Abstract
Purpose :
Colistin is considered the last line of defence against multi-drug resistant gram negative bacterial (GNB) infections. The purpose of this study was to determine prevalence, clinical outcome and susceptibility patterns to non-colistin antibiotics.
Methods :
Clinical and microbiological data were collected from consecutive cases of GNB microbial keratitis, infectious endophthalmitis and orbital infections over 1 year. Isolates were identified by standard microbiological procedures, confirmed by Vitek 2 compact system and screened for colistin resistance by Broth Microdilution method. Other GNB panel antibiotics were tested by Kirby-Bauer disc diffusion method. Clinical outcome criteria are given in Table 1. Screening for plasmid mediated CLR was done by plasmid DNA extraction and PCR with mcr-1and mcr-2 probes. The primary aim was to determine prevalence of CLR in ocular GNB isolates in different ocular infections. Secondary aim was to correlate colistin resistance with clinical outcomes and to determine susceptibility of CLR isolates to non-colistin antibiotics.
Results :
Of the 60 GNB isolates, 40% (n=24) were colistin resistant (~45% in keratitis and endophthalmitis, and 28% in others; Table 2). Poorer clinical outcome in the CLR group, was noted only in orbital infections (95% CI= 1.3- 20, RR=5.2, P=0.02), while in microbial keratitis and endophthalmitis groups, clinical outcomes were comparable between CLR and colistin sensitive (CLS) groups. Significantly higher resistance to amikacin, gentamycin and ceftazidime was seen in CLR isolates. No difference with CLS group was noted for other GNB panel antibiotics including quinolones and imipenem. Of the 16 isolates tested, plasmid mcr-1 mediated colistin resistance was seen in 1 isolate of Enterobacter cloacae while mcr-2 mediated resistance was seen in 3 isolates of Burkholderia cepacia and 1 isolate of Pseudomonas aeruginosa.
Conclusions :
CLR, though widely prevalent in ophthalmic infections, probably has limited impact on clinical outcomes of these infections. Routine GNB antibiotics may not be effective in CLR infections. Finally, plasmid-mediated transfer may account for transmission of CLR in ocular infections.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.