Abstract
Background : The conjunctiva of the eye is a mucosal surface that is colonized by various bacteria. Following surgeries, trauma, or other underlying conditions the normal flora of these bacteria may cause some eye infections such as conjunctival, corneal infections, or endophthalmitis.
Objectives : This study aimed to investigate the bacterial population and antibiotic resistance of the conjunctiva in healthy horses.
Study design : Random sampling of ocular samples from 20 horse during the winter (2019).
Methods : Swab samples were collected from the eyes of 20 healthy horses of different breeds, ages, and sexes in Tehran province, Iran. The swabs were cultured on blood agar and MacConkey agar and incubated at 37°C for 24-48 hours. The isolated bacteria were characterized using cellular morphology, gram-staining, and biochemical tests. Sensitivity and resistance to 10 different antibiotics were measured using an antibiogram test.
Results : Results showed that the bacterial population consisted of various species, with Bacillus cereus being the most frequent. There were no significant differences in the frequency of isolated bacteria between sexes and age groups. There were no significant differences in the sensitivity of bacterial flora of the eyes to Colistin, ceftiofur, florfenicol, amoxicillin, and ampicillin between neither different age groups nor different sexes of the horses (P>0.05). However, sensitivity to enrofloxacin and ciprofloxacin was significantly correlated with the age groups of the horses (P>0.05). Significant difference in sensitivity to trimethoprim-sulfamethoxazole between various sexes of horses was observed.
Main limitations : The non-uniformity of the follow-up examination reliance owners or caregiver of the horse for follow-up information and Lack of adequate financial resources to study more horses.
Conclusions : The study suggests that the frequency of bacterial flora in horses’ eyes is influenced by housing and management conditions rather than age and sex.
Keywords: Microbial flora, Conjunctiva, Eyes, Horse, Mucosal surface.
Introduction
Eye surfaces are continually exposed to the environment, providing a habitat for different bacterial and fungal microorganisms. This microbiota contributes to the ocular defense mechanism by producing antibacterial substances that prevent colonization by pathogenic microorganisms (Chiang and Chern, 2022, LiYi and Wei, 2020). In physiological conditions, the surface of the eye is protected by several innate and adaptive immune systems, such as mucin and epithelium barrier functions, tear film that enables flushing of the ocular surface, antimicrobial tear components (lysozyme, beta-lysin, lactoferrin, blood cells, IgA), antigen-presenting cells and special antigen-recognition receptors called Toll-like receptors(Bolaños-Jiménez et al., 2015, Zak et al., 2018, SkopińskiKrawczyk and Ambroziak, 2013, Santibáñez et al., 2022). Eye infections are prevalent in horses, despite the protective mechanisms of the ocular surface. These infections are often caused by members of the conjunctival commensal microbiota that act as opportunistic pathogens after damage to the integrity of the ocular surface or surrounding areas(Santibáñez et al., 2022). The injured equine cornea may be more susceptible to infection due to the ubiquitous nature of bacteria and fungi in the outdoor or barn environment and the poor efficacy of host immune responses to prevent infection (Plummer, 2017). In horses, gram-positive bacteria are the predominant normal conjunctival flora, whereas gram-negative bacteria are isolated with greater frequency in eyes with extraocular disease(Zak et al., 2018). The most common gram-positive bacteria isolated from normal equine eyes are Staphylococcus, Streptococcus, Corynebacterium, and Bacillus spp. On the other hand, gram-negative bacteria such as Escherichia coli, Pseudomonas, Moraxella, Acinetobacter, and Neisseria spp are less frequently isolated from normal equine eyes. Fungal organisms such as Cladosporium, Alternaria, Fusarium, Aspergillus, and Penicillium spp have also been isolated from normal equine eyes (Hampson et al., 2019, Awosile et al., 2018). Several studies have shown the type of bacterial flora in the conjunctival sac may vary depending on the geographical location, the climate zone, age, and breed of the horses. Identifying the physiological commensal flora in the conjunctival sac is crucial for diagnosing inflammatory ocular disorders and selecting the most effective antibacterial treatment before obtaining antibiogram results(Johns et al., 2011). Risk factors for equine infectious keratitis include seasonal influences like weather, temperature, humidity as well as housing conditions, and use of topical corticosteroids and antimicrobials(MustikkaGrönthal and Pietilä, 2020, Tahoun et al., 2020). Bacterial resistance to certain antimicrobials was found to be higher in isolates obtained after antimicrobial treatment compared to those obtained before treatment(Hashemi et al., 2020, Hashemizadeh et al., 2022). This study aimed to investigate the population of bacterial flora in the eyes of healthy adult horses in Iran and to assess their antibiotic resistance to prevent the emergence of further antibiotic resistance in horses This study was also performed to identify any sex and age-related differences in bacterial populations and antibiotic resistance, which could be useful for developing targeted antibiotic therapies in the future.
Materials and methods