7% erythromycin

resistance in Shanghai [20] and Stem Cell Compound Library clinical trial 92.1% in Chongqing [21]. In the present study, the erythromycin resistance rate of S. pneumoniae was higher at 96.4%, and most of the isolates had high MICs (>256 μg/mL), which indicated an increasing trend of pneumococcal erythromycin resistance in the hinterlands of China. Geographical variations were observed in the phenotypic and genotypic characteristics of erythromycin-resistant S. pneumoniae. The ermB gene was the most common mechanism for erythromycin resistance in the hinterlands of China, Taiwan, Sri Lanka, and Korea, similar to the results of this study for the children in Beijing. However, the mef gene was more common in Hong Kong, Singapore, Thailand, and Malaysia [18]. In Europe, the ermB gene was the dominant macrolide-resistance gene, especially in France, Spain, Switzerland, and Poland. On the other hand, the mef gene was common in Greece and Germany [22]. In the present

study, the MLSB phenotype was the predominant phenotype among the erythromycin-resistant pneumococcal isolates, which was in accordance with previous studies in China [23, 24]. However, the M phenotype was more prevalent than the MLSB phenotype in other countries, such as in Canada PLX4032 and in the United Kingdom [9, 25]. The resistance of S. pneumoniae to tetracycline was also significantly high in China, which was similar to that of erythromycin. This result may be related to the abuse of tetracycline in agriculture and edible animals. A multi-center research on the antibiotic resistance of S. pneumoniae involving four cities in China revealed that 82.1% of pneumococcal isolates were tetracycline-resistant among 1-month-old to 5-year-old children with acute upper respiratory infections [23]. The tetracycline non-susceptible rate among the invasive erythromycin-resistant pneumococcal isolates collected in Australia was 75.5% [26]. This value

was lower than the non-invasive erythromycin-resistant isolates in the current study. The present study, in addition to previous ones [10, 11, 27], proved that the tetM gene was responsible Baf-A1 cell line for tetracycline resistance in S. pneumoniae. In the present study, we found that the eight pneumococcal isolates with the tetM gene were susceptible to tetracycline. Amezaga et al. [9] identified a 10 bp deletion in the sequence of the tetM gene of one tetracycline-susceptible isolate. This result was relative to the tetM sequence in tetracycline-resistant isolates. Thus, further studies are necessary. Tetracycline resistance is associated with erythromycin resistance in pneumococcal isolates, which are transmitted by the transposons of the Tn916 or Tn917 family including Tn6002, Tn2010, Tn3872, Tn1545, and Tn6003. Tn6002, which was first detected in Streptococcus cristatus, originated from the insertion of an ermB-containing DNA fragment into Tn916, which carries the tetM gene [28, 29].