Antibiotic supplementation of intraocular irrigating solutions. An in vitro model of antibacterial action.
OBJECTIVE
The addition of antibiotics to infusion solutions for cataract surgery is becoming increasingly popular. The authors developed an in vitro model to evaluate antibacterial effects of this use of antibiotics.


METHODS
Clinical isolates and/or reference strains of the following organisms were examined: coagulase-negative Staphylococcus spp, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus viridans, Streptococcus spp, Enterococcus spp, Proprionibacterium acnes, Moraxella nonliquifaciens, and Pseudomonas aeruginosa. Standardized suspensions of each organism were incubated with a control solution (Balanced Salt Solution) or Balanced Salt Solution containing the following antibiotics: vancomycin (20 micrograms/ml) or gentamicin (8 micrograms/ml) or gentamicin and vancomycin combined (8 and 20 micrograms/ml, respectively). Suspensions were incubated for 30, 60, and 120 minutes at room temperature. Samples were centrifuged, and the organisms were washed with Balanced Salt Solution before quantitative culturing. Each organism also was incubated for 48 hours in Mueller-Hinton broth with the same antibiotic concentrations.


RESULTS
Most of the organisms were not affected by exposure to the antibiotics for up to 140 minutes. P. aeruginosa and M. nonliquifaciens were exceptions, decreasing in colony numbers even with 30 minutes of exposure. Several Staphylococcus spp yielded variable results. All organisms demonstrated nearly complete inhibition of growth when exposed for an extended time to the appropriate antibiotic in broth.


CONCLUSIONS
Exposure to antibiotics for a short period of time, such as during intraocular surgery, generally has no effect on organisms commonly responsible for endophthalmitis. The use of antibiotics in this manner should be critically reassessed until further study.
Gritz
D C
DC
F. I. Proctor Foundation for Research in Ophthalmology, San Francisco, USA.
Cevallos
A V
AV
Smolin
G
G
Whitcher
J P
JP
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004338:Drug Combinations; D005839:Gentamicins / Q000494:pharmacology*; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D066298:In Vitro Techniques; D007552:Isotonic Solutions; D008826:Microbial Sensitivity Tests / Q000379:methods; D009883:Ophthalmic Solutions; D007507:Therapeutic Irrigation; D014640:Vancomycin / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D004338:Drug Combinations; D005839:Gentamicins; D007552:Isotonic Solutions; D009883:Ophthalmic Solutions; D014640:Vancomycin