Cornea epithelial cells secrete IgA or surfactant proteins, e.g., surfactant protein, mucin glycoproteins, tight-junction/epithelial polarity, and epithelium-derived antimicrobial peptides (AMPs), which can inhibit or kill microbes. Unlike general infections, most ocular infections caused by S. maltophilia are preceded by ocular instability such as trauma and the use of contact lenses . The barrier of corneal epithelial cells is destroyed, creating conditions that facilitate bacterial infection. Wiley et al. reported that S. maltophilia is one of the dominant bacteria of biofilms detected on patients’ contact lenses and is resistant to lens cleansers. In addition, the simultaneous use of corticosteroids in patients with corneal defects increases the risk of infection . Another cause of S. maltophilia keratitis is ocular surface defects resulting from previous corneal surgeries or a patient’s corneal disease. It has been reported that patients with S. maltophilia keratitis have a higher incidence of ocular surface disease than those with other types of bacteria-induced keratitis [18, 19]. Similar to those reported previously, in the present study, the predominant causes in most cases were ocular trauma and the use of contact lenses. HSV keratitis and exposure keratitis, which can cause instability of the ocular surface, were also noted.
Infections due to S. maltophilia are less common than those due to Pseudomonas aeruginosa and have less toxic characteristics. Increased resistance of S. maltophilia to aminoglycosides, fluoroquinolones, and most beta-lactam antibiotics leads to poor treatment outcomes and is clinically important. A recent study showed that S. maltophilia is susceptible to the mixed use of ticarcillin and clavulanic acid . It has been reported that S. maltophilia shows multidrug resistance to commonly used antibiotics and carbapenems [7, 8]; however, fluoroquinolone antibiotics may be the treatment of choice, based on a study by An-Lun et al. . Another study has also shown that fluoroquinolones are also effective against S. maltophilia-associated endophthalmitis . In the present study, most patients were susceptible to fluoroquinolones, beta-lactams, and aminoglycosides, except three patients who were resistant to multiple drugs. We compared the efficacy of antibiotics between the two groups. Visual acuities after treatment were significantly higher in the group using mixed fluoroquinolone, beta lactam, and aminoglycoside. Moreover, in the group using mixed beta lactams and aminoglycosides, two of eight patients did not show better outcomes than their initial visual acuities, and one patient underwent evisceration.
Multi-pathogenic infections in patients with S. maltophilia-associated ocular infection show poorer results than mono-pathogenic infections . According to a previous study, the indirect pathogenicity of S. maltophilia plays an important role in the intervention between species . In the present study, three cases had polymicrobial infections; two of these patients were classified as multidrug resistant, and one of them had culture-proven P. aeruginosa infection that did not respond to treatment. Eventually, this patient underwent evisceration. Accordingly, the results seem to be similar to those of other studies.
The limitations of this study were its retrospective design, involving a single center, and the small sample size. More accurate information regarding the response of S. maltophilia to antibiotics and treatment for polymicrobial infections requires extensive prospective research. Briefly, S. maltophilia is a relatively uncommon pathogen of keratitis, and S. maltophilia keratitis is related to several risk factors that cause instability of the ocular surface. Mixed use of fluoroquinolones, beta-lactams, and aminoglycosides is the treatment of choice for S. maltophilia infectious keratitis. In addition, in cases of polymicrobial infections, clinical attention is required because of resistance to antibiotics and poor outcomes.