Ocular Microbiology Overview
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Questions and Answers

Which of the following is a characteristic of Streptococcus pneumoniae?

  • Gram-negative cocci
  • Gram-positive, alpha-haemolytic cocci (correct)
  • Beta-haemolytic
  • Gram-negative rods

What is a common presentation of Neisseria gonorrhoeae conjunctivitis?

  • Commensal of the naso-pharynx
  • Mild, watery discharge
  • Angular conjunctivitis with limited corneal involvement
  • Severe, haemorrhagic, muco-purulent discharge (correct)

Which bacterial species is most frequently isolated in cases of microbial keratitis (MK) in the UK based on the information provided?

  • _Staphylococcus aureus_ (correct)
  • _Moraxella osloensis_
  • _Streptococcus pneumoniae_
  • _Neisseria gonorrhoeae_

What is the typical morphology and gram stain reaction of Moraxella species?

<p>Gram-negative rods (D)</p> Signup and view all the answers

Which patients are described as particularly vulnerable to microbial keratitis (MK)?

<p>Immunosuppressed individuals (B)</p> Signup and view all the answers

What is the primary recommended treatment for patients with severe microbial keratitis (MK), as detailed in the text?

<p>Hospital admission for intense topical antibiotic treatment (D)</p> Signup and view all the answers

What is an accurate description of Neisseria gonorrhoeae based on the text provided?

<p>Gram-negative cocci often seen intracellularly (C)</p> Signup and view all the answers

Besides Haemophilus influenza and Staph. aureus, which other bacterium is specifically mentioned as a cause of anterior segment eye conditions?

<p><em>Neisseria gonorrhoeae</em> (D)</p> Signup and view all the answers

What is the primary treatment purpose for Polymyxin B?

<p>Topical treatment for eye infections caused by susceptible strains of Pseudomonas (C)</p> Signup and view all the answers

Which antibiotic is noted as being effective against infections caused by Pseudomonas?

<p>Ticarcillin (D)</p> Signup and view all the answers

What type of bacteria is Amikasin particularly effective against?

<p>Gram-negative bacteria resistant to gentamicin (C)</p> Signup and view all the answers

Which statement about Tetracycline is correct?

<p>It is effective against both Gram-positive and Gram-negative bacteria, and some protozoa. (B)</p> Signup and view all the answers

What does the presence of resistance in Bacitracin zinc indicate?

<p>Penicillinase production by the organism (A)</p> Signup and view all the answers

Which organism is primarily responsible for acute microbial keratitis (MK) and can severely scar the cornea?

<p>Fusarium species (A)</p> Signup and view all the answers

Which bacteria, although of low pathogenicity, can cause severe MK and is sensitive to a wide range of antibiotics?

<p>Moraxella species (A)</p> Signup and view all the answers

What is the typical causative organism isolated from patients with fungal keratitis?

<p>Candida albicans (D)</p> Signup and view all the answers

Which type of organism is typically associated with free-living amoebic keratitis (MK)?

<p>Amoebae (B)</p> Signup and view all the answers

Which species are primarily responsible for MK in immunocompromised patients and have been reported in very few cases?

<p>Proteus and Serratia species (B)</p> Signup and view all the answers

What is a key characteristic of Nocardia species in relation to their pathogenicity?

<p>They are microaerophilic and grow at 28°C. (C)</p> Signup and view all the answers

Which species has been found occasionally as an isolate in cases of conjunctivitis, though it is more commonly associated with other infections?

<p>Haemophilus influenzae (B)</p> Signup and view all the answers

Which of the following statement about Candida species in MK is correct?

<p>They must be treated with antifungals. (C)</p> Signup and view all the answers

What is the primary effective agent against prions mentioned?

<p>Bleach (5% sodium hypochlorite) (A)</p> Signup and view all the answers

Which sterilization method is NOT primarily affected by heat?

<p>Ethylene oxide vapour (A)</p> Signup and view all the answers

What is the mechanism of ethylene oxide as a sterilizing agent?

<p>It attaches alkyl groups to biochemical structures. (D)</p> Signup and view all the answers

Which type of bacteria is more sensitive to gamma irradiation?

<p>Gram-negative bacteria (C)</p> Signup and view all the answers

What characteristic of Deinococcus radiodurans contributes to its high radiation resistance?

