High Rate of Serotype Switching and Genetic Variations Indicates Widespread Recombination Between Clinical and Commensal Penicillin-Nonsusceptible Streptococcus pneumoniae in Tehran

A total of 161 Streptococcus pneumoniae were collected between 2013 and 2015 in Tehran, Iran. The strains were tested for antimicrobial susceptibility and minimum inhibitory concentrations, serotyped, and genotyped by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Penicillin-binding proteins (PBPs) were also typed by restriction fragment length polymorphism (PBP-RFLP). Out of 161 strains, 32 isolates (20%) were highly resistant to penicillin. The most frequent serotypes among the penicillin-nonsusceptible S. pneumoniae (PNSP) were 14 (24%), 23F (18%), and 19F (17%). RFLP of pbp2b, pbp2x, and pbp1a genes revealed 8, 6, and 7 different patterns, respectively. Analysis of 93 PNSP isolates displayed 80 PFGE types with 8 common types constituting 21 (23%) isolates. The remaining 72 isolates (77%) were single types. MLST indicated a high degree of genetic diversity among the 93 PNSP with 36 different sequence types. Six internationally known penicillin resistant clones were identified in our isolates among which Spain(23F)-1 (ST81), Spain(6B)-2 (ST90), and Spain(9V)-3 (ST156) were the predominant clones. The results indicated international identifiable clones of S. pneumoniae, especially Spain(23F)-1 with high penicillin resistance could play a major role in spread of antimicrobial resistance in Iran. The extensive sequence variation in PBP2x, PBP2b, and PBP1a in resistant strains of clinical and commensal S. pneumoniae was suggestive of a widespread homologous recombination within S. pneumoniae populations.