Bacteria associated with intravitreal injection appear susceptible to newer antibiotics

The first prospective study to characterize antibiotic susceptibility patterns of bacteria isolated from intravitreal injection sites has found that conjunctival flora has grown resistant to commercially available penicillin analogues and fluoroquinolones, but most are sensitive to newer fluoroquinolones.

Researchers isolated bacteria from the injection site of 85 patients (90 eyes) patients undergoing intravitreal injection. Of the 71 species isolated, 83 percent were coagulase-negative staphylococcus (CNS). Half of the CNS were oxacillin resistant and 34 percent were multiresistant to five or more of the 14 antibiotics tested.

However, most CNS remained sensitive to cefazolin, cefotaxime/ceftriaxone, gentamicin, imipenem, moxifloxacin, gatifloxacin, chloramphenicol, and tetracycline. None were found to be vancomycin resistant. Of the commercially available topical antibiotics tested, gentamicin and the newer generation fluoroquinolones, gatifloxacin and moxifloxacin, provided the best coverage for all species cultured.

The authors note several limitations of their study. They did not evaluate the need for antibiotics in the peri-injection period. They say clinicians should carefully weigh the merits and disadvantages of using such agents. There was also the potential of a selection bias toward faster-growing organisms due to the five-day sample incubation period, leading to a possible underrepresentation of slower growing, facultative organisms. Lastly, the small number of non-CNS organisms isolated prohibited the authors from drawing clinically significant conclusions about non-CNS isolate susceptibility profiles.

The authors conclude that these results underscore the critical role of prophylactic antibiotics in preventing postinjection endophthalmitis.