Preoperative microbiologic diagnosis before elective intraocular interventions and prevention of infection with tobramycin eyedrops. Results of a multicenter study

Preoperative conjunctival smears of 313 asymptomatic patients before cataract surgery were evaluated in an open multi-center study in 10 German surgical eye care centers from May to August 1987. 230 evaluable isolates of 198 patients (= 61.1%) on agar plates with a 48 h incubation period revealed 190 gram-positive (most frequent isolates: 62.2% coagulase negative Staph., 13.5% coagulase positive Staph.) and 40 gram negative agents (most frequent isolates: 3.0% Proteus sp., 2.2% Pseudomonas sp.). Coinfections with gram-positive organisms were seen in 22%, and with gram-negative organisms in 9% of cases. Newly acquired potentially pathogenic bacteria were demonstrated after one day (5-8 drops 3 mg/ml Tobramycin (Tobramaxin; 1 x ointment in the evening 3 mg/100 mg Tobramycin (Tobramaxin] of topical prophylaxis in 6 of 115 (= 5.2%) previously negative and 22 of 198 (= 11%) previously positive conjunctival cultures. Coagulase negative Tobramycin sensitive Staph. persisted in 41 of 110 patients (= 37.3%) and coagulase positive Tobramycin-sensitive Staph. in 4 of 30 (= 13.3%). Each of the gram-negative bacteria could be eliminated after one day of topical prophylaxis with Tobramycin eye drops and ointment in this study. The statistically determined elimination rate estimated for a one-day topical prophylaxis with Tobramycin in asymptomatic culture-positive persons was 77.5-89.8% (95% confidence interval/Pearson and Clopper). The statistically determined probability for potentially pathogenic bacteria in a previously culture-negative patient after topical preoperative Tobramycin prophylaxis was 3.1-13.2% (95% confidence interval/Pearson and Clopper). Thus, additional supportive antibiotic measures are to be taken pre- and perioperatively by the intraocular surgeon to minimize the risk of postoperative endophthalmitis.