Genotypic and Phenotypic Antibiotic Resistance in Staphylococcus Epidermidis Endophthalmitis

To evaluate antibiotic resistance patterns in Staphylococcus epidermis endophthalmitis isolates, identify antibiotic resistance genes, and compare this to their phenotypic resistance.

Retrospective case series of S. epidermidis isolates from January 2012 to December 2017. Phenotypic resistance was determined from minimum inhibitory concentration values. Genotypic resistance was determined from DNA microarray. The relationship between these was analyzed using Cohen's kappa and predictive value.

Seventy-five isolates were included. More than 60% were resistant to methicillin and erythromycin. Approximately 60% possessed the resistance genes for methicillin and erythromycin, and 25% for clindamycin. There was near perfect agreement between genotype and phenotype for erythromycin and methicillin (kappa = 0.88 and 0.89, respectively). Approximately 98% (P < 0.0001) of isolates with erythromycin and methicillin resistance genes and 90% (P = 0.0006) with clindamycin resistance genes were phenotypically resistant to those antibiotics. None were resistant to vancomycin.

The relationship between genotypic and phenotypic antibiotic resistance highlights that resistance may be polygenic, and genes may be silent. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:S13-S16.].