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Murali Sowmiya, Jambulingam Malathi, Hajib Naraharirao Madhavan; Screening of Ocular Enterobacteriaceae Isolates for Presence of Chromosomal blaNDM-1 and ESBL Genes: A 2-Year Study at a Tertiary Eye Care Center. Invest. Ophthalmol. Vis. Sci. 2012;53(9):5251-5257. doi: 10.1167/iovs.12-10467.
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Since, to our knowledge, there are no reports on the prevalence of the blaNDM-1 gene among ocular isolates of Enterobacteriaceae, and only limited information on the prevalence of extended spectrum beta-lactamases (ESBLs) among ocular bacterial isolates are available, our study was undertaken.
A prospective study was done on 74 Enterobacteriaceae isolates from patients presenting with clinical suspicion of bacterial ocular infections during a period from January 2010–December 2011. All isolates were subjected to detection of ESBLs by double disc synergy and screened for the presence of CTX-M –I, II, III, and IV groups, and OXA, TEM, SHV, blaNDM-1 genes by PCR.
Of 74 ocular Enterobacteriaceae isolates 57 (77%) were ESBL producers tested by the double disc diffusion test. PCR-based DNA sequencing of these 57 ocular isolates showed the presence of CTX-M-15 (14.0%), blaOXA-1 (5.2%), blaSHV-1 (8.7%), and blaTEM-1 (7.0%) types. The blaNDM-1 was absent among these ocular isolates. The most widely disseminated ESBL gene among ocular isolates was CTX-M-15. Phenotypic and genotypic results showed 100% correlation.
To our knowledge, this is the first extensive study performed to genotype ESBL-producing ocular Enterobacteriaceae isolates. The isolation of ESBL-producing Enterobacteriaceae organisms predominantly from conjunctival specimens indicates community-acquired infections/colonization by these bacteria in the conjunctiva of the patients, and cases are not related to hospital-acquired infections because of the short stay of ophthalmic patients in the hospitals. A shift in the resistance rates of ceftazidime from 37.5% to 79.7% over the years proves the increase in drug resistance among ocular clinical isolates.
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