Staphylococcus aureus isolated from endophthalmitis are hospital-acquired based on Panton-Valentine leukocidin and antibiotic susceptibility testing

Abstract

Purpose: Staphylococcus aureus (SA) endophthalmitis is generally a postsurgical infection with an undefined source of entry. Hospital-acquired (HA) SA infections are associated with multi-antibiotic resistance and absence of the Panton-Valentine Leukocidin (PVL) toxin. Community-acquired (CA) SA infections are not associated with multi-antibiotic resistance and possess the PVL toxin. We hypothesize that CA infection is more common than HA for SA endophthalmitis.

Methods: Twenty de-identified SA isolates, collected from the vitreous and/or aqueous of clinical endophthalmitis, were tested for the presence of PVL toxin and antibiotic susceptibility. PVL testing was performed using a kit to detect the Staphylococcal toxin by reversed passive latex agglutination (PVL-RPLA "Seiken," Denka Seiken Co., LTD). SA isolates were tested for antibiotic susceptibility using disk diffusion at the time of isolation. Multi-antibiotic resistance was defined as resistance to at least 3 classes of antibiotics.

Results: Of the 20 isolates, 15 were multi-antibiotic resistant and PVL-negative consistent with HA, and 1 was not multi-antibiotic resistant and PVL-positive, consistent with CA. Two isolates tested positive for PVL with one demonstrating both methicillin and fluoroquinolone (FQ) resistance. Of the 18 PVL-negative SA isolates, 15 (83%) were multi-antibiotic resistant (12 methicillin-resistant SA, 14 FQ resistant).

Conclusions: Our results reject the hypothesis that SA isolated from endophthalmitis is consistent with CA sources due to the lack of the PVL toxin and multiple resistant patterns of the SA. PVL does not appear to be a key virulence factor for the development of SA endophthalmitis.

FIG. 1.

Distribution of bacteria isolated from endophthalmitis (1993–2010) (n=518) provided by the Charles T. Campbell Ophthalmic Microbiology Laboratory, Pittsburgh, PA.