Genetic Determinants of Tetracycline Resistance in Clinical Streptococcus pneumoniae Serotype 1 Isolates from Niger

Streptococcus pneumoniae serotype 1 is the first cause of pneumococcal meningitis Niger. To determine the underlying mechanism of resistance to tetracycline in serotype 1 Streptococcus pneumoniae, a collection of 37 isolates recovered from meningitis patients over the period of 2002 to 2009 in Niger were analyzed for drug susceptibility, and whole genome sequencing (WGS) was performed for molecular analyses. MIC level was determined for 31/37 (83.8%) isolates and allowed detection of full resistance (MIC = 8 µg) in 24/31 (77.4%) isolates. No resistance was found to macrolides and quinolones. Sequence-types deduced from WGS were ST217 (54.1%), ST303 (35.1%), ST2206 (5.4%), ST2839 (2.7%) and one undetermined ST (2.7%). All tetracycline resistant isolates carried a Tn5253 like element, which was found to be an association of two smaller transposons of Tn916 and Tn5252 families. No tet(O) and tet(Q) genes were detected. However, a tet(M) like sequence was identified in all Tn5253 positive strains and was found associated to Tn916 composite. Only one isolate was phenotypically resistant to chloramphenicol, wherein a chloramphenicol acetyl transferase (cat) gene sequence homologous to cat(pC194) from the Staphylococcus aureus plasmid pC194 was detected. In conclusion, clinical Streptococcus pneumoniae type 1 isolated during 2002 to 2009 meningitis surveillance in Niger were fully susceptible to macrolides and quinolones but highly resistant to tetracycline (77.4%) through acquisition of a defective Tn5253 like element composed of Tn5252 and Tn916 transposons. Of the 31 tested isolates, only one was exceptionally resistant to chloramphenicol and carried a Tn5253 transposon that contained cat gene sequence.