<p>Efficiency in repairing double-stranded DNA breaks (D)</p> Signup and view all the answers

Which of the following is a consequence of invading micro-organisms?

<p>Endophthalmitis (A)</p> Signup and view all the answers

Which sterilization method can potentially disrupt biochemical molecules?

<p>Gamma irradiation (D)</p> Signup and view all the answers

Which spores are known to be more resistant to radiation due to protective proteins?

<p>Bacillus and Clostridium spores (D)</p> Signup and view all the answers

What is the primary aim of therapeutic strategies in treating microbial keratitis?

<p>To eradicate the infectious agent and modulate immune response. (A)</p> Signup and view all the answers

Which antibiotic is specifically NOT suitable for treating Pseudomonas infections?

<p>Chloramphenicol (D)</p> Signup and view all the answers

What is an advantage of topical instillation of antimicrobial agents?

<p>Decreased likelihood of toxic effects compared to oral antibiotics. (D)</p> Signup and view all the answers

How often should antibiotic drops be instilled during the initial management of microbial keratitis?

<p>Every 30 minutes to 1 hour. (C)</p> Signup and view all the answers

Cefuroxime is classified as what type of antibacterial agent?

<p>Systemic broad-spectrum antibiotic. (D)</p> Signup and view all the answers

Which of the following antibiotics is used topically in combination with Polymyxin B and neomycin?

<p>Ceftazidime (A)</p> Signup and view all the answers

What is the preferred method of delivering antibiotics for less systemic toxicity in treating infections?

<p>Topical instillation. (D)</p> Signup and view all the answers

What is the potential consequence of systemic absorption of eye drops?

<p>Risk of systemic toxicity. (B)</p> Signup and view all the answers

What is the purpose of using broad spectrum antibiotics in empirical therapy?

<p>To provide activity against common causative agents (D)</p> Signup and view all the answers

Why might up to 50% of microbial keratitis (MK) cases be culture negative?

<p>The pathogens may not be present in sufficient numbers (B)</p> Signup and view all the answers

What is typically assessed after isolating the infecting micro-organism?

<p>The antibiotic sensitivity of the organism (A)</p> Signup and view all the answers

How are antibiotics classified into broad spectrum and narrow spectrum?

<p>By their activity against a range of bacteria or specific organisms (B)</p> Signup and view all the answers

What are bacteriostatic antibiotics designed to do?

<p>Inhibit the growth of bacteria (D)</p> Signup and view all the answers

What does a marked difference in the zones of inhibition compared to the control indicate?

<p>The test organism is resistant to the antibiotics (C)</p> Signup and view all the answers

Which of the following is NOT typically tested for antibiotic sensitivity?

<p>Viruses (A)</p> Signup and view all the answers

What organism is primarily identified in endophthalmitis according to the smear?

<p>Candida parapsilosis (D)</p> Signup and view all the answers

Flashcards

Moraxella species

Gram-negative rods that commonly cause angular conjunctivitis and are found in the naso-pharynx.

Streptococcus pneumoniae

Gram-positive, alpha-hemolytic, pyogenic cocci.

Neisseria gonorrhoeae

Gram-negative cocci often found inside cells, causing severe, bloody, pus-filled conjunctivitis that can affect the cornea.

Staphylococcus aureus

A common cause of bacterial keratitis, this bacteria is found in over 50% of cases in the UK.

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Coagulase-negative staphylococci

There are over 40 types of these Gram-positive bacteria, which are a common cause of bacterial keratitis.

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Bacterial keratitis (MK)

A serious infection of the cornea that can lead to vision loss and blindness.

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Treatment for bacterial keratitis

Patients with MK should be admitted to the hospital for intensive topical treatment with fortified antibiotics.

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Staphylococcus aureus

The most common cause of bacterial keratitis, this Gram-positive bacteria is often found in hospital settings.

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What are Moraxella species?

Gram-negative diplo-bacilli that cause severe corneal infections, but are sensitive to a wide range of antibiotics. The cornea is slow to heal after infection.

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What are Proteus and Serratia species?

Gram-negative rods that can cause corneal infections, but are rarely reported. They are more common in patients with weakened immune systems.

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What are Fusarium species?

Gram-negative rods that can cause severe corneal infections and leave the cornea scarred. They are often found in patients who have been infected abroad.

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What are Nocardia species?

