Culture & Sensitivity, Aerobic bacteria Eye Samples( Vitek 2 Compact)

Bacterial/ Viral

Report in 72Hrs

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No Fasting Required

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Identifies bacteria & antibiotic susceptibility.

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Culture & Sensitivity Aerobic bacteria Eye Samples (Vitek 2 Compact) - Comprehensive Medical Guide

1. Why is it done?
- Test Purpose: This test identifies and isolates aerobic bacterial pathogens from ocular (eye) samples and determines their susceptibility to various antimicrobial agents using the Vitek 2 Compact automated microbiology system.
- Primary Indications for Ordering: • Suspected bacterial conjunctivitis (inflammation of the conjunctiva) • Suspected bacterial keratitis (corneal infection) • Eye infections following ocular trauma or surgery • Recurrent or persistent eye infections not responding to empirical therapy • Suspected dacryocystitis (tear duct infection) • Post-operative eye infections • Contact lens-related infections • Suspected endophthalmitis (infection inside the eye) • Chronic eye discharge of unknown etiology • Immunocompromised patients with eye infections
- Typical Timing and Circumstances: • When a patient presents with acute or chronic eye infection symptoms • Before initiating antibiotic therapy in severe infections • When initial antibiotic treatment has failed • In hospital-acquired (nosocomial) eye infections • As part of infection control monitoring in healthcare settings • Within 24-48 hours of symptom onset for optimal culture yield
2. Normal Range
- Normal Results: • No growth or "No aerobic bacteria isolated" • Absence of clinically significant pathogens • Normal conjunctival flora may include: Coagulase-negative Staphylococcus, Corynebacterium species, or Propionibacterium species
- Units of Measurement: • Colony Forming Units per milliliter (CFU/mL) • Bacterial identification reported as organism species • Antibiotic susceptibility reported as: Susceptible (S), Intermediate (I), or Resistant (R)
- How to Interpret Results: • Negative (No Growth): Indicates no clinically significant bacterial infection; normal findings • Positive (Growth Detected): Identifies the causative organism and provides antibiotic susceptibility profile • Light Growth (1+ to 2+): May indicate contamination or colonization; clinical context is important • Heavy Growth (3+ to 4+): Suggests significant infection requiring treatment • Mixed Flora: May indicate contamination or polymicrobial infection; clinical correlation needed • Susceptible (S): Organism will respond to the antibiotic at standard doses • Intermediate (I): Organism may respond at higher antibiotic concentrations; clinical judgment required • Resistant (R): Organism will not respond to the antibiotic; alternative therapy needed
3. Interpretation
- Common Bacterial Pathogens and Clinical Significance: • Staphylococcus aureus: Associated with acute bacterial conjunctivitis, keratitis, and stye infections; often susceptible to beta-lactams • Streptococcus pneumoniae: Causes purulent conjunctivitis and keratitis; resistance patterns variable • Pseudomonas aeruginosa: Common in contact lens-related infections and corneal ulcers; often resistant to many antibiotics • Haemophilus influenzae: Causes acute conjunctivitis; usually susceptible to fluoroquinolones • Moraxella catarrhalis: Associated with mild to moderate conjunctivitis • Neisseria gonorrhoeae: Causes severe purulent conjunctivitis; requires systemic and topical therapy • Chlamydia trachomatis: Important cause of conjunctivitis in neonates and adults; requires systemic treatment
- Factors Affecting Results and Interpretation: • Prior antibiotic use: May inhibit organism growth or selection of resistant strains • Sampling technique: Improper collection may result in contamination or insufficient sample • Sample preservation: Transport time and temperature affect bacterial viability • Time to processing: Delayed processing may reduce culture sensitivity • Topical anesthetics or preservatives: May inhibit bacterial growth • Ocular surface condition: Dry eye or severe inflammation may affect culture yield • Immune status of patient: Immunocompromised patients may have atypical presentations • Environmental contamination: Flora from skin may contaminate ocular samples
- Vitek 2 Compact System Advantages: • Rapid identification (2-18 hours depending on organism) • Automated susceptibility testing (AST) results • Reduced hands-on time and improved accuracy • Comprehensive antibiotic panel assessment • High accuracy in organism identification • Real-time results available for appropriate therapy selection
- Clinical Significance of Result Patterns: • Single pathogen growth: Suggests primary infection; organism and susceptibilities guide treatment • Multiple organisms: May indicate mixed infection, contamination, or polymicrobial disease • No growth with clinical symptoms: Consider viral, fungal, or chlamydial etiology; repeat culture if indicated • Multi-drug resistant organisms (MDROs): May require specialty antibiotics or consultation with infectious disease • Culture from post-operative infections: Helps identify nosocomial pathogens and guide infection control measures
4. Associated Organs
- Primary Organ System Involved: • Eye (Ocular system) • Conjunctiva (mucous membrane covering the white part of the eye and inner eyelid) • Cornea (clear outer layer of the eye) • Eyelids and tear ducts • Intraocular structures (if infection spreads internally)
- Medical Conditions Associated with Abnormal Results: • Bacterial Conjunctivitis: Acute infection causing redness, discharge, and irritation • Bacterial Keratitis: Serious corneal infection that can lead to vision loss • Blepharitis: Inflammation of the eyelid margins with bacterial involvement • Hordeolum (Stye): Acute bacterial infection of eyelid glands • Dacryocystitis: Infection of the tear sac • Endophthalmitis: Serious intraocular infection following surgery or trauma • Contact Lens-Associated Keratitis: Often associated with Pseudomonas aeruginosa • Post-operative Ocular Infections: Following cataract, refractive, or other eye surgery • Ocular Surface Disease with Secondary Infection • Gonococcal Conjunctivitis: Sexually transmitted infection causing severe eye disease
