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Diana Laura, Nathan L. Scott, Kenneth C. Fan, Darlene Miller, Harry Flynn; Genotypic and phenotypic antibiotic resistance in Staphylococcus epidermis endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3257.
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© ARVO (1962-2015); The Authors (2016-present)
Endophthalmitis generally requires treatment with multiple antibiotic agents, and reports indicate there has been an increase in the amount of antimicrobial resistance worldwide. This study aims to identify antibiotic resistance genes in Staphylococcus epidermis (S. epidermis) endophthalmitis isolates, and compare this to their phenotypic resistance.
Retrospective study of eyes with S. epidermis endophthalmitis. Culture results were gathered, along with antibiotic susceptibility profiles identified using standard microbiologic protocols (i.e. phenotypic resistance). DNA microarray survey of antibiotic resistance genes (i.e. genotypic resistance) for methicillin, clindamycin, erythromycin, gentamycin, and vancomycin in these isolates were obtained. Agreement between the two variables was assessed using McNemar tests.
Seventy-five S. epidermis isolates were included: 24 from right eye (OD) vitreous samples, 29 from left eye (OS) vitreous samples, 5 OD anterior chamber tap, 6 OS anterior chamber tap, 6 OS vitreous wash, 4 OD vitreous wash, and 1 OS intraocular lens culture. Forty-seven (63%) were resistant to methicillin, 29 (39%) to clindamycin, 49 (65%) to erythromycin, 3 (4%) to gentamycin, and none to vancomycin. DNA microarray results disclosed 45 (60%) possessed the gene for methicillin resistance, 18 (24%) for clindamycin resistance, 2 (3%) for erythromycin resistance, 9 (12%) for gentamycin resistance, and none for vancomycin resistance. McNemar testing disclosed near perfect agreement between genotypic and phenotypic resistance to methicillin (κ=0.89, p=0.63). For clindamycin, kappa indicated a substantial agreement (κ =0.61) but still a statistically significant amount of disagreement (p=0.003) between the 2 variables. There was a statistically significant disagreement between the 2 variables for erythromycin (κ=0.02, p<0.0001) and gentamycin (κ=0.47, p=0.03). For vancomycin, there was perfect agreement in the 2 variables.
We found differences in phenotypic resistance and genotypic resistance to clindamycin, erythromycin and gentamycin in S. epidermis endophthalmitis isolates, while agreement of these variables existed for methicillin and vancomycin. This may indicate that some resistance genes are not expressed or that resistance patterns may be polygenic, and not all resistance genes have been identified.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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