of the following is true regarding microbial presence in the eye?

Ocular samples rarely yield any microorganisms upon testing.

Gram-negative bacteria are commonly persistent colonizers in healthy eyes.

The conjunctiva typically harbors more microorganisms than the eyelids.

The cornea and anterior chamber are generally considered sterile. (correct)

Which of the following bacterial types is MOST frequently found in the eyelids and conjunctiva of healthy adults?

Gram-negative bacilli

Gram-positive, coagulase-negative Staphylococci (correct)

Coagulase-positive Staphylococci

Streptococcal species

Which of the following is NOT a commonly isolated bacterial isolate found in the lids and conjunctiva?

Micrococcus

Bacteriodes

Staphylococcus aureus

Streptococcus pneumoniae (correct)

At birth, the bacterial spectrum is different but becomes adult like within how many days?

5 days (D) Signup and view all the answers

Which of these is NOT a typical step in obtaining a corneal scraping for suspected microbial infection?

Applying preserved topical anesthetic prior to scraping. (B) Signup and view all the answers

Which method is employed for analyzing contact lenses suspected of harboring microorganisms?

Agar sandwich and lens maceration techniques (B) Signup and view all the answers

Which of the following is a method for investigating viral infections of the eye?

Direct examination of tissue scrapes (A) Signup and view all the answers

What is recommended following foreign body removal and patching in the eye?

Prophylactic antibiotics to prevent infection (B) Signup and view all the answers

Which of the following is NOT a common application of PCR testing?

Identifying acid-fast bacteria (B) Signup and view all the answers

During the Gram staining procedure, what is the primary function of acetone or alcohol?

To decolorize the slide, removing stain from Gram-negative bacteria (A) Signup and view all the answers

If a bacterial sample exhibits a blue color after a Gram stain, it is likely to be:

Gram-positive bacteria or yeast (A) Signup and view all the answers

Which staining method is MOST appropriate for identifying mycobacteria that resist decolorization by acid?

Ziehl-Neelsen stain (A) Signup and view all the answers

An organism that thrives in an atmosphere with reduced oxygen levels is described as:

Microaerophilic (B) Signup and view all the answers

What type of organism is MOST likely to grow well in both aerobic and anaerobic conditions?

Facultative (A) Signup and view all the answers

Which of the following best describes the purpose of the immuno-peroxidase staining technique?

Determining the presence of acanthamoeba. (B) Signup and view all the answers

At what temperature are most micro-organisms routinely cultured in a lab?

37 degrees Celsius (D) Signup and view all the answers

Which of the following is NOT a typical component of laboratory culture media for growing bacteria?

Fungal spores (B) Signup and view all the answers

What is the primary function of agar in bacterial culture media?

To act as a setting agent and provide a stable medium (C) Signup and view all the answers

Which type of culture medium is MOST suitable for isolating Neisseria and Haemophilus species?

Chocolate agar (B) Signup and view all the answers

Which of the following is NOT a stage in bacterial growth?

Inert phase (A) Signup and view all the answers

What is the primary purpose of using broth media in the context of eye samples?

To dilute any residual antibiotics present in the sample (C) Signup and view all the answers

Which type of agar is commonly used for the isolation of fungi?

Sabouraud's agar (C) Signup and view all the answers

What is the most common bacterial species responsible for clinical cases of blepharitis?

Staphylococcus aureus (A) Signup and view all the answers

Which of the following best describes the method used to collect specimens from the eyelid for blepharitis diagnosis?

Moistened swab of bacteriological nutrient broth applied to the lid (B) Signup and view all the answers

What is a key characteristic of coagulase-negative staphylococci?

They are major commensals of the skin. (D) Signup and view all the answers

Why do N. gonorrhoeae and N. meningitidis require an additional 5% carbon dioxide for optimal growth?

To mimic their natural environment within the human body (A) Signup and view all the answers

Which bacterial species is a common cause of styes on the eyelid?

Staphylococcus aureus (C) Signup and view all the answers

Which of the following is a gram-negative diplo bacilli that can cause severe microbial keratitis?

Moraxella species (D) Signup and view all the answers

Which bacterial group is often associated with angular conjunctivitis and subconjunctival hemorrhages?

Moraxella species (B) Signup and view all the answers

Which of these bacterial species is NOT a common cause of bacterial conjunctivitis in adults?

Neisseria gonorrhoeae (A) Signup and view all the answers

Which bacteria is most commonly associated with contact lens related microbial keratitis?

Pseudomonas aeruginosa (B) Signup and view all the answers

Which of these bacteria is described as being microaerophilic and prefering to grow at 28 degrees?

