HARVARD DEPARTMENT OF OPHTHALMOLOGY
Category : Basic and Translational Research Candidate : Camille Andre Poster #: B3
Characterization of the Resistome in Gram-Positive Bacteria Causing Keratitis
Camille André , Michael S . Gilmore , Paulo J . M . Bispo
Purpose : Antimicrobial resistance ( AMR ) in microbial keratitis is a concerning issue that can result in treatment failure and poor visual outcome . The aim of this study was to characterize phenotypically and genomically the AMR patterns of gram-positive bacteria ( GPB ) isolated from keratitis at Massachusetts Eye and Ear from 2014 to 2017 .
Methods : Whole Genome Sequencing was performed on 161 GPB keratitis isolates using Illumina HiSeq . Molecular typing was performed by MLST . CARD algorithm was used to identify genes and mutations that confer AMR . Minimum inhibitory concentrations were determined by broth microdilution .
Results : Staphylococcus aureus was the most common pathogen ( 53.4 %) and its population structure was dominated by lineages grouped within the clonal complex 5 ( 32.6 %), which includes epidemic MRSA strains commonly associated with multidrug-resistant ( MDR ) infections . Compared with methicillin-susceptible S . aureus , resistance to other antibiotics was more prevalent among MRSA isolates , with rates of resistance higher than 70 % for fluoroquinolones ( FQ ) and azithromycin . The newest FQ ( besifloxacin and moxifloxacin ) had lower MIC90 compared with the earlier ones . More than 30 % of coagulase-negative Staphylococcus were resistant to FQ and half of them were resistant to azithromycin ( 52.9 %). We found between 2 and 4 mutations in the quinolone resistance-determining regions ( QRDR ) of gyrA and parC genes for staphylococci isolates ( 21.7 % of S . epidermidis and 25.0 % of S . aureus ) that were associated with high FQ MICs . 52.1 % of S . epidermidis and 22.1 % of S . aureus were MDR . CARD analysis revealed that 26.7 % of S . aureus co-harbored ant ( 9 ) -Ia and ermA genes that confer resistance to aminoglycosides , and to macrolides , lincosamides and streptogramin B , localized in a Tn554 transposon , whereas macrolide resistance in S . epidermidis was frequently associated with a mphC / msrA genotype . S . epidermidis were also positive for the dfrC ( 82.6 %) and tetK genes ( 21.7 %) which confers resistance to diaminopyrimidine and tetracycline respectively . Among S . pneumoniae isolates , resistance rates were less than 10 % to all antibiotics tested except for ofloxacin ( 14.4 %), azithromycin ( 30.8 %) and penicillin ( 30.8 %). These isolates often carried macrolide resistance genes ( ermB and mefA / msrD ) that are integrated into mobile genetic elements .
Conclusions : We provided an overview of current rates of resistance to antibiotics commonly used to treat keratitis caused by GPB and a characterization of the diversity of the associated molecular mechanisms that confer AMR .