Introduction

Keratoconjunctivitis is a dual inflammation of the cornea and conjunctiva, and can be caused by various infectious and non-infectious agents. Among the infectious causes, bacterial aetiology is particularly significant due to its potential for rapid progression and ocular morbidity. Bacterial keratoconjunctivitis commonly affects all age groups and is especially prevalent in settings of poor hygiene, contact lens wear, or trauma to the ocular surface.

Early recognition and appropriate antimicrobial treatment are essential to avoid complications such as corneal scarring, perforation, or permanent vision loss. This article explores the bacterial organisms most frequently implicated in keratoconjunctivitis and discusses standard and emerging therapeutic options.

Aetiology and epidemiology

Bacterial keratoconjunctivitis is most commonly caused by Gram-positive cocci and Gram-negative bacilli. The prevalence of specific pathogens may vary by age group, geographical location, and risk factors.

Common bacterial pathogens

• Staphylococcus aureus and Coagulase-negative staphylococci

Staphylococcus aureus, including methicillin-resistant strains (MRSA), is a leading cause of bacterial keratoconjunctivitis globally. It commonly colonises the eyelid margins and lashes, and can breach the ocular surface through minor trauma or contact lens wear.¹ Coagulase-negative staphylococci, though generally less virulent, also contribute to infections, particularly in immunocompromised individuals.

• Streptococcus pneumoniae

This encapsulated Gram-positive coccus is a common pathogen in children and can cause acute purulent conjunctivitis with keratitis. It is more common in colder climates and often associated with upper respiratory tract infections.²

• Haemophilus influenzae

More prevalent in paediatric populations, Haemophilus influenzae can cause hyperacute conjunctivitis with profuse purulent (pus) discharge and is often associated with otitis media.³

• Pseudomonas aeruginosa

This Gram-negative bacillus is notorious for causing severe keratitis, particularly among contact lens wearers. It produces proteases and exotoxins that can rapidly degrade corneal tissue, making timely treatment crucial.⁴

• Neisseria gonorrhoeae

This sexually transmitted pathogen can cause hyperacute keratoconjunctivitis with rapid onset, profuse purulent discharge, and potential for corneal perforation. It requires systemic antibiotic therapy in addition to topical agents.⁵

• Chlamydia trachomatis

Although technically an obligate intracellular bacterium, C. trachomatis is responsible for trachoma and adult inclusion conjunctivitis, both of which may involve the cornea.⁶ Chronic infection can lead to conjunctival scarring and blindness if untreated.

Pathophysiology

Bacterial pathogens invade the conjunctival and corneal epithelium, triggering an inflammatory response characterized by leukocyte infiltration, cytokine release, and tissue damage. In some cases, bacterial toxins and enzymes such as elastases (notably in Pseudomonas infections) contribute to rapid corneal necrosis and ulceration.⁷

The virulence of the infecting organism, the patient’s immune status, and environmental or mechanical factors such as trauma or contact lens use all influence the clinical outcome.

Clinical presentation

Symptoms of bacterial keratoconjunctivitis include:

• Redness
• Tearing or mucopurulent discharge
• Photophobia
• Foreign body sensation
• Decreased visual acuity (in corneal involvement)
• Lid oedema

On examination, signs may include conjunctival injection, chemosis, corneal epithelial defects, stromal infiltrates, and anterior chamber reaction.

Diagnosis

Clinical evaluation

Diagnosis is primarily clinical, based on history and ocular examination using slit-lamp biomicroscopy. However, distinguishing bacterial from viral or allergic conjunctivitis can be challenging.

Microbiological studies

• Smears and cultures of conjunctival and corneal scrapings help identify the causative organism and guide antibiotic therapy
• Gram stain, Giemsa stain, and PCR are useful for detecting specific pathogens like Neisseria or Chlamydia
• Antibiotic susceptibility testing is vital, especially in recurrent or non-responding cases⁸

Treatment

General principles

Empirical treatment should begin promptly, particularly in moderate-to-severe cases, to prevent complications. Therapy can be adjusted based on culture and sensitivity results.

Topical antibiotics

Topical antibiotics are the main method of treatment.

Fluoroquinolones

Fourth-generation agents such as moxifloxacin and gatifloxacin offer broad-spectrum coverage, good corneal penetration, and are effective against Gram-positive and Gram-negative bacteria, including P. aeruginosa.⁹

Aminoglycosides

Tobramycin and gentamicin are effective against Gram-negative organisms, particularly Pseudomonas, but less so against Gram-positive cocci. They are often used in fortified preparations for severe keratitis.¹⁰

Polymyxin B combinations

Polymyxin B-trimethoprim and polymyxin B-bacitracin combinations are effective against a wide spectrum of organisms and are often used in mild-to-moderate conjunctivitis.¹¹

Chloramphenicol

Chloramphenicol remains a cost-effective treatment in some settings and is particularly effective against Streptococcus and Haemophilus species.¹²

Systemic antibiotics

Systemic therapy is indicated for:

• Neisseria gonorrhoeae (e.g., ceftriaxone 1 g IM)
• Chlamydia trachomatis (e.g., azithromycin 1 g orally or doxycycline 100 mg BID for 7 days)
• Severe or systemic infections

Adjunctive therapy

• Lubricating eye drops to reduce discomfort
• Cycloplegics for pain relief in corneal involvement
• Corticosteroids are generally avoided in bacterial infections unless inflammation threatens vision and only under specialist guidance¹³

Antimicrobial resistance

Bacteria can grow resistant to antibiotics. Resistance patterns are evolving, with increasing reports of fluoroquinolone-resistant S. aureus and MRSA strains.¹⁴ Empirical treatment must consider local antibiograms, and culture-based adjustment is recommended for non-responsive infections.

Complications

If not treated adequately, bacterial keratoconjunctivitis can result in:

• Corneal ulceration
• Perforation
• Endophthalmitis
• Scarring and vision loss

Prompt diagnosis, targeted treatment, and patient compliance are crucial to minimise morbidity.

Prevention

• Hand hygiene and environmental sanitation are critical
• Avoidance of shared personal items, such as towels and cosmetics
• Proper contact lens hygiene
• Sexual health education to reduce STI-related keratoconjunctivitis

Conclusion

Bacterial keratoconjunctivitis is a potentially sight-threatening condition requiring prompt diagnosis and treatment. Common pathogens include S. aureus, P. aeruginosa, S. pneumoniae, and H. influenzae, among others. Empirical topical antibiotic therapy should be initiated early and adjusted based on microbiological findings. With growing concerns about antibiotic resistance, tailored treatment strategies and prevention remain essential in clinical practice.