Staphylococcal ocular isolate resistance to broad spectrum antibiotics: a temporal study

Purpose. Staphylococcus is a commonly encountered ocular pathogen. This study investigates resistance patterns of ocular isolates of coagulase positive and coagulase negative Staphylococcus to the broad spectrum antibiotics: gentamicin and erythromycin. Methods. The culture and sensitivity results of all ocular isolates of Staphylococcus for the period of June 1, 1985 to June 30, 1996 were obtained from the microbiology department records of Stanford University Medical Center. All specimens which were tested for sensitivity to erythromycin and/or gentamicin were included. The proportion of specimens sensitive to erythromycin and gentamicin were determined. These results were compared to all Staphylococcal isolates collected during the time period September 1, 1976 to July 31, 1980. Results. Sensitivity testing of 1240 Staph. cultures to erythromycin was done. Sensitivity to erythromycin decreased from 87% (N=773) in the time period 1976 to 1980 to 50% (N=121) in the time period 1985 to 1996 in coagulase negative S. species (P<. 001). Similarly, sensitivity to erythromycin decreased from 98% (N=42) to 78% (N=304) in 5. aureus (P<. 005). Sensitivity testing of 1269 Staph. cultures to gentamicin was done. Sensitivity to gentamicin decreased from 100% (N=773) in the time period 1976 to 1980 to 78% (N=147) in the time period 1985 to 1996 in coagulase negative S. species (P<. 001). There was a trend of decreasing sensitivity from 100% (N=42) to 98% (N=307) in S. aureus, which was not statistically significant, in the same time period. Sensitivity to gentamicin decreased from 100% (N=815) to 91% (N=454) in S. aureus and coagulase negative S. species combined (P<. 001). Conclusion. Greater resistance to both erythromycin and gentamicin was demonstrated in both coagulase positive and coagulase negative Staphylococcus during the 1985 to 1996 time period relative to the 1976 to 1980 period.