bacterial ocular infections and antibiotics Flashcards
(28 cards)
What are Gram-positive bacteria, and what distinguishes them from Gram-negative bacteria?
Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain, making them appear purple under a microscope. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, which makes them stain pink after the Gram stain procedure.
What is the role of pili in bacterial infections?
Pili are used by bacteria for attachment to host cells and surfaces. They play a role in colonisation and pathogenesis. Conjugation pili also facilitate the transfer of plasmids (including antibiotic resistance genes) between bacterial cells.
What is the mechanism of biofilm formation in bacteria?
Biofilm formation occurs when bacteria aggregate on a surface, surrounded by an extracellular matrix of polysaccharides, proteins, and nucleic acids. This protects bacteria from immune responses, antibiotics, and environmental stress, making infections harder to treat.
What are the main characteristics of Staphylococcus aureus?
Gram-positive cocci, arranged in clusters.
Causes skin infections (boils, impetigo), conjunctivitis, and keratitis.
Can form abscesses and contribute to systemic infections like sepsis.
Coagulase-positive, making it able to clot plasma.
What types of ocular infections can Staphylococcus aureus cause?
Staphylococcus aureus can cause bacterial keratitis, conjunctivitis, styes, and endophthalmitis. It is a major cause of contact lens-associated infections and post-surgical ocular infections.
What are the main characteristics of Pseudomonas aeruginosa?
Gram-negative rod with a blue-green pigment due to the production of pyocyanin.
Found in moist environments like soil, water, and hospital settings.
Known for its virulence and ability to form biofilms.
Causes keratitis (especially in contact lens wearers), pneumonia, and wound infections.
How does Pseudomonas aeruginosa contribute to ocular infections?
Pseudomonas aeruginosa is a common cause of contact lens-associated keratitis, particularly in non-compliant lens users. It leads to corneal ulceration, which can result in permanent visual damage if not treated promptly.
What is the role of antibiotics in the treatment of bacterial ocular infections?
Antibiotics are used to treat bacterial ocular infections by inhibiting bacterial growth (bacteriostatic) or directly killing bacteria (bactericidal). Common antibiotics for ocular infections include fluoroquinolones, aminoglycosides, and macrolides.
What is the mechanism of action of beta-lactam antibiotics?
Beta-lactam antibiotics (e.g., penicillin) inhibit peptidoglycan synthesis by binding to penicillin-binding proteins (PBPs), which are crucial for cell wall formation. This leads to bacterial lysis.
How does Pseudomonas aeruginosa develop antibiotic resistance?
Pseudomonas aeruginosa develops antibiotic resistance through various mechanisms:
Efflux pumps that expel antibiotics out of the cell.
Beta-lactamase production, which degrades beta-lactam antibiotics.
Mutations in target sites for antibiotics, making them less effective.
What are antibiotic resistance genes, and how are they transferred between bacteria?
Antibiotic resistance genes are genes that enable bacteria to survive in the presence of specific antibiotics. These genes are often carried on plasmids and can be transferred between bacteria via conjugation, transduction, or transformation
What is the significance of Gram stain in identifying bacterial infections?
The Gram stain helps differentiate bacteria into Gram-positive (purple) and Gram-negative (pink) groups based on their cell wall structure. It aids in identifying the type of bacteria and helps guide antibiotic treatment by indicating whether the bacteria will respond to certain antibiotics (e.g., beta-lactams for Gram-positive bacteria).
What is the difference between bactericidal and bacteriostatic antibiotics?
Bactericidal antibiotics kill bacteria directly (e.g., penicillin, aminoglycosides).
Bacteriostatic antibiotics inhibit bacterial growth and reproduction, relying on the immune system to clear the infection (e.g., tetracyclines, macrolides).
How do fluoroquinolones work as antibiotics?
Fluoroquinolones inhibit DNA gyrase and topoisomerase IV, enzymes involved in DNA replication and repair, thereby preventing bacterial cell division and growth.
What is biofilm formation, and why is it clinically significant?
Biofilm formation occurs when bacteria aggregate on surfaces, producing an extracellular matrix that protects them from antibiotics and immune responses. This contributes to chronic infections and is particularly problematic in ocular infections like keratitis and endophthalmitis.
How does antibiotic resistance impact the management of ocular infections?
Antibiotic resistance makes the treatment of ocular infections more challenging by reducing the effectiveness of commonly used antibiotics, leading to treatment failure and prolonged infections. It requires more potent or broad-spectrum antibiotics and increases the risk of complications.
What is the role of topical antibiotics in the treatment of ocular infections?
Topical antibiotics are commonly used to treat superficial ocular infections, such as conjunctivitis and keratitis. They are applied directly to the eye, providing localised treatment while minimising systemic side effects.
What are the common signs and symptoms of a bacterial ocular infection?
Symptoms include redness, pain, discharge, photophobia, and swelling. In more severe cases, vision changes, corneal ulcers, and blurred vision may be present.
How are ocular infections diagnosed?
Ocular infections are diagnosed through clinical examination, culture and gram staining of ocular specimens (e.g., corneal scrapings), and sometimes PCR (Polymerase Chain Reaction) to identify specific pathogens.
What are the general treatment strategies for bacterial keratitis?
Treatment for bacterial keratitis typically involves broad-spectrum topical antibiotics like fluoroquinolones. In severe cases, hospitalisation, corneal transplant, or intravenous antibiotics may be required.
What are some prevention strategies to avoid bacterial ocular infections?
Prevention includes proper contact lens hygiene, avoiding sharing eye makeup, using sterile equipment for ocular procedures, and practicing good hand hygiene.
‘bacteraemia’?
Bacterial infection of the blood
the shape of Staphylococcus
aureus?
Spherical
risk factor for Staphylococcus
keratitis?
Immunocompromised
Diabetes
LASIK eye surgery
Eyelid abnormalities