Gram-positive rods that are pleomorphic, microaerophilic, and grow best at 28°C. They are rarely associated with corneal infections, but can be found in immunosuppressed patients.

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What are yeasts?

Single round bodies that reproduce by budding. They are often found in patients with pre-existing infections or weakened immune systems.

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What is Candida albicans?

A species of yeast that can be found in the digestive system. This specific species is the most common cause of corneal infections in patients with weakened immune systems.

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What are amoebae?

Free-living organisms found in water, mud, and water-cooling tanks. These organisms can cause corneal infections.

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What is Haemophilus influenzae?

A common bacterial cause of conjunctivitis that can occasionally cause corneal infections.

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Broad-spectrum antibiotic

A type of antibiotic effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.

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Microorganism identification

The process of identifying the specific type of microorganism causing an infection.

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Antibiotic sensitivity testing

A test that determines which antibiotics are most effective against a particular microorganism.

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Narrow-spectrum antibiotic

Antibiotics that mainly target specific types of bacteria.

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Empirical antibiotic therapy

An antibiotic given to treat a suspected infection before the causative microorganism is identified.

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Bacteriostatic antibiotic

Antibiotics that inhibit the growth of microorganisms.

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Bactericidal antibiotic

Antibiotics that kill microorganisms directly.

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Disk diffusion method

Determining the effectiveness of an antibiotic against a bacterial isolate by measuring the size of the zone of inhibition around an antibiotic disk.

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Amikacin

An antibiotic effective against serious Gram-negative infections resistant to gentamicin.

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Tetracycline

A systemic antibacterial often used for blepharitis infections. Effective against Gram-positive and Gram-negative bacteria, and some protozoa.

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Propamidine isetionate/Diprom/Propramidine isetionate

A topical aromatic diamidine disinfectant effective against Gram-positive bacteria, less effective against Gram-negative bacteria.

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Ticarcillin

A systemic antibacterial effective against infections due to Pseudomonas and Proteus spp.

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Bacitracin zinc

A systemic antibacterial that is not often used, but resistance to this antibiotic indicates penicillinase production by the organism.

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Autoclaving

A sterilization method that uses high-temperature steam under pressure to kill microorganisms. It is effective for most microorganisms but may not inactivate resistant agents like prions.

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Ethylene oxide sterilization

A chemical sterilant that uses ethylene oxide gas to kill microorganisms. It is effective against a wide range of microorganisms, including spores, but it is toxic and requires specialized equipment.

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Gamma irradiation

A sterilization method that uses ionizing radiation to kill microorganisms. It is effective against a wide range of microorganisms, including spores, and is often used for sterilizing medical devices and pharmaceuticals.

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Deinococcus radiodurans

A type of bacteria that is particularly resistant to radiation due to its efficient DNA repair mechanisms.

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Microbial recovery and identification

The process of recovering and identifying microorganisms from clinical samples.

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Ceftazidime

A type of antibiotic, used to treat microbial keratitis, that is often combined with Polymyxin B and neomycin.

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Chloramphenicol

A broad-spectrum antibiotic that is often used to treat conjunctivitis.

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Ciprofloxacin

A quinolone antibiotic with a broad spectrum of activity, often used to treat both gram-negative and staphylococcal infections.

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Cefuroxime

A systemic antibiotic with broad-spectrum activity used to treat a variety of bacterial infections.

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Chloramphenicol

An antibiotic that can be administered both topically and systemically, and is a common choice for conjunctivitis treatment. However, it is not suitable for Pseudomonas infections.

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Ceftazidime

An anti-bacterial agent that is a popular choice for treating microbial keratitis. It is often used in conjunction with Polymyxin B and neomycin.

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Treatment of Microbial Keratitis

The main aims of treating microbial keratitis are to eradicate the infectious agent with anti-microbial compounds and to modulate the host immune response.

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Erythromycin

A popular systemic antibiotic often used to treat bacterial infections.

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Study Notes

Ocular Microbiology

  • Ocular infections are caused by a wide range of microorganisms.
  • Many harmless microbes are normally present in the eye, but can become pathogenic.
  • Understanding the normal ocular biota and the effects of disinfection/sterilization is important for clinical optometry.

