Characterization and Correlation of Staphylococcus aureus Virulence Factors ARG and Spa Profiles with Site Specific Ocular Infections

Abstract

Purpose : Staphylococcus aureus is a common ocular infection. Severity is determined by strain, ocular site, and host response. We explored the relationship between methicillin susceptibility profiles, arg groups, and Spa types among keratitis, endophthalmitis, conjunctivitis isolates.

Methods : A combination of molecular and routine microbiology tests were used to characterize 112 isolates from the conjunctiva (n=72), cornea (n=28), and intraocular fluids (e.g. anterior chamber, vitreous fluids) (n=12).

Results : Forty-four known spa types were detected in the isolates. The most frequent spa types were t002 (n=15), t008 (n=14), t064 (n=5), and t012 (n=4). Twelve samples (10.7%) detected new spa types not found in the database. Samples containing these new spa types were found in the cornea 58.3% (n=7) and conjunctiva 41.7% (n=5). Spa diversity varied by ocular site: conjunctiva (n=32/44, ), cornea (n=14/44), and intraocular fluids (n=11/44). Spa types that were the same among the cornea and conjunctiva samples were t002, t045, t064, t571, and t1451. At the same frequency, five spa types were shared among conjunctiva and intraocular fluids: t008, t012, t306, t1451, and t3841. Spa type t1451 was the only spa type found in all three of the ocular sources.

The diversity of spa isolates was greater in MSSA isolates, 72.7% (n=32/44), as compared to MRSA isolates, 43.2% (n=19/44). 15.9% (n=7/44) of the spa types detected in the isolates were found in both MRSA and MSSA isolates. Of the MRSA isolates, SCCmec types II (typically hospital-acquired) had greater spa diversity (n=9) as compared to type IV (typically community-acquired) (n=6).

Isolates with spa t002 (n=15) were all Arg2 and PVL-. All of the MRSA isolates containing spa t002 (n=11) were also exclusively SCCmec type II (usually hospital-acquired). Isolates with spa t008 (n=14) were all Arg1, PVL+. Most of the spa t008 MRSA isolates (n=8/11) were SCCmec type IV (typically hospital-acquired).

Conclusions : A diversity of known and emerging spa types were detected among ocular samples from the ocular surface and intraocular fluids. Agr groups (I, II) associated with invasive and healthcare infections are common among this group. This combination of virulence factors contributes to the severity and morbidity of ocular S. aureus isolates.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.