Nocardia species (C) Signup and view all the answers

Which bacterial species is known to cause crystalline keratopathy?

Viridans Streptococci (C) Signup and view all the answers

Which of the following is a characteristic of Chlamydia trachomatis?

It is structurally similar to gram-negative bacteria. (A) Signup and view all the answers

Which species is a commensal of the conjunctival sac that belongs to the same species as diphtheria bacillus?

Corynebacterium xerosis (A) Signup and view all the answers

A patient with membranous conjunctivitis is most likely to be infected with which of the following bacteria?

Streptococcus pyogenes (A) Signup and view all the answers

What is the typical appearance of the eye during bacterial conjunctivitis?

Mucopurulent (C) Signup and view all the answers

Which bacteria is a common cause of hospital acquired infections?

Both Pseudomonas aeruginosa and MRSA (B) Signup and view all the answers

Which bacterial species is frequently associated with severe mucopurulent infection in microbial keratitis?

Streptococcus pneumoniae (C) Signup and view all the answers

Which of these bacterial species is NOT gram-positive?

Moraxella species (B) Signup and view all the answers

A bacterial corneal infection typically begins with:

A break through the corneal epithelium. (B) Signup and view all the answers

When examining E. coli cultures, what is the initial incubation temperature and duration before further action is required if no growth is observed?

37 degrees for 3-6 days (C) Signup and view all the answers

Which of these treatments would be classified as an antimicrobial agent?

PHMB (B) Signup and view all the answers

A patient presents with chronic epiphora. Upon examination, it's determined that the canaliculi are blocked promoting anaerobic conditions. Which condition is most likely?

Canaliculitis (C) Signup and view all the answers

Which of these bacteria is Gram-positive and anaerobic, and is found in cheesy concretions?

Actinomyces israelii (B) Signup and view all the answers

In cases of endophthalmitis, after obtaining samples, what agar types are primarily used for inoculation?

Chocolate, blood and Sabouraud's agar (A) Signup and view all the answers

What type of microorganism is most associated with chronic endophthalmitis, many weeks after cataract surgery?

Skin commensals (A) Signup and view all the answers

In the context of treating anterior segment microbial diseases, when would pathogen isolation be attempted?

When the disease is moderate, severe, or unresponsive to initial treatment (C) Signup and view all the answers

After isolating a bacterial pathogen, what is the main method used for testing antibiotic sensitivity?

Disc diffusion (C) Signup and view all the answers

What does a zone of inhibition around an antibiotic disc signify in a disc diffusion test?

Antibiotic sensitivity (A) Signup and view all the answers

What is the main difference between a bacteriostatic and a bactericidal antibiotic?

Bacteriostatic inhibits bacterial growth, while bactericidal inhibits growth AND destroys bacteria (B) Signup and view all the answers

If an infection is resistant to Gentamicin, which antibiotics from the table are listed as possible alternatives?

Amikacin and Ampicillin (A) Signup and view all the answers

Which of the listed antibiotics are primarily used to treat external bacterial infections, and are effective against Pseudomonas?

Gentamicin and Polymyxin B (A) Signup and view all the answers

What is the clinical use of Ceftazidime detailed in the text?

Used in conjunction with Polymyxin B + Neomycin in the conjunctiva (A) Signup and view all the answers

Which of these antibiotics is a quinolone antibiotic and is also effective against Pseudomonas?

Both Levofloxacin and Ofloxacin (A) Signup and view all the answers

Which of these options describes the use of Propamidine Isetionate/ Dipropamidine Isetionate?

An aromatic diamidine disinfectant, effective against most but more effective against Gram-positive (A) Signup and view all the answers

Study Notes

Anterior Segment Eye Microbiology

Certain microbes found elsewhere in the body may cause corneal infections.
Approximately 50% of ocular samples have micro-organisms.
The eyelids have a higher count of micro-organisms than the conjunctiva while the cornea and aqueous chamber are considered sterile.

Most Common Bacteria

Gram-positive, coagulase-negative staphylococci are prevalent.
Other isolates include Staphylococcus aureus, Micrococcus, Bacillus, and Bacteroides.
Gram-negative micro-organisms are less common, typically less than 5% of cases.

Bacterial Spectrum at Birth and Childhood

At birth, the bacterial spectrum differs from adulthood.
Within five days, bacterial spectrum becomes similar to adult patterns.
During childhood, streptococcal colonisation is more frequent.
Lactobacillus, Bifidobacterium, and Streptococcus are common.