Microbiology of Anterior Segment Eye Conditions

  • The ocular surface is sparsely colonized.
  • The lid margin and conjunctiva are colonized by Gram-positive bacteria (e.g., coagulase-negative Staphylococci, Corynebacteria, Propionibacterium).
  • Gram-negative bacteria are less common.
  • The cornea and anterior chamber are considered sterile.
  • The normal microbial flora of other mucous membranes is different and more diverse (than the eye).

Obtaining Samples

  • Microbial analysis requires scraping the cornea for infection samples.
  • Samples may include the bulbar conjunctiva, fornices, and eyelids with moistened cotton swabs/calcium alginate.
  • Topical anesthetics are preferable to avoid the effects of preservatives.

Routine Laboratory Protocol

  • Direct microscopy is performed first.
  • Culture media is inoculated with samples and incubated at 37°C.
  • The samples are examined at 24 & 48 hours and if necessary, antibiotic susceptibility tests are performed.
  • Staining techniques (e.g., Gram stain) are used to identify bacteria.

Bacterial Growth

  • Bacterial growth has four phases (lag, logarithmic, stationary, and decline).
  • The stages of growth are important to understand to make a diagnosis.
  • Bacteria reproduce asexually by binary fission.

Gaseous Requirements

  • Aerobic bacteria require a normal atmosphere.
  • Anaerobic bacteria require an oxygen-free environment, and
  • Microaerophilic bacteria require less oxygen, as well as facultative anaerobes.
  • Some bacteria (fastidious) require additional CO2 for growth.

Bacteriological Media

  • Media must contain carbon and nitrogen sources, as well as salts and water.
  • Agar is used to solidify the media.
  • Different type of media are used to encourage (enrichment), selectively grow specific bacteria, or inhibit other microorganism growth (selective media).

Fungal Growth

  • Fungi are easy to grow – often on a simple media or bread in a warm, moisture environment.

Staining for Microscopy

  • Various staining methods (Gram stain, Giemsa) detect different microorganisms depending on their characteristics.
  • Gram stain identifies Gram-positive (blue) or Gram-negative (red) bacteria.

Microorganism Isolation

  • Culturing, methods and specific media (blood agar, chocolate agar, Sabouraud's agar) support the growth of a wide range of bacteria, including fastidious microbes, such as fungi or Neisseria.

Bacteria Causing Ocular Infections

  • Table 1 shows various organisms associated with different parts of the eye.
  • Organisms differ depending on the age of the patient, site of infection, types of infection.

Ocular Diseases

  • Blepharitis (lid margin), conjunctivitis (conjunctiva), keratitis (cornea), etc. are caused by several microbes.
  • The causative microorganisms differ for various ocular diseases.
  • Table 1 lists the microbes that commonly cause eye conditions with regard to the area of the eye.

Important Microbes

  • Staph. aureus and coagulase-negative staphylococci are frequent causes of blepharitis.
  • Neisseria gonorrhoeae can cause neonatal conjunctivitis.
  • Various other bacteria can lead to various eye conditions.
  • Pseudomonas aeruginosa is a common cause of contact lens-associated keratitis.

Microbial Keratitis (MK)

  • Microbes can infect the cornea (MK).
  • The infections can be caused by various microbes.
  • Some microbes are more likely to be present in the environment with regards to where the patients are coming from.
  • Culture-guided therapy (using identified microbes and their sensitivities as a guide) can be used to determine the most effective drugs.
  • Patients with poor immunity are more susceptible to severe fungal keratitis.

Fungal Microbes

  • Fungi, such as Aspergillus and Fusarium, can cause MK.
  • Specific fungal infections may result if the patient comes from certain areas or has compromised immunity.

Amoebic Keratitis

  • Amoeba can cause MK, including Acanthamoeba species.
  • Treatment and prevention methods are crucial because these microbes can be difficult or slow to treat.

Hypopyon, Endophthalmitis

  • These are severe anterior segment eye conditions.
  • These conditions are often caused by Staph. aureus, Strep. pneumoniae, and other gram negative microbes.
  • Samples are taken from aqueous or vitreous (eye fluids) with treatment involving using several types of antimicrobials.

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Ophthalmic Medical Microbiology PDF

Description

This quiz covers the fundamental aspects of ocular microbiology, particularly focusing on ocular infections caused by various microorganisms. It includes information about the normal microbial flora of the eye, conditions impacting the anterior segment, and methods for obtaining samples for microbial analysis.

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