Endophthalmitis after open globe injuries: changes in microbiological spectrum and isolate susceptibility patterns over 14 years

Open globe injuries (OGI) are a common cause of infectious endophthalmitis. The incidence of endophthalmitis in this setting varies from 3% to 48% in various studies, depending on a variety of factors which include setting of trauma, delay of repair, retained intraocular foreign body, and involvement of the crystalline lens [1]. Post-traumatic endophthalmitis is either a community-acquired infection from the unsterile material causing trauma or caused by the inoculation of the normal ocular flora at the time of injury. The purpose of the study is to describe the microbial spectrum and antimicrobial susceptibility in cases of endophthalmitis after OGI and to compare the results with the earlier published data from the same center [2].

This was a retrospective, non-comparative, consecutive case series. Microbiology records were reviewed of all the culture-proven endophthalmitis cases after OGI treated at L. V. Prasad Eye Institute, Hyderabad, India, between January 2006 and March 2013. Bacterial isolates were identified using Analytical Profile Index (API, Bio Meriux, France). The isolate susceptibility to various antimicrobials was determined by the Kirby-Bauer disk diffusion method. Susceptibilities for fungal isolates were not performed. The study was approved by the Institutional Review Board of L. V. Prasad Eye Institute and adhered to the guidelines of the Declaration of Helsinki.

A total of 620 isolates from 581 samples were identified. A total of 38 samples (6.5%) had polymicrobial infection; 37 samples grew two isolates, and one sample grew three organisms. The isolates included gram-positive cocci (296, 47.7%), gram-positive bacilli (117, 18.8%), gram-negative bacteria (142, 22.9%), fungi (55, 8.87%), and Corynebacterium (10, 1.61%) (Table 1).

The most common organism isolated was Bacillus spp. (106/620, 17.1%) followed by Streptococcus pneumoniae (105/620, 16.9%) and coagulase-negative Staphylococci (97/620, 15.6%). Enterobacter was the most common gram-negative isolate (25 of 142 gram-negative isolates). Aspergillus spp. was the most common fungus (20 of 55 fungal isolates) (Table 1).

The spectrum of the isolates identified in this series was similar to that reported in 1999 from the same center [2], with coagulase-negative Staphylococci (CoNS), Streptococcus, and Bacilllus sp. being the three most common organisms (Table 1). The only differences in the spectrum of organisms were the relatively lower incidence of fungal endophthalmitis in the current study (current 8.9% vs earlier 14.4%) and higher incidence of gram-negative isolates (current 25% vs earlier 18%). But, both of these were not statistically significant (p = 0.257 and 0.058, respectively).

Both gram-positive cocci and gram-positive bacilli were generally susceptible to vancomycin (98.2% and 95.6%, respectively). Bacillus sp. was also susceptible to vancomycin (95.1%) as well as to gentamicin (99.1%), amikacin (98.1%), chloramphenicol (92.4%), ciprofloxacin (95.2%), ofloxacin (100%), gatifloxacin (99.1%), and moxifloxacin (97.9%) but its susceptibility to ceftazidime was very poor (11.9%). Gram-negative bacteria were generally susceptible to gatifloxacin (92.9%) followed by ofloxacin (89.4%), chloramphenicol (88.6%), ciprofloxacin (86.6%), amikacin (83.5%), and ceftazidime (77.2%). Among the fluoroquinolones, both gram-positive and gram-negative organisms were most susceptible to gatifloxacin (92.7% and 92.9%, respectively). The antimicrobial susceptibilities of the various isolates are detailed in the Table 1.

The susceptibility of gram-positive organisms continues to be highest to vancomycin. Susceptibility of CoNS to ciprofloxacin had reduced from 100% in 1999 report [2] to 77.3% in the current report (p = 0.007). Similar fluoroquinolone susceptibility trend towards CoNS was noted in the report by Schimel et al. [3]. Susceptibility of gram-negative organisms has slightly decreased over the last two decades. In the 1999 report, gram-negative organisms were 100% susceptible to ciprofloxacin and 95% to amikacin [2]. This has now reduced to 86.6% and 83.5%, respectively, but this change was statistically not significant (p = 0.078 and p = 0.206, respectively). The susceptibility of gram-negative isolates to ceftazidime has increased from 66.7% in 1999 [2] to 77.2% in the current study, and this difference is also not significant (p > 0.05).

The current study indicates that the microbiological spectrum in post-traumatic endophthalmitis has remained the same over the last two decades. Intravitreal vancomycin remains the drug of choice for empiric coverage of gram-positive bacteria. Susceptibility of gram-negative bacteria to commonly used antimicrobials including amikacin and ciprofloxacin has decreased by 10% to 15% and to ceftazidime has increased by 10.5% as compared to the past two decades though statistically not significant. Thus, intravitreal amikacin can be used for empiric coverage of gram-negative bacteria. Ofloxacin is a good option as a systemic antibiotic for broad-spectrum empiric coverage. Also, we report a high prevalence of Bacillus endophthalmitis in open globe injuries that are known to be highly virulent with rapid progression to panophthalmitis [4]. Similar high prevalence of Bacillus endophthalmitis following open globe injuries has been reported in the literature [5, 6].

The microbiological spectrum remains similar over the past 14 years. The susceptibility of gram-negative organisms to commonly used antibiotics has decreased over the time period. Empiric treatment of post-traumatic endophthalmitis with broad-spectrum, combination antibiotics based on the susceptibility pattern in that region is very important for successful anatomical and visual outcomes.