Bacterial keratitis: a prospective clinical and microbiological study

Abstract

Aim: To define the clinical and microbiological profile of bacterial keratitis at the Jules Gonin Eye Hospital and to test the in vitro bacterial resistance.

Methods: Patients presenting with bacterial keratitis were prospectively followed; clinical features (age, risk factors, visual acuity) and response to therapy were analysed. Bacteriological profile was determined and the sensitivity/resistance of isolated strains were tested towards 12 ocular antibiotics (NCCLS disc diffusion test).

Results: 85 consecutive patients (mean age 44.3 (SD 20.7) years) were prospectively enrolled from 1 March 1997 to 30 November 1998. The following risk factors were identified: contact lens wear, 36%; blepharitis, 21%; trauma, 20%; xerophthalmia, 15%; keratopathies, 8%; and eyelid abnormalities, 6%. The most commonly isolated bacteria were Staphylococcus epidermidis, 40%; Staphylococcus aureus, 22%; Streptococcus pneumoniae, 8%; others Streptococcus species, 5%; Pseudomonas, 9%; Moraxella and Serratia marcescens, 5% each; Bacillus, Corynebacterium, Alcaligenes xyloxidans, Morganella morganii, and Haemophilus influenza, 1% each. 1-15% of strains were resistant to fluoroquinolones, 13-22% to aminoglycosides, 37% to cefazolin, 18% to chloramphenicol, 54% to polymyxin B, 51% to fusidic acid, and 45% to bacitracin. Five of the 85 patients (5.8%) had a poor clinical outcome with a visual loss of one or more lines of visual acuity.

Conclusion: Fluoroquinolones appear to be the therapy of choice for bacterial keratitis, but, based upon these in vitro studies, some strains may be resistant.

Figure 1

Contact lens wear is by far the most common risk factor encountered. The numbers refer to the numbers of patients. Blepharitis and trauma are also major risk factors for the development of keratitis. Other aetiologies, such as dry eye syndrome, keratopathies, and eyelid pathologies, are less common risk factors.

Figure 2

Gram positive bacteria are by far the most commonly isolated organisms of which Staphylococcus species predominate. Pseudomonas aeruginosa is the Gram negative bacterium most encountered.

Figure 3

Chloramphenicol, cefazolin, and new fluoroquinolones (particularly ofloxacin) are very effective against Gram positive bacteria. In contrast, many of these same bacteria are resistant to polymyxin B (A). Similar to the effectiveness against Gram positive bacteria, the new fluoroquinolones are also effective against Gram negative bacteria. Aminoglycosides (tobramycin, neomycin, and gentamicin) also provide a broad spectrum of activity against Gram negative pathogens. Bacitracin, cefazolin, chloramphenicol, and fusidic acid, on the contrary, have little effect against these bacteria (B).

Figure 3

Chloramphenicol, cefazolin, and new fluoroquinolones (particularly ofloxacin) are very effective against Gram positive bacteria. In contrast, many of these same bacteria are resistant to polymyxin B (A). Similar to the effectiveness against Gram positive bacteria, the new fluoroquinolones are also effective against Gram negative bacteria. Aminoglycosides (tobramycin, neomycin, and gentamicin) also provide a broad spectrum of activity against Gram negative pathogens. Bacitracin, cefazolin, chloramphenicol, and fusidic acid, on the contrary, have little effect against these bacteria (B).