Pseudomonas Aeruginosa in Corneal Infections: Are They All the Same or Different?

Abstract

Purpose: : Multilocus sequence typing (MLST) is a bacterial typing system characterising isolates on the basis of the sequences of ~450 bp internal fragments of several housekeeping genes. We describe the use of MLST to study the population structure of Pseudomonas aeruginosa isolates to determine if strains from patients with microbial keratitis from the UK were genotypically different to those from China. We also wished to identify whether isolates from corneal infections represent a subgroup that differ from other clinical and environmental isolates.

Methods: : 117 P. aeruginosa isolates from keratitis and endophthalmitis infections were examined using the MLST scheme (79 from the UK and 38 from China). Seven housekeeping genes distributed around the P. aeruginosa genome were targets for PCR amplification. Nested primers amplified 366-495 bp fragments of each housekeeping gene. For each distinct allele within a locus an arbitrary number was assigned. Each isolate was therefore given seven numbers (allelic profile) that represented its sequence type (ST). Subsequence isolates with an identical allelic profile were assigned the same ST. Phylogenetic analyses of the strains were carried out using the START programme.

Results: : Based on BURST analysis, 98 STs were assigned to the 117 P. aeruginosa isolates. ST-235 was the most common ST (2 from China and 6 from around the UK). ST-244 was also found in China and the UK (3 isolates from China and 2 isolates from London). Another 2 Chinese isolates shared the same ST as a Manchester and a London isolate (ST-316). In the UK, 6 other pairs of isolates shared the same ST either from the same centre or from different centres. In China, 2 other pairs of isolates shared the same ST. The remaining isolates had a unique ST. Of all the P. aeruginosa eye infection isolates, 33 (28%) shared STs with previously identified STs from other clinical or environmental isolates already in the MLST online database and 84 (72%) had novel STs.

Keywords: microbial pathogenesis: experimental studies • pseudomonas • keratitis