Methicillin-resistant Staphylococcus aureus ulcerative keratitis in a Thoroughbred racehorse

Bacterial and fungal isolates from 107 cases of ulcerative keratitis in Japanese Thoroughbred racehorses (2017-2021)

Infectious ulcerative keratitis is a common disease in racehorses. To improve treatment outcomes, this study aimed to assess the antimicrobial susceptibilities of bacterial and fungal isolates obtained from the cornea of Japanese Thoroughbred racehorses with equine infectious ulcerative keratitis. Bacterial and fungal cultures were performed for 166 corneal swabs from 107 cases. A disc diffusion test and minimum inhibitory concentration test were also performed to assess antimicrobial susceptibility of the bacterial and fungal isolates, respectively. Bacterial and/or fungal isolates were obtained from 85.0% (91/107) of the cases. Staphylococcus was primarily isolated from bacterial isolates, including methicillin-resistant Staphylococcus aureus (MRSA), Aerococcus, Streptococcus, Acinetobacter, and Pseudomonas. Aspergillus was primarily isolated from filamentous fungi, and Debaryomyces species was primarily identified in yeast-like fungi. Ofloxacin resistance was observed in 100% (12/12), 15.9% (7/44), and 25.0% (3/12) of MRSA, Staphylococcus, and Streptococcus isolates, respectively. The prevalence of quinolone-resistant Staphylococci and Streptococci has increased in the past two decades. All Aspergillus isolates were susceptible to voriconazole, whereas other filamentous fungi, including Fusarium, were less susceptible to voriconazole. Further studies are required to determine effective treatments for antimicrobial-resistant isolates.

The Prevalence and Molecular Biology of Staphylococcus aureus Isolated from Healthy and Diseased Equine Eyes in Egypt

This work aimed to characterize S. aureus isolates from the eyes of healthy and clinically affected equines in the Kafrelsheikh Governorate, Egypt. A total of 110 animals were examined for the presence of S. aureus, which was isolated from 33 animals with ophthalmic lesions and 77 healthy animals. We also investigated the antimicrobial resistance profile, oxacillin resistance mechanism, and the major virulence factors implicated in many studies of the ocular pathology of pathogenic S. aureus. The association between S. aureus eye infections and potential risk factors was also investigated. The frequency of S. aureus isolates from clinically affected equine eyes was significantly higher than in clinically healthy equids. A significant association was found between the frequency of S. aureus isolation from clinically affected equine eyes and risk factors including age and season but not with sex or breed factors. Antimicrobial resistance to common antibiotics used to treat equine eyes was also tested. Overall, the isolates showed the highest sensitivity to sulfamethoxazole (100%) and the highest resistance to cephalosporin (90.67%) and oxacillin (90.48%). PCR was used to demonstrate that mecA was present in 100% of oxacillin- and β-lactam-resistant S. aureus strains. The virulence factor genes Spa (x region), nuc, and hlg were identified in 62.5%, 100%, and 56%, of isolates, respectively, from clinically affected equines eyes. The severity of the eye lesions increased in the presence of γ-toxin-positive S. aureus. The phylogenetic tree of the Spa (x region) gene indicated a relationship with human reference strains isolated from Egypt as well as isolates from equines in Iran and Japan. This study provides insight into the prevalence, potential risk factors, clinical pictures, zoonotic potential, antimicrobial resistance, and β-lactam resistance mechanism of S. aureus strains that cause eye infection in equines from Egypt.

Conjunctival aerobic bacterial flora in healthy Silesian foals and adult horses in Poland

Background

Commensal bacterial and fungal flora of the conjunctival sac has been described in horses and other animals. The identification of commensal flora of the conjunctival sac may aid in the diagnosis of ocular inflammatory diseases, such as conjunctivitis or more severe ulcerative keratitis, common in horses. Moreover, damage of ocular protective barriers may lead to an opportunistic infection. The study was carried out in Silesian horses kept at a single breeding center in South-western Poland, in order to limit any breed-dependant and climate-dependant variables affecting the results. Following an ophthalmic examination that revealed no abnormalities, sterile swabs were collected from conjunctival sac in 26 adult horses and 11 foals. The obtained swabs were subjected to bacterial culture testing. In case of Staphylococcus spp. isolation, susceptibility to methicillin was evaluated.

Results

Forty- three bacterial isolates, representing eleven genera of bacteria were cultured from 30 (81%) horses. Gram-positive bacteria were the dominant isolates (72%) (p < 0.001). The most commonly isolated Gram-positive bacteria were Staphylococcus spp., while Moraxella spp. were the most frequently isolated Gram-negative bacteria. There was no significant influence of sex and age on the frequency and type of microbial isolates.

Conclusions

Commensal flora is present in the conjunctival sac of healthy horses in Poland. Age does not affect the abundance and type of microbial isolates.

