Abstract
Transmission of antibiotic resistance genes among Streptococcus pneumoniae and beta-hemolytic streptococcus (BHS) was generally associated with transmissible genetic elements. The objectives of this study were to investigate carriage rate, antibiotic resistance and related mobile genetic elements of pneumococci and BHS from school-children. The pneumococci and BHS were recovered from 220 Thai school-children, and then tested for antibiotic susceptibility pattern by disc diffusion. Antibiotic resistance genes and related genetic elements were detected by PCR with specific primers. A total of 77 pneumococcal isolates were resistant to erythromycin (42 %), tetracycline (44 %), clindamycin (8 %), or penicillin (3 %). Fifty-four BHS isolates were resistant to erythromycin (28 %), tetracycline (52 %), or clindamycin (13 %). All isolates tested were 100 % sensitive to penicillin and levofloxacin. Among erythromycin-resistant streptococcal isolates showed different phenotypes of clindamycin resistance. It was found that isolated pneumococci showed constitutive clindamycin resistance (19 %), and inducible clindamycin resistance (12 %). The BHS isolates exhibited constitutive clindamycin resistance (40 %), and inducible resistance (20 %) phenotypes. The predominant erythromycin resistance genes in pneumococci and BHS were mefE and ermB, while the most common tetracycline resistance gene in this population was tetM. Furthermore, almost all erythromycin- and tetracycline-resistant streptococci (97 %) mainly contained various genetic elements, including mega elements and six different transposon types (Tn2009, Tn2017, Tn917, Tn3872, Tn6002 and Tn916). Therefore, carriages of pneumococci and BHS with multidrug resistance in children might be important reservoirs of antibiotic-resistance genes carried by transposons. Tn916-like elements could lead to dissemination of the antibiotic resistance genes among genus streptococcus in human oral cavity and nasopharynx.