June 2022
Volume 63, Issue 7
Open Access
ARVO Annual Meeting Abstract  |   June 2022
Characterization of the resistome in gram-positive bacteria causing keratitis
Author Affiliations & Notes
  • Camille Andre
    Massachusetts Eye and Ear Department of Ophthalmology, Boston, Massachusetts, United States
    Harvard Medical School Department of Ophthalmology, Boston, Massachusetts, United States
  • Michael Gilmore
    Massachusetts Eye and Ear Department of Ophthalmology, Boston, Massachusetts, United States
    Harvard Medical School Department of Microbiology and Immunobiology, Boston, Massachusetts, United States
  • Paulo J.M. Bispo
    Massachusetts Eye and Ear Department of Ophthalmology, Boston, Massachusetts, United States
    Harvard Medical School Department of Ophthalmology, Boston, Massachusetts, United States
  • Footnotes
    Commercial Relationships   Camille Andre None; Michael Gilmore None; Paulo Bispo None
  • Footnotes
    Support  Fondation pour la Recherche Médicale FDM202006011203
Investigative Ophthalmology & Visual Science June 2022, Vol.63, 3555 – A0442. doi:
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    • Get Citation

      Camille Andre, Michael Gilmore, Paulo J.M. Bispo; Characterization of the resistome in gram-positive bacteria causing keratitis. Invest. Ophthalmol. Vis. Sci. 2022;63(7):3555 – A0442.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

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 overall 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). 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 confers 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 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%).

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 antimicrobial resistance.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

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