Fungal Colonization

Fungal colonization is less common, typically occurring in eyelids between 2-52% and conjunctiva between 2-37%.
Number and frequency of gram-positive bacteria generally increase during sleep.

Sample Obtaining for Corneal Infections

Direct scraping of the corneal ulcer is carried out for smear and culture preparation using unpreserved topical anesthetic.
The base and leading edge are scraped using a spatula onto a glass slide and air-dried for staining.
For severe cases, a corneal biopsy might be needed.
Acanthamoeba and fungal investigations may involve in vivo confocal microscopy.
Contact lens samples can use the Agar Sandwich Technique to isolate bacteria within/on the lens.

Obtaining Sample for Viral Infections

Direct examination of tissue scrapes is needed
Cell culture to isolate causative organisms
PCR testing with specific microbial DNA sequences may be used for certain diseases.

Routine Lab Protocol

Direct microscopy of samples.
Bacterial cultures are incubated at 37 degrees for 24-48 hours (variable based on bacterial type).
Growth evaluation and antibiotic sensitivity tests follow.

Staining Techniques for Microscopy

Gram staining is a major method to identify bacteria.
Other techniques include Giemsa, Ziehl-Neelsen, fluorescent dyes, and immuno-peroxidase. Different methods may be used for different types of microbiology identification.

Bacterial Growth

Bacteria generally reproduce via binary fission.
Key phases include lag, exponential, stationary, and decline.
Growth curves track bacterial population over time.

Bacterial Microorganisms

Staphylococcus Aureus, Coagulase-Negative Staphylococci, Streptococci species, Gram Negative Rods (Corynebacterium species, Propionibacterium Acnes) are important bacterial microorganisms.

Fungal Growth

Moisture is essential for fungal growth.
Fungi absorb nutrients from the environment.

Broth Media

Broth media allows for growth of small numbers of organisms.
Broth media can also dilute residual antibiotics.

Different Types of Media

Blood agar is frequently used for various bacteria isolation and is commonly used in medical labs.
Chocolate agar is blood agar heated to 60 degrees. A specialized blood agar used to isolate Neisseria and Haemophilus species (bacteria).
Sabouraud’s agar supports isolation of fungi.

Ophthalmic Microorganism Specifics: Lids/Eyeballs

Specific bacterial types are common in lid/eye infections like staph aureus, streptococcus species, or haemophilus influenzae.
Specific samples collected should be mentioned in the associated study material regarding the exact location or source.

Microbial Keratitis (MK)

Microbial Keratitis (MK) can be caused by bacteria, viruses, fungi, and yeasts.
Different organisms are implicated including Staphylococcus Aureus, Coagulase-Negative Staphylococci, Streptococcus species, Pseudomonas species, Branhamella species, Proteus/Serratia species, and Haemophilus influenzae.
Fungus (Aspergillus Niger, Aspergillus Fumigatus, Fusarium) may be the cause.

Amoebic Keratitis

Amoebic keratitis (AK) is caused by free-living organisms found in water, mud, and water-cooling tanks.
Acanthamoeba polyphaga is the most common cause.

Endophthalmitis

Endophthalmitis is often post-operative/traumatic/or exogenous infections.
Samples of the vitreous and aqueous humor are tested for microbes (staph aureus, pseudomonas, enteric bacteria, strep).
Samples are ideally inoculated onto blood and Sabouraud's agar.

Bacterial Conjunctivitis

Conjunctivitis can be caused by various bacteria; important microorganism examples in both the adult and child include staph aureus, streptococcus pneumonia, haemophilus influenzae, and pseudomonas.

Antibiotic Treatment

Antibiotic sensitivity testing is important to direct appropriate treatment.
Broad-spectrum and narrow-spectrum antibiotics are used depending on the suspected organisms.
Correct antibiotic choice is needed based on the identified causative bacteria.

Treatment of Microbial Keratitis

Intensive therapy (antibiotic) and/or corticosteroids are often necessary for immediate action.
Antibiotic sensitivity tests should be conducted to guide the most appropriate choice of antibacterial therapy
Options may include topical antibiotics or systemic treatments.

Viral, Fungal, and Amoebic Infections Treatment

Acylovir, azoles, miconazole, and ketoconazole are typical therapeutic agents used against respective infections.
Some infections may require additional treatments including surgery or hospitalisation.

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Description

Test your knowledge on the microbial presence in the eye and the common bacterial isolates found in eyelids and conjunctiva. This quiz also covers methods for analyzing infections and techniques such as Gram staining and PCR testing. Dive into the fascinating world of ocular microbiology.