- Potential Complications and Risks of Abnormal Results: • Permanent corneal scarring and visual impairment • Vision loss or blindness if infection not treated promptly • Corneal perforation and globe rupture • Spread to intraocular structures (uveal tract, retina) • Secondary glaucoma from inflammatory changes • Orbital cellulitis from spread of infection beyond the eye • Meningitis (especially with gonococcal or meningococcal infection) • Systemic bacteremia and sepsis • Chronic inflammation and dry eye syndrome • Secondary infection with opportunistic organisms • Pseudomonas-related complications: rapid corneal melting and perforation • Antibiotic resistance complications requiring escalated therapy
- Related Systemic Conditions: • Immunocompromise (HIV/AIDS, organ transplant, chemotherapy) • Diabetes mellitus (increased infection susceptibility) • Rheumatoid arthritis (scleritis association) • Ocular cicatricial pemphigoid • Stevens-Johnson syndrome • Graft versus host disease (in transplant patients)
5. Follow-up Tests
- Additional Tests Based on Positive Results: • Repeat Culture: If initial treatment fails or to confirm clearance of infection • Gram Stain: For rapid identification of gram-positive vs gram-negative organisms • Fungal Culture: If fungal infection suspected alongside bacterial infection • Viral Culture or PCR: If viral conjunctivitis is suspected • Chlamydia trachomatis Testing: If chlamydial infection is suspected (not detected in routine bacterial culture) • Syphilis Testing (RPR/VDRL): In cases of gonococcal conjunctivitis • Gonorrhea Testing (PCR/Nucleic Acid Amplification): For suspected gonococcal infection confirmation • Blood Culture: If systemic sepsis is suspected or in severe infections like endophthalmitis
- Further Investigations and Diagnostic Imaging: • Slit-lamp Biomicroscopy: To assess severity of ocular inflammation and corneal involvement • Confocal Microscopy: To visualize bacterial presence on cornea • Ocular Ultrasound: If endophthalmitis suspected or if media opacity prevents visualization • CT/MRI Orbits: To exclude orbital cellulitis or abscess formation • Anterior Segment Photography: To document disease progression or treatment response
- Monitoring Frequency for Ongoing Conditions: • Acute Bacterial Conjunctivitis: Clinical reassessment every 2-3 days; repeat culture if no improvement after 48-72 hours of appropriate therapy • Bacterial Keratitis: Daily evaluation; culture may be repeated if worsening despite treatment • Post-operative Infections: Frequent ophthalmologic evaluation as clinically indicated; culture at 48-72 hours if poor response • Contact Lens-Related Infections: Close follow-up during and after treatment; monthly monitoring if recurrent • Chronic Infections: Quarterly or as clinically indicated based on symptom progression • Hospital-Acquired Infections: Surveillance cultures if indicated per infection control protocols
- Related Complementary Tests: • Extended Spectrum Beta-Lactamase (ESBL) Testing: If resistant gram-negative organisms detected • Methicillin-Resistant Staphylococcus aureus (MRSA) Screening: If resistant Staph aureus identified • Carbapenem-Resistant Enterobacteriaceae (CRE) Testing: For highly resistant organisms • In Vitro Synergy Testing: For polymicrobial infections to guide combination therapy • Anaerobic Culture: If anaerobic infection suspected (rare in ocular infections) • Complete Blood Count (CBC): To assess systemic response to infection • C-Reactive Protein (CRP): To monitor systemic inflammatory response
6. Fasting Required?
- Fasting Requirement:NO
- Special Instructions and Patient Preparation: • No fasting is required for this test • The test involves collection of ocular secretions or specimens from the eye surface • No special dietary preparations are necessary
- Medications to Avoid Before Test: • Topical anesthetics: Should NOT be used prior to collection as they inhibit bacterial growth and compromise culture results • Topical antibiotics: Should be withheld 24-48 hours before culture collection when possible to avoid suppressing organism growth • Ocular lubricants with preservatives: May interfere with culture; artificial tears without benzalkonium chloride are preferred • Contact lens solutions: Remove contact lenses at least 1-2 hours before culture collection • Cosmetics or eye makeup: Should be removed before specimen collection • Antimicrobial eye drops: Discontinue if possible before culture to improve sensitivity
- Specimen Collection Requirements: • Patient should avoid touching or rubbing eyes before collection • Hands should be washed before and after collection • Specimens should be collected from the lower fornix (bottom of the eye) using sterile swabs or by expressing discharge • Multiple swabs from both eyes may be taken for bilateral infections • Specimens must be placed in appropriate sterile collection tubes or on sterile transport media • Collection should avoid the eyelashes and eyelid margins to prevent contamination • Specimens should be labeled with patient identifiers and site of collection (right eye OD or left eye OS)
- Transport and Processing Requirements: • Specimens should be transported immediately to the laboratory • Should not be refrigerated as this may reduce bacterial viability • Keep at room temperature (15-30°C) during transport • Processing should occur within 2 hours of collection when possible • Use appropriate transport media to maintain specimen viability • Do not allow specimens to dry out • Specimens should not be frozen unless processing will be delayed beyond 2 hours
- Pre-Procedure Patient Communication: • Inform patient that specimen collection is minimally uncomfortable • Explain that some eye discharge may be expressed during collection • If topical anesthetic is used for collection, warn patient of temporary numbness • Advise patient to avoid eye contact with others during and immediately after collection • Instruct patient to wash hands after collection • Advise that results typically available in 24-48 hours • Explain that preliminary results may be available in 18-24 hours • Inform patient about the importance of specimen collection before starting antibiotic therapy when possible

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