Advances in Pneumococcal Antibiotic Resistance

Jae-Hoon Song


Expert Rev Resp Med. 2013;7(5):491-498. 

In This Article

Relationship Between Serotype 19A and Antimicrobial Resistance

Emergence of non-vaccine serotypes, predominantly 19A, was associated with increasing prevalence of antimicrobial resistance.[11] According to recent data from the United States, 93.2% of penicillin nonsusceptible isolates causing IPD showed non-PCV7 serotypes, and 53.2% of these isolates was serotype19A.[63] ANSORP study in 2008–2009 showed that 28.1% of penicillin nonsusceptible isolates was serotype 19A in Asian countries.[14] In addition, 86% of serotype 19A isolates were resistant to macrolide (78.3% of 19A isolates carried both ermB and mefA genes) and 79.8% showed MDR, suggesting that the prominent increase in serotype 19A would be one of the major reasons for a high prevalence of macrolide resistance and MDR in Asian countries.

Most of serotype 19A S. pneumoniae isolates belonged to CC320, which originated from the MDR Taiwan19F-14 Pneumococcal Molecular Epidemiology Network clone (a double-locus variant of Taiwan19F-14), in many parts of the world.[11,38] According to the ANSORP study, MDR ST320 was the most prevalent clone among 19A S. pneumoniae isolates from Asian countries.[64] In the United States, emergence of MDR CC320 has contributed to the increase in serotype 19A after the introduction of PCV7, while expansion of CC199, which had already been present before the introduction of PCV7, also affected in the increase of serotype 19A.[25] According the Active Bacterial Core Surveillance Program, serotype 19A belonging to CC320/271 has significantly increased from 20.9% in 2005 to 32.7% in 2007 in the United States, which is consistent with the increase of penicillin-resistant serotype 19A pneumococci during the period (82% of penicillin-resistant serotype 19A isolates belonged to CC320/271 in 2007), while CC199 has decreased from 58.9% in 2005 to 40.3% in 2007.[65] Another study by the United States Pediatric Multicenter Pneumococcal Surveillance Group also showed that the emergence of CC320 was associated with major increase in multidrug-resistant 19A strains which was still predominant after the introduction of PCV13.[66] In Norway, where antibiotic use is restricted by national prescription policy, penicillin-susceptible serotype 19A pneumococcal strains dominated after the introduction of PCV7 in 2006, which was caused by expansion of drug-susceptible CC199.[67] Therefore, it is likely that antibiotic pressure and introduction of PCV may be the most important factors for emergence of MDR 19A strains.

Since PCV13 includes serotype 19A, it may contribute to the reduction of the clonal spread of MDR 19A S. pneumoniae strains, although much data are not available yet. There might be another possibilities for the emergence of novel serotypes that are not included in the PCV13 such as 6C, 11, 15A, 33A or 35B.[29,68] Recently, extensively drug-resistant serotype 11A S. pneumoniae isolate (ST8279), which was nonsusceptible to at least one agent in all antibiotic classes except vancomycin and linezolid, was reported from Korea.[69] Also, serotype 6D, which have been recently identified in some countries, is relatively prevalent in Korea and multidrug-resistant ST282 clone was predominant in Korea, although its clinical impact is unknown.[70] Therefore, surveillance studies will be needed to evaluate the effect of PCV13 vaccination on the serotype distribution and antimicrobial resistance in S. pneumoniae in the future.