Abstract
The purpose of this study was to compare bacterial isolation rate using a corneal impression membrane (CIM) and a sharp instrument for obtaining corneal samples from patients with suspected microbial keratitis (MK). Data was retrospectively collected for all patients that had corneal samples taken for presumed MK between May 2014 and May 2020. Prior to May 2017 samples were collected by scraping the edges of the ulcer with a blade. From May 2017, samples were collected by placing a CIM (Millicell cell culture insert) against the ulcer. All corneal samples were processed using the same conventional diagnostic culture method. A total of 3099 corneal samples were included, of which 1214 (39.2%) were corneal scrapes and 1885 (60.9%) CIMs. Microorganisms were isolated from 235 (19.4%) and 1229 (65.2%) cases using a corneal scrape and CIM, respectively (p < 0.001). Of routinely described pathogenic microorganisms, there were significant increases in the isolations of S. aureus (2.4% to 11.3%) and Serratia (0.5% to 1.7%) using the CIM and no significant changes in the isolations of S. pneumoniae and P. aeruginosa. No significant differences were seen between the isolation rates of fungi or Acanthamoeba species. There was a significant increase in the isolation rates of other Streptococcal species (0.7% to 6.9%) and CNS species, specifically, S. epidermidis (2.1% to 26.2%), S. capitis (0.4% to 2.6%) and S. warneri (0.3% to 1.6%) using the CIM. The simplified CIM sampling method is an effective method for collecting corneal samples from patients with presumed MK in clinical practice.
Highlights
Microbial keratitis (MK) is an ophthalmological emergency that can lead to sight threatening complications such as corneal scarring, perforation, endophthalmitis and blindness [1,2,3,4]
There was a significant increase in the number of corneal samples obtained in the 3-year period following the implementation of the corneal impression membrane (CIM) into clinical practice compared to the 3-year period prior to its implementation, despite numbers of ophthalmic emergency attendances remaining stable (Table 1)
We demonstrated that the introduction of a simplified CIM sampling method into clinical practice was associated with a significant increase in the number of corneal samples collected and in microorganism isolation rates
Summary
Microbial keratitis (MK) is an ophthalmological emergency that can lead to sight threatening complications such as corneal scarring, perforation, endophthalmitis and blindness [1,2,3,4]. The need to detect bacteria, fungi, yeasts and protozoa together with the fact that there may be relatively few microorganisms in a corneal ulcer, means that an adequate sample must be obtained and cultured on a variety of different media [5] This has led to the traditional practice of taking multiple samples by scraping the edges of the ulcer with a blade, needle or spatula and directly plating the material onto several culture media. This, in addition to good activity of fourth generation fluoroquinolones, may explain the reluctance of some ophthalmologists to perform a corneal scrape to reach a microbiological diagnosis [7,8] It lection of samples and the detection and diagnosis of microorganisms in suspecte In 2015, we developed a minimally invasive sampling method using an im membrane made from polytetrafluroethylene (PTFE) [9].
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