Molecular characterisation of multidrug-resistant pneumococcal clones colonising healthy children in Mérida, Venezuela.

Genetic mechanisms of resistance, clonal composition and the occurrence of pili were analysed in 48 multidrug-resistant (MDR) pneumococci isolated from healthy children in Mérida, Venezuela. Intermediate resistance to penicillin was related to variations in pbp2b and pbp2x. High-level resistance to penicillin as well as low susceptibility to cephalosporins and carbapenems were associated with alterations in pbp1a, pbp2b and pbp2x. Non-β-lactam resistance was associated with Tn3872, Tn5253, Tn6002 and Tn2010 transposons. Macrolide-resistant strains carried ermB or mefE, but not mefA. Tetracycline- and chloramphenicol-resistant pneumococci carried tetM and cat, respectively. MDR pneumococci were related to six clonal complexes (CCs), largely CC156 or CC15. Limited diversity in pbp2a,2b,2x-RFLP profiles within each clone was observed. Conversely, detection of non-β-lactam resistance and transposons revealed clear genetic diversity within clones. A group of non-typeable/cpsA-negative pneumococci related to the null capsule clade 1 (NCC1) carrying a Tn2009 element was found. Each NCC1-related strain showed a novel MLST allelic combination and a different pbp2a,2b,2x-RFLP profile. PI-1 (pilus type 1 rrgC gene) was present in most of the MDR pneumococci and its occurrence was commonly homogeneous within each clone. PI-1 was present in all CC242 and CC320 pneumococci, whereas it was absent in all CC37, CC81 and NCC1 isolates. CC156 and CC15 isolates showed variations in the occurrence of PI-1. Both PI-1 and the islet for pilus type 2 were present in CC320 isolates. We provide useful data to follow the evolution of clonal composition, mechanisms of antibiotic resistance and the occurrence of pili among pneumococci circulating in Mérida.