Occurrence and molecular composition of methicillin-resistant Staphylococcus aureus isolated from ocular surfaces of horses presented with ophthalmologic disease.

Severe infections due to methicillin-resistant Staphylococcus aureus (MRSA) have been increasingly recognized in virtually all fields of veterinary medicine. Our objective was to study the occurrence, phylogenetic relationships and antimicrobial resistance properties of MRSA isolated from ocular surfaces of horses prior to invasive procedures. Within a 49-week sampling period, ocular swabs obtained from 46 eyes of 44 horses, including eyes with clinical signs of conjunctivitis/blepharitis, keratitis or uveitis were screened for the presence of S. aureus. As a result, seven samples were positive for S. aureus (15.2%), with six of them being classified as MRSA (13%). In addition, all isolates were resistant or showed reduced susceptibility to tetracyclines, the aminoglycosides gentamicin and kanamycin, fluoroquinolones, and the combination sulfamethoxazole/trimethoprim. Since a very close relationship between the MRSA isolates was assumed after pulsed-field gel electrophoresis employing the restriction endonuclease ApaI, whole genome sequencing (WGS) was used to shed more light on the phylogenetic relationships and the molecular composition of all MRSA isolates. Analysis of WGS data revealed closely related MRSA belonging to sequence type 398, spa type t011 and dru type dt10q, harboring an SCCmec IV element and the Staphylococcus aureus pathogenicity island SaPIbov5. Moreover, all MRSA were positive for a beta-hemolysin converting phage carrying genes of the immune evasion cluster (IEC). Since cases of eye infections due to MRSA were often associated with fatal outcomes, more research is needed with respect to the origin of MRSA isolated from ocular surfaces to implement sufficient barrier and infection control measures.

Diabetes mellitus leads to accumulation of dendritic cells and nerve fiber damage of the subbasal nerve plexus in the cornea.

PURPOSE: To evaluate whether nerve fibers of the subbasal nerve plexus (SNP) and dendritic cells (DCs) are in association with each other leading to neuropathy in the diabetic cornea. METHODS: BALB/c mice were injected with streptozotocin (STZ) for 5 days for induction of diabetes mellitus (DM) or with vehicle solution (control). B6.VLep(ob/ob) (ob/ob) mice served as an obese and glucose-intolerant DM type 2 (DM II) model and lean B6.VLep(ob/+) (ob/+) mice as respective controls. Using in vivo corneal confocal microscopy (CCM), nerve fibers and DCs were quantified over a period of 9 weeks and additionally analyzed by in vitro immunofluorescence whole-mount staining. RESULTS: In STZ-diabetic mice, CCM revealed an increase of DC density (DCD) in contrast to controls, whereas nerve fiber density (NFD) was decreased with duration of DM. In ob/ob mice, DCD was 3-fold higher than in both ob/+ mice and STZ-diabetic mice. Whole-mount staining displayed CD11c(+) and major histocompatibility complex (MHC) class II(+) mature DCs in colocalization with class III ß-tubulin(+) nerve fibers in the cornea. CONCLUSIONS: Hyperglycemia leads to corneal DC infiltration, and obesity aggravates this immune response. The direct contact between DCs and the SNP can be assumed to be a trigger of nerve fiber damage and thus a contributing factor to polyneuropathy in diabetic corneas.