Abstract
Purpose :
To assess the in-vitro drug susceptibility of the Pythium sp. and its correlation with the clinical outcomes.
Methods :
This study reviewed clinical outcome of patients with culture proven Pythium keratitis seen from January 2016 to July 2020. Zoospores derived from culture isolates were used for antibiotic susceptibility testing using disc diffusion method. The results were expressed in zone of inhibition (ZOI in mm). Clinical outcomes were divided into two groups: patients with clinical resolution on medical therapy (combination of topical linezolid 0.2% and azithromycin 1%) and patients who needed therapeutic penetrating keratoplasty (TPK). Based on ZOI for linezolid and azithromycin, the patients were divided into 4 groups i.e. <30 mm (group1), 31-35 mm (group2),36-39 mm (group 3), and >40 mm (group 4). Proportion of clinical resolution and need for TPK in each group were compared.
Results :
There were total 129 culture proven cases (M: F ratio was 50:79) of Pythium keratitis. Average age of the patients was 42.6 ±15 years. Median size of the infiltrate (vertical x horizontal) was 5.8(4-7.5) x5.6(4.3-7.5) mm. Out of 129 patients, 60(46.5%) got resolved on medical treatment, while 62(48.1%) needed TPK and 7 patients were lost to follow-up. Clinical and demographical profile of cases with resolved and worsened infection were comparable. There were N=14,65,38 and 12 patients in zone 1,2,3,4 respectively. Number of TPK were more(65.2%) in group 1 as compared to group 4(8.3%), p=0.032. There were 31(47.7%) and 21(55%) patients who underwent TPK from group 3 and 4 respectively. No clinical correlation could be found with the susceptibility of Pythium with azithromycin.
Conclusions :
In absence of CLSI guidelines for interpretation of ZOI for Pythium isolates, based on clinical response, this study recommends the consideration of a ZOI less than 30 mm as resistant to linezolid while ZOI greater than 40 mm can be considered susceptible and ZOI between 31-39 may be considered as intermediate susceptibility.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.