Unusual case of methicillin resistant staphylococcus aureus and acanthamoeba keratitis in a non-contact lens wearer from Kashmir, India

Abstract

Acanthamoeba species can cause a chronic, progressive, ulcerative keratitis of the eye, which is not responsive to the usual antimicrobial treatment and is frequently mistaken for stromal herpes keratitis. Acanthamoeba keratitis continues to be a burgeoning and unsolved problem. Although soft contact lens wear is reported as the major risk factor in other parts of the world, reports from India suggest that acanthamoeba keratitis is more common among non-contact lens wearers. An unusual case of coinfection with Acanthamoeba and methicillin resistant staphylococcus aureus (MRSA) as causes of corneal keratitis in a contact lens wearer from Kashmir, India, is reported. Recent findings have shown that MRSA uses amoebae to spread, sidestepping hospital and other protection measures. Cysts of the isolated Acanthamoeba tolerated an incubation temperature of 40°C, indicating a pathogenic species. This case highlights the importance of culture methods in the diagnosis of corneal infection and the choice of treatment regimen.

BACKGROUND

Acanthamoeba keratitis has been described as a recent epidemic with soft contact lens wear as the greatest risk factor. With most of the literature focusing on contact lens-related acanthamoeba keratitis, ophthalmologists may hesitate to diagnose this entity in patients without contact lenses, which may eventually lead to significantly delay in diagnosis and hence poor visual outcome in such patients; hence, a high index of suspicion is needed for this disease entity. Patients with treatment-resistant keratitis, even non-contact lens wearers, should be examined for the presence of Acanthamoeba by means of specific cultures, histopathological staining and, if necessary, corneal biopsy, and appropriate treatment should be instituted at the earliest to prevent the progression of the disease process and prevent visual loss.

CASE PRESENTATION

A 40-year-old male was referred to the ophthalmic department of Sheri Kashmir Institute of Medical Sciences, Medical College, India, for non-healing corneal ulcer in the right eye by a private practitioner. The patient had received topical antibiotics and corticosteroids for the last 21 days with no relief of symptoms.

The patient did not recall any history of trauma and gave no history of contact lens wear. The patient complained of severe pain, photophobia and blurring of vision in the right eye. On examination the lids were oedematous, and both conjunctivae were hyperaemic and oedematous (fig 1). His right cornea had a dendritiform ulcer measuring 3.5×6 mm with a surrounding stromal infiltrate. The anterior chamber was hazy with hypopyon. His visual acuity in the right eye was finger counting and left eye was 6/9.

Figure 1.

Conjunctival hyperaemia and corneal ulcer of the right eye with stromal infiltration.

Thinking of a possible microbial aetiology, swabs were taken from the ulcer and subjected to bacterial culture, which showed growth of methicillin resistant staphylococcus aureus (MRSA). The patient was put on subcunjunctival vancomycin and amikacin. Over the next week, the ulcer worsened with increase in size, inflammation and stromal infiltration.

INVESTIGATIONS

Corneal scrapings were taken under local anaesthesia and inoculated onto two plates of Escherichia coli seeded non-nutrient agar plates (ECNNA), which were incubated at 25 and 37°C. A KOH mount and Giemsa staining of the scraping showed polygonal double walled cysts of Acanthamoeba. After 72 hours of incubation the plates seen under the microscope showed trophozoites of Acanthamoeba. Further incubation to 7 days yielded the cyst stage of amoeba, which remained viable at 40°C for several days. These temperature tolerance results indicated that the strain of Acanthamoeba was pathogenic.^1,2

OUTCOME AND FOLLOW-UP

Because of the cost involved and local non-availability of the drugs used for treatment of acanthamoeba keratitis, corneal debridement of the ulcer was done and the patient was put on 0.006% chlorhexadine solution as per recommendation by Kosrirukvongs et al.³ The stromal infiltrates decreased and hypopyon resolved completely. At the last follow up in July 2008, the patient has no sign of corneal inflammation, although his visual acuity did not improve beyond finger counting.

DISCUSSION

Infections of humans with free living amoebas are an infrequent but often life-threatening occurrence in both normal and immunocompromised individuals. Free-living amoebae belonging to the genus Acanthamoeba have been found worldwide in soil, dust, air and water and are relatively resistant to normal level of chlorine in tap water.¹ Recent interest in the Acanthamoeba species has focussed on their causative role in a painful, vision-threatening keratitis that occurs mainly in contact lens users.^4,5 Although disseminated Acanthamoeba infection is increasingly described in immunocompromised host, acanthamoeba keratitis is usually seen in the healthy individual. Martinez et al has to date reported a total of 1350 cases worldwide.⁶ Of the first 100 cases of acanthamoeba keratitis reported to the Centre for Disease Control and Prevention, 83% occurred in people who were contact lens wearers and corneal infection was associated with the use of homemade saline to clean the lenses and wearing the lens while swimming.⁷ In non-contact lens wearers, it is generally accepted that eye infection ensues subsequent to minor corneal trauma with introduction of amoebae from environmental sources.⁸ Because diagnosis is difficult and often delayed, infection with Acanthamoeba may result in total loss of sight in the infected eye. However, if infection is recognised early, wide epithelial debridement may be curative if epithelium alone is involved.⁹ However, a number of therapeutic agents are not effective in the later stages when amoebae invade tissue beneath the cornea¹⁰

Reports of acanthamoeba keratitis are rare in the Indian literature. Inadequate facilities for microbiological investigations in ophthalmic institutions probably are responsible for this lacuna.

In this part of India, where use of contact lens is considered to be a luxury due to generally low socioeconomic status of people, we report an unusual case of MSRA and acanthamoeba keratitis in a non-contact lens wearer.

This report illustrates a case of acanthamoeba keratitis with MRSA in a non contact lens wearer. Suppurative keratitis due to the Acanthamoeba species is commonly associated with contact lens use and as a result of poor lens hygiene.¹¹ However, increasingly these ulcers are being reported in developing countries who have no history of contact lens wear.

Acanthamoeba keratitis should be considered in the differential diagnosis of any chronically progressive ulcerative keratitis and in progressively worsening corneal ulcer that are non-responsive to usual antimicrobial treatment.¹² It is also important to consider the possibility of a coexisting bacterial and Acanthamoeba infection. In our case, we found a co-existing MRSA and Acanthamoeba, which is the first of its kind being reported from Kashmir, India. Osugi et al reported a case of initially MRSA positive acanthamoeba keratitis from Japan.¹³ Recent findings in the University of Bath, UK, demonstrate that MRSA can infect and replicate inside of Acanthamoeba and these pathogens are more resistant to antibiotics and more virulent.¹⁴ The recent microbiologic literature has centred around MRSA non-responding to medications because the bacteria are hiding in Acanthamoeba; thus, promoting persistence of epidemic strains of MRSA.¹⁵

In light of these observations, it is advisable to culture for bacteria and to use appropriate antimicrobials as well. This case serves as an illustration that Acanthamoeba is an emergency and early and accurate detection of infection is important for its proper management.

LEARNING POINTS

• Acanthamoeba keratitis is a rare entity in India.

• The treating ophthalmologist should consider it in the differential diagnosis of any chronic, progressive, non-healing corneal ulcer.

• Coinfection with bacteria like MRSA can be a problem, so appropriate and timely management is needed.

• Pathogenic species of MRSA can replicate within the amoebae giving rise to more virulent and more resistant strains non responsive to treatment.