Susceptibility of Ocular Staphylococcus aureus to Antibiotics and Multipurpose Disinfecting Solutions

Abstract

Staphylococcus aureus is a frequent cause of ocular surface infections worldwide. Of these surface infections, those involving the cornea (microbial keratitis) are most sight-threatening. S. aureus can also cause conjunctivitis and contact lens-related non-infectious corneal infiltrative events (niCIE). The aim of this study was to determine the rates of resistance of S. aureus isolates to antibiotics and disinfecting solutions from these different ocular surface conditions. In total, 63 S. aureus strains from the USA and Australia were evaluated; 14 were from niCIE, 26 from conjunctivitis, and 23 from microbial keratitis (MK). The minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) of all the strains to ciprofloxacin, ceftazidime, oxacillin, gentamicin, vancomycin, chloramphenicol, azithromycin, and polymyxin B were determined. The MIC and MBC of the niCIE strains to contact lens multipurpose disinfectant solutions (MPDSs) was determined. All isolates were susceptible to vancomycin (100%). The susceptibility to other antibiotics decreased in the following order: gentamicin (98%), chloramphenicol (76%), oxacillin (74%), ciprofloxacin (46%), ceftazidime (11%), azithromycin (8%), and polymyxin B (8%). In total, 87% of all the isolates were multidrug resistant and 17% of the isolates from microbial keratitis were extensively drug resistant. The microbial keratitis strains from Australia were usually susceptible to ciprofloxacin (57% vs. 11%; p = 0.04) and oxacillin (93% vs. 11%; p = 0.02) compared to microbial keratitis isolates from the USA. Microbial keratitis isolates from the USA were less susceptible (55%) to chloramphenicol compared to conjunctivitis strains (95%; p = 0.01). Similarly, 75% of conjunctivitis strains from Australia were susceptible to chloramphenicol compared to 14% of microbial keratitis strains (p = 0.04). Most (93%) strains isolated from contact lens wearers were killed in 100% MPDS, except S. aureus 27. OPTI-FREE PureMoist was the most active MPDS against all strains with 35% of strains having an MIC ≤ 11.36%. There was a significant difference in susceptibility between OPTI-FREE PureMoist and Biotrue (p = 0.02). S. aureus non-infectious CIE strains were more susceptible to antibiotics than conjunctivitis strains and conjunctivitis strains were more susceptible than microbial keratitis strains. Microbial keratitis strains from Australia (isolated between 2006 and 2018) were more susceptible to antibiotics in comparison with microbial keratitis strains from the USA (isolated in 2004). Most of the strains were multidrug-resistant. There was variability in the susceptibility of contact lens isolates to MPDSs with one S. aureus strain, S. aureus 27, isolated from niCIE, in Australia in 1997 being highly resistant to all four MPDSs and three different types of antibiotics. Knowledge of the rates of resistance to antibiotics in different conditions and regions could help guide treatment of these diseases.

Virulence Genes of Staphylococcus aureus Associated With Keratitis, Conjunctivitis, and Contact Lens–Associated Inflammation

“…However, mecA was not seen in any infection strains from Australia (0%) vs infection strains from the United States (35%; P = 0.0001) ( Supplementary Table S3 ). Oxacillin susceptibility of these strains have been previously published, 33 and there was a significant correlation between possession of mecA and oxacillin resistance (correlation coefficient, rs = 0.48, P = 0.005). The only other correlation was a negative association between possession of mecA and scpA (rs = −0.40, P = 0.001).…”

“…Previously reported antibiotic susceptibility data of these isolates 33 demonstrated that although most of the strains were MDR, noninfectious (niCIE) strains were more susceptible to antibiotics than conjunctivitis strains, and conjunctivitis strains were more susceptible than MK strains. MK strains from Australia were more susceptible compared with MK strains from the United States.…”

“…One MDR strain from niCIE group ( S. aureus , 27) had a higher minimum inhibitory concentration to all tested multipurpose disinfectant solutions. 33 The correlation between possession of mecA and oxacillin resistance was expected. The negative association between the possession of mecA and scpA might suggest some incompatibility between the possession of these genes or their associated mobile genetic elements, and this finding should be examined in future studies.…”

Genomics of Staphylococcus aureus Strains Isolated from Infectious and Non-Infectious Ocular Conditions

“…The genomic make-up of S. aureus influences the virulence of its strains and pathogenicity associated with its disease [ 11 ]. The antibiotic susceptibility data of the isolates previously reported [ 12 ] and used in this study demonstrated that although most of the strains were multi-drug resistant (MDR), the non-infectious (niCIE) strains were more susceptible to antibiotics (ciprofloxacin, ceftazidime, oxacillin) than were the conjunctivitis strains, and the conjunctivitis strains were more susceptible to antibiotics (chloramphenicol, azithromycin) than were the MK strains [ 12 ]. MK strains from Australia were more susceptible to antibiotics (ciprofloxacin, oxacillin) compared to MK strains from USA [ 12 ].…”

“…The antibiotic susceptibility data of the isolates previously reported [ 12 ] and used in this study demonstrated that although most of the strains were multi-drug resistant (MDR), the non-infectious (niCIE) strains were more susceptible to antibiotics (ciprofloxacin, ceftazidime, oxacillin) than were the conjunctivitis strains, and the conjunctivitis strains were more susceptible to antibiotics (chloramphenicol, azithromycin) than were the MK strains [ 12 ]. MK strains from Australia were more susceptible to antibiotics (ciprofloxacin, oxacillin) compared to MK strains from USA [ 12 ]. Whilst several studies have examined which virulence factors might be involved in the development of keratitis by S. aureus , there is much less information on the association of virulence factors with conjunctivitis or niCIE [ 13 ].…”