Ten-Year Trends and Clinical Relevance of the Antimicrobial Resistance Genotype in Respiratory Isolates of Streptococcus pneumoniae

Abstract

Background: Antimicrobial resistance of Streptococcus pneumoniae, especially against β-lactam antibiotics, is a global concern. We aimed to analyze a 10-year trend in the antimicrobial resistance genotype of respiratory isolates of S. pneumoniae and to clarify whether resistance genotypes were correlated with phenotypic drug susceptibility, pathogenicity, and host clinical background. Methods: Respiratory isolates of S. pneumoniae from 2003 to 2012 were analyzed with polymerase chain reaction for the presence of β-lactam resistance gene mutations on pbp1a, pbp2x, and pbp2b. Sixty-eight strains isolated from different patients in 2012 were particularly analyzed for the association between genotypes and clinical data. Results: The 10-year trend analysis showed a recent increase in gPRSP (genotypic penicillin-resistant S. pneumoniae) with all 3 β-lactam resistance genes (from 21.7 to 35.3% in 3 years) and a steady level of gPSSP (genotypic penicillin-susceptible S. pneumoniae) without any β-lactam resistance genes (13.2% in 2012). This resistance trend in genotypes was more prominent than resistance phenotypes determined with a drug susceptibility test. The probability of being a causative pathogen did not differ in gPSSP (55.6%), gPISP (genotypic penicillin-intermediate resistant S. pneumoniae; 54.3%), and gPRSP (54.2%). There was no significant difference in the ratio of patients who presented with respiratory failure in respiratory infection caused by gPSSP, gPISP, or gPRSP. Host clinical characteristics including age and gender were not different among resistance genotypes. Conclusions: There was no difference in pathogenicity or clinical background between gPSSP, gPISP, and gPRSP. Antimicrobial resistance in respiratory isolates of S. pneumoniae was more prevalent in genotypes than in phenotypes.