Abstract
BackgroundStreptococcus pneumoniae is the main pathogen that causes respiratory infections in children younger than five years. The increasing incidence of macrolide- and tetracycline-resistant pneumococci among children has been a serious problem in China for many years. The molecular characteristics of erythromycin-resistant pneumococcal isolates that were collected from pediatric patients younger than five years in Beijing in 2010 were analyzed in this study.ResultsA total of 140 pneumococcal isolates were collected. The resistance rates of all isolates to erythromycin and tetracycline were 96.4% and 79.3%, respectively. Of the 135 erythromycin-resistant pneumococci, 91.1% were non-susceptible to tetracycline. In addition, 30.4% of the erythromycin-resistant isolates expressed both the ermB and mef genes, whereas 69.6% expressed the ermB gene but not the mef gene. Up to 98.5% of the resistant isolates exhibited the cMLSB phenotype, and Tn6002 was the most common transposon present in approximately 56.3% of the resistant isolates, followed by Tn2010, with a proportion of 28.9%. The dominant sequence types (STs) in all erythromycin-resistant S. pneumoniae were ST271 (11.9%), ST81 (8.9%), ST876 (8.9%), and ST320 (6.7%), whereas the prevailing serotypes were 19F (19.3%), 23F (9.6%), 14 (9.6%), 15 (8.9%), and 6A (7.4%). The 7-valent pneumococcal conjugate vaccine (PCV7) and 13-valent pneumococcal conjugate vaccine (PCV13) coverage of the erythromycin-resistant pneumococci among the children younger than five years were 45.2% and 62.2%, respectively. ST320 and serotype 19A pneumococci were common in children aged 0 to 2 years. CC271 was the most frequent clonal complex (CC), which accounts for 24.4% of all erythromycin-resistant isolates.ConclusionsThe non-invasive S. pneumoniae in children younger than five years in Beijing presented high and significant resistance rates to erythromycin and tetracycline. The expressions of ermB and tetM genes were the main factors that influence pneumococcal resistance to erythromycin and tetracycline, respectively. Majority of the erythromycin-resistant non-invasive isolates exhibited the cMLSB phenotype and carried the ermB, tetM, xis, and int genes, suggesting the spread of the transposons of the Tn916 family. PCV13 provided higher serotype coverage in the childhood pneumococcal diseases caused by the erythromycin-resistant isolates better than PCV7. Further long-term surveys are required to monitor the molecular characteristics of the erythromycin-resistant S. pneumoniae in children.
Highlights
Streptococcus pneumoniae is the main pathogen that causes respiratory infections in children younger than five years
Pneumococcal macrolide resistance is mediated by two major mechanisms, namely, target modification by a ribosomal methylase encoded by the ermB gene and drug efflux encoded by the mef gene
Up to 98.5% (133/135) of the erythromycin-resistant pneumococcal isolates exhibited high minimum inhibitory concentrations (MICs) (>256 μg/mL)
Summary
Streptococcus pneumoniae is the main pathogen that causes respiratory infections in children younger than five years. Streptococcus pneumoniae, the main pathogen that causes respiratory infections in children younger than five years, can cause various pneumococcal diseases, such as otitis media, sinusitis, pneumonia, meningitis, pleurisy, and bacteremia. The increasing resistance of S. pneumoniae to various antibiotics, including macrolides and tetracyclines, makes pneumococcal infections difficult to treat especially in children and in regions like China. Pneumococcal macrolide resistance is mediated by two major mechanisms, namely, target modification by a ribosomal methylase encoded by the ermB gene and drug efflux encoded by the mef gene. Pneumococcal resistance to erythromycin and tetracycline is frequently associated with the insertion of the ermB gene into the transposons of the Tn916 or Tn917 family (Tn6002, Tn2010, Tn3872, Tn1545, and Tn6003) that contains the tetM gene
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