Pseudomonas keratitis

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 by Augustine Hong, MD on October 12, 2020.


Disease Entity

Disease

Pseudomonas aeruginosa is a gram-negative rod. It is an opportunistic human pathogen, known to cause a variety of infectious diseases. In the eye, P. aeruginosa is a common cause of bacterial keratitis, particularly in contact lens wearers. It is known to be particularly virulent, with pseudomonas keratitis being more difficult to treat and have worse prognosis than other forms of bacterial keratitis. P. aeruginosa secretes proteases that can cause liquefactive necrosis of the cornea, leading to rapid corneal weakening and perforation.

Epidemiology

Pseudomonas is the leading cause of gram-negative bacterial keratitis, and one of the most common causes of bacterial keratitis overall. In one meta-analysis, prevalence of P. aeruginosa isolates in bacterial keratitis ranged from 6.8 to 55%[1].

It is widely known that pseudomonas keratitis is strongly associated with contact lens wear. In one study, incidence of pseudomonas keratitis was 2.76 cases per 10000 individuals per year, but rose to 13.04 cases per 10000 individuals when only considering contact lens wearers[2]. In the same study, 55% of cases of pseudomonas keratitis were associated with contact lens wear.

Extended contact lens use allows adhesion of P. aeruginosa to contact lens surfaces and subsequently the cornea. P. aeruginosa possesses specific virulence factors, including pili, glycocalyx, and exotoxins, which allow adherence and invasion into the cornea[3].

Diagnosis and treatment

All cases of suspected pseudomonas keratitis should be scraped and cultured. Treatment for pseudomonas keratitis is generally monotherapy with a fluoroquinolone eyedrop such as ciprofloxacin or moxifloxacin. Studies have shown fluoroquinolone monotherapy is non-inferior and has fewer side effects compared to combined tobramycin-cefazolin[4]. Other choices include fortified aminoglycosides such as tobramycin.

Steroid use in conjunction with antibiotics is controversial in the setting of pseudomonas keratitis as well as microbial keratitis as a whole. On subgroup analysis on patients from the steroids for corneal ulcers trial (SCUT), showed that pseudomonas ulcers had no overall benefit with the addition of corticosteroids[5]. However, the same study showed that the invasive subtype of P. aeruginosa may demonstrate a small improvement in visual acuity with steroids versus placebo.

References

  1. Teweldemedhin M, Gebreyesus H, Atsbaha AH, Asgedom SW, Saravanan M. Bacterial profile of ocular infections: a systematic review. BMC Ophthalmol. 2017;17(1):212. Published 2017 Nov 25.
  2. Jeng BH, Gritz DC.Epidemiology of ulcerative keratitis in northern California. Arch Ophthalmol. 2010 Aug;128(8):1022-8.    
  3. Dart JKG , Seal DV. Pathogenesis and Therapy of Pseudomonas aeruglnosa Keratitis. Eye (1988) 2, Suppl S46-S55
  4. O'Brien TP, Maguire MG, Fink NE, Alfonso E, McDonnell. Efficacy of ofloxacin vs cefazolin and tobramycin in the therapy for bacterial keratitis. Report from the Bacterial Keratitis Study Research Group. P Arch Ophthalmol. 1995 Oct; 113(10):1257-65.
  5. Borkar DS, Fleiszig SM, Leong C, et al. Association between cytotoxic and invasive Pseudomonas aeruginosa and clinical outcomes in bacterial keratitis. JAMA Ophthalmol. 2013;131(2):147–153.