Prevalence of pilus genes in pneumococci isolated from healthy preschool children in Iceland: association with vaccine serotypes and antibiotic resistance.

Abstract

The objective of this study was to investigate the prevalence of pilus islets [pilus islet 1 (PI-1) and pilus islet 2 (PI-2)] in pneumococcal isolates from healthy Icelandic preschool children attending day care centres, prior to the introduction of conjugated pneumococcal vaccine, and the association of the pilus islets with vaccine serotypes and antibiotic resistance. Nasopharyngeal swabs were collected from 516 healthy children attending day care centres in Reykjavik in March and April 2009. Infant vaccination was started in 2011, thus the great majority of the children were unvaccinated. Pneumococci were cultured selectively, tested for antimicrobial susceptibility and serotyped. The presence of PI-1 and PI-2 was detected using PCR. A total of 398 viable isolates were obtained of which 134 (33.7%) showed the presence of PI-1. PI-1-positive isolates were most often seen in serotype 19F [30/31 (96.8%)] and were of clade I, and in 6B [48/58 (82.8%)] of clade II. PI-2-positive isolates were most common in serotype 19F [27/31 (87.1%)]; all of them were also PI-1 positive. Of the PI-1-positive and PI-2-positive isolates, 118 (88.1%) and 31 (81.6%), respectively, were of vaccine serotypes. Both PI-1 and PI-2 were more often present in penicillin-non-susceptible pneumococci (PNSP) than in penicillin-susceptible pneumococci [PI-1 in 41/58 (70.7%) and 93/340 (27.4%), respectively, and PI-2 in 28/58 (48.3%) and 10/340 (2.9%), respectively]. Genes for PI-1 and/or PI-2 in pneumococci isolated from healthy Icelandic children are mainly found in isolates of vaccine serotypes and in PNSP isolates belonging to multiresistant international clones that have been endemic in the country.