Investigation of healthy horse eyes microbiota and evaluation of its antimicrobial susceptibility

Background: The conjunctiva of the eye is a mucosal surface that is colonised by various bacteria. Following surgery, trauma or other underlying conditions the normal flora may cause eye infection such as conjunctival and corneal infections, or endophthalmitis. Objectives: This study aimed to investigate the bacterial population and antibiotic resistance of the conjunctiva in healthy horses. Study designRandom sampling of ocular samples from 20 horses 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(degrees)C for 24-48 h. The isolated bacteria were characterised 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 the bacterial flora of the eyes to colistin, ceftiofur, florfenicol, amoxicillin and ampicillin between either different age groups or 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). A significant difference in sensitivity to trimethoprim-sulfamethoxazole between various sexes of horses was observed. Main limitations: The nonuniformity of the follow-up examination, reliance on owners or caregivers 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 individual bacteria comprising the bacterial flora in horses' eyes is influenced by housing and management conditions rather than age and sex.