Identification and antimicrobial susceptibility of microorganisms isolated from severe corneal ulcers of dogs in Thailand

This study aims to determine the microbiological profile and risk factors associated with antimicrobial-resistant bacteria in canine severe corneal ulcers. Thirty-two corneal and conjunctival swabs were collected from dogs with diagnosed severe corneal ulcers that presented to Prasu-Arthorn veterinary teaching hospital in Nakhon Pathom, Thailand from June 2015 to June 2016. Microorganisms were identified by means of genotypic and phenotypic approaches. Of 32 ulcers sampled, 26 (81.3%) yielded culturable microorganisms with 24 bacterial isolates and 7 fungal isolates. The most commonly isolated bacteria were Staphylococcus spp. (45.8%, 11/24) and Pseudomonas aeruginosa (20.8%, 5/24). Out of 11 staphylococcal isolates identified, 10 carried the mecA gene providing methicillin resistance. The extended-spectrum β-lactamase (ESBL) encoding genes blaCTX-M and blaVEB-1 were found in an Acinetobacter lwoffii isolate, and blaSHV was found in a P. aeruginosa isolate. Based on the Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoint criteria, minimum inhibitory concentrations values showed that all bacteria, except for staphylococci, were susceptible to current ophthalmic antibiotics. More than 50% of staphylococci were resistant to all generations of fluoroquinolones and fusidic acid. Chloramphenicol was highly active against staphylococci (81.3% susceptible). The width (P=0.02) and the depth (P=0.04) of ulcers predicted greater risk of yielding resistant bacteria. The identification of antimicrobial-resistant bacteria prompts practitioners to be prudent when choosing ophthalmic antibiotics for severe corneal ulcers.

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.

Altering equine corneal fibroblast differentiation through Smad gene transfer

OBJECTIVE

To explore the impact of equine corneal fibroblast (ECF) to myofibroblast (ECM) differentiation by altering the expression of the Smad genes either individually or in combination. Specifically, we sought to examine the ECF differentiation after (a) silencing of Smad2, 3, and 4 profibrotic genes individually and (b) overexpression of antifibrotic Smad7 gene and in a combination with pro- and antifibrotic Smad genes.

METHODS

Equine corneal fibroblast primary cultures were generated as previously described. ECFs were transfected with individual plasmids which silenced gene expression of either Smad2, 3, or 4 or in combination with a plasmid overexpressing Smad7 using Lipofectamine 2000™ or Lipofectamine BLOCK-iT™. Smad-transfected clones were then exposed to TGF-β1 to induce differentiation to myofibroblasts. Immunofluorescence and qRT-PCR techniques quantified levels of ECF differentiation to ECM by measuring alpha smooth muscle actin, a known marker of ECM transdifferentiation.

RESULTS

Silencing of individual Smad2, 3, or 4 genes or overexpression of Smad7 showed significant inhibition of ECF transdifferentiation (73-83% reduction). Silencing of Smad2 showed the greatest inhibition of ECF transdifferentiation in (a) and was therefore utilized for the combination gene transfer testing. The combination gene transfer consisting of Smad7 overexpression and Smad2 silencing attenuated ECF differentiation significantly; however, the level was not significant compared to the overexpression of Smad7 individually.

CONCLUSIONS

Using gene transfer technology involving profibrotic Smad silencing, antifibrotic Smad overexpression or its combination is a novel strategy to control TGF-β1-mediated fibrosis in equine fibroblasts. Combination gene therapy was not better than single gene therapy in this study.

Meticillin-resistant Staphylococcus aureus colonisation and infection in Thoroughbred racehorses and veterinarians in Japan

Meticillin-resistant Staphylococcus aureus (MRSA) infections have been confirmed in hospitalised Thoroughbred racehorses at the hospitals of two training centres in Japan since 2009. To investigate the source of infection, the authors examined the rate of nasal MRSA colonisation in 600 healthy Thoroughbred racehorses, 53 veterinarians and 16 office staff at the racehorse hospitals of the two training centres. MRSA was not isolated from healthy Thoroughbred racehorses or hospital office staff. However, MRSA was isolated from 16 veterinarians (30.1 per cent), and the colonisation rate was significantly higher in veterinarians than in the office staff of the same hospitals. Also, 10 of the 16 MRSA strains (62.5 per cent) isolated from veterinarians were classified as type II by staphylococcal cassette chromosome mec (SCCmec) typing and ST5 by multilocus sequence typing. Pulsed-field gel electrophoresis analysis demonstrated that these 10 MRSA strains of SCCmec type II and ST5 were genetically identical or very similar to 9 MRSA strains isolated from infected horses hospitalised at these hospitals between 2009 and 2013. These results indicate that SCCmec type II and ST5 MRSA strains were probably transmitted between veterinarians and infected horses.