is a rare source of ocular infection. The first reported case of S. maltophilia
endophthalmitis was in 1989 after implantation of a ganciclovir implant in a patient with acquired immune deficiency syndrome.24
This patient eventually required pars plana vitrectomy and removal of the implant, along with intravitreal and systemic antibiotic therapy. The overall frequency of S. maltophilia
as a causative organism for endophthalmitis is not well documented. In the Endophthalmitis Vitrectomy Study, Gram-negative organisms accounted for 6.1% of cases.32
In 2008, Lalwani et al reported 9.6% cases of endophthalmitis in a review of 73 post-surgical endophthalmitis cases treated at BPEI.33
Horster et al reported an outbreak of S. maltophilia
endophthalmitis in a series of 26 patients following cataract surgery.22
In this series, all patients had surgery within two days at the same hospital. The irrigation solution was found to be the source of the pathogen. Favorable visual outcomes were achieved, and all patients were treated promptly with intravitreal antibiotics and pars plana vitrectomy. The strains were confirmed by restriction fragment length polymorphism and pulsed field gel electrophoresis typing. This rapid diagnosis and treatment differs from our cases, where six of our eight cases presented after ten postoperative days or more. In cases 1 and 5, the inflammatory response and infection occurred within one week. Cases 4, 6, and 7 occurred within approximately 1–3 weeks after surgery, and cases 2 and 3 were reported more than one month after surgery. In case 2, more than 100 days had elapsed before definitive therapy was given. This suggests that, in some cases, the organism is less virulent than other organisms implicated in endophthalmitis, and may be responsible for acute or chronic endophthalmitis. No other unique clinical features were identified in this case review. Other reports of postoperative S. maltophilia
endophthalmitis have contained few patients or multiple organisms causing endophthalmitis.30
In this study, seven of the seven tested isolates were noted to be sensitive to ceftazidime. Case 8, who did not have ceftazidime sensitivity data, was treated with ceftazidime and improved, although this patient was also treated with oral gatifloxacin. A previous report of endophthalmitis by Chen et al demonstrated a high frequency of S. maltophilia
resistant to ceftazidime.31
Penland et al reported antimicrobial susceptibilities of 15 ocular isolates of S. maltophilia
, and found resistance to ceftazidime in five of 15 isolates.2
The reason for this difference in sensitivities may be related to selective pressure of antibiotic use in differing geographic regions or different time periods of study. Also, the methodology, resistance criteria, and media used for antibiotic sensitivities may have differed. Ceftazidime is often a first-line intravitreal antibiotic agent, chosen because of its wide coverage and low intraocular toxicity. Another common first-line option is amikacin, although fewer isolates (six of eight) were sensitive to amikacin than to ceftazidime in our series.
The series presented in this paper includes seven of eight isolates sensitive to polymyxin B. Two of five tested isolates were sensitive to trimethoprim-sulfamethoxazole, a therapeutic agent commonly used for S. maltophilia
. Three isolates were not tested, and two demonstrated mixed sensitivity or resistance to trimethoprim-sulfamethoxazole. Five of the seven isolates tested were sensitive to ciprofloxacin, and three of three tested isolates were sensitive to levofloxacin. Fluoroquinolones are another common antibiotic class used in the treatment of S. maltophilia
. Susceptibility to tetracyclines was not investigated. Penland et al noted high susceptibility rates to the aminoglycosides (gentamicin and tobramycin), with 12 of 15 isolates sensitive to both agents.2
In our series, none of the eight isolates were sensitive to gentamicin, and five of eight were sensitive to tobramycin.
Inflammation may also play a role in the vision loss as well. Six of the eight patients in this series were treated with intravitreal steroids. The two patients who did not receive intravitreal steroids had the best visual acuity of the group, but the numbers were too low and too many variables were involved in treatment to make any meaningful comparison. The two patients who were not treated with dexamethasone also had the longest time to presentation, which may indicate they had less virulent infection.
Limitations of this study include those of any retrospective review. Because postoperative endophthalmitis has become increasingly rare, and the organism in question is atypical, the number of cases available was small. Antibiotic susceptibilities were measured ex vivo, and may not completely represent the complete in vivo state. In the case of polymyxin B susceptibility testing, there may have been some variation between the disk diffusion and minimum inhibitory concentration methods.
In case 4, three separate vitreous cultures were performed, with differing sensitivity results for ceftazidime. The first culture showed resistance to ceftazidime, the second had intermediate sensitivity, and the third was sensitive. One possibility is that the resistance testing may have had some variability. It is also possible that there was selective pressure after initial injection of antibiotics, causing a change in the resistance profile for the organism.
S. maltophilia is a rare causative organism for endophthalmitis. This study represents a review of several cases treated at an academic referral center following cataract surgery. Visual outcomes demonstrated visual acuity better than 20/150 in the majority of cases. Antibiotic resistance testing showed sensitivity to ceftazidime and amikacin, suggesting that these antibiotics may be useful as intravitreal therapy in the treatment and prevention of this pathogen. Sensitivity to polymyxin B suggests that this agent may be a useful topical antibiotic for prevention.