Changes in antimicrobial resistance patterns of ocular surface bacteria isolated from horses in the UK: An eight‐year surveillance study (2012‐2019)

Abstract

Purpose To identify temporal changes in antimicrobial resistance of ocular surface bacteria isolated from clinically symptomatic equine eyes in the South West of the UK. Study design Retrospective. Methods Clinical and laboratory records of horses treated for suspected bacterial ocular surface disease (ulcerative and non‐ulcerative) at a single facility between January 2011 and December 2019 were reviewed. Cases were included if they underwent ocular surface sampling, aerobic bacterial culture, and antimicrobial susceptibility testing. Cases were split into two time periods based on when sampling occurred: “early” (2012‐2015) and “late” (2016‐2019) to enable identification of temporal trends in resistance to chloramphenicol, gentamicin, fusidic acid, neomycin, cloxacillin, ofloxacin, and polymyxin B. Results A total of 125 samples from 110 horses were included in analyses. Culture‐positive isolates were identified in 76/110 (60.8%) samples. Principal isolates included Staphylococci spp. (n = 45; 64.3%), Streptococci spp. (n = 14; 20%), and Enterobacter spp. (n = 11; 15.7%). There was a significant increase in resistance to chloramphenicol over time (P = .007) and a decrease in resistance to ofloxacin that approached significance (P = .059). Chloramphenicol (100%) and gentamicin (85.7%) had the highest overall in‐vitro efficacy during the early and late periods, respectively. There was no significant difference in the type of bacteria isolated across the two time periods. Conclusions These results suggest a potential increase in resistance to chloramphenicol among bacteria isolated from the ocular surface of horses in the South West UK, reinforcing the value of surveillance to guide the empirical use of antimicrobials.

Equine ulcerative keratitis in Belgium: Associated bacterial isolates and in vitro antimicrobial resistance in 200 eyes

“…Aminoglycosides used to be advocated as effective therapy for infectious keratitis 5 . In contrast to earlier studies 7,14 but in accordance with Sauer et al, 9 our study demonstrated lower susceptibility profiles among ocular isolates to gentamicin and tobramycin. Although they both showed to be effective against the majority of Staphylococcus spp.…”

“…However, these results are in line with those of Switzerland 13 and Finland 11 when chloramphenicol is tested against staphylococci and streptococci separately. In a study from Chalder et al, 7 an increase in resistance was noted from 0% to 30% of ocular surface bacteria to chloramphenicol, isolated from diseased equine eyes in the UK. This could be a result of its empirical topical use in bacterial keratitis in the UK, which is not the case in Belgium yet.…”

“…However, in our study, gram‐negative bacteria together with MRS were generally more resistant to fluoroquinolones compared with gram‐positive bacteria. The concern over the emerging resistance among ocular pathogens of fluoroquinolones 6 could not be proven in the UK 7 but a potentially high degree of variability among isolates in different geographic regions must be kept in mind. According to Belgium's guidelines for the responsible use of antibiotics, 28 fluoroquinolones should not be used for routine topical prophylaxis and be limited to cases of infectious keratitis confirmed by microbial isolation and based on antimicrobial susceptibility results.…”

“…The main objective of an antimicrobial treatment is a rapid elimination of the pathogen, preventing the release of proteases and toxins, and obtaining control of the innate PMN driven inflammation responsible for the progressive destructive process of the cornea 6 . Increasing antimicrobial resistance has been reported in several common bacterial pathogens 4,7–9 . In addition, overuse or inappropriate use of topical antimicrobial drugs is shown to alter the ocular surface microflora and may be responsible for the development of antimicrobial resistance 10…”

“…6 Increasing antimicrobial resistance has been reported in several common bacterial pathogens. 4,[7][8][9] In addition, overuse or inappropriate use of topical antimicrobial drugs is shown to alter the ocular surface microflora and may be responsible for the development of antimicrobial resistance. 10 A variation in bacterial isolate and antimicrobial susceptibility has been demonstrated to depend on geographical location, season, and previous antimicrobial therapy.…”