be a non-vaccine type (NVT) serotype 19A. This is consistent with the well-documented serotype switch in S. pneumoniae isolates in the U.S. [35, 36]. Figure 1 Changes in population structure over time in dual mef (E)/ erm (B)-positive, mef (E)-positive, and erm (B)-positive S. pneumoniae clinical isolates. No isolates positive for mef(E) or erm(B) genes were collected in 2001-2002. ST, sequence type; NF, sequence type not found; NT, not typed Sequence types and serotypes of the mef(E)-positive population remained diverse over the time period (Table 2, Figure 1). Out of 20 total sequence types identified in this population, only six were found in more than one two-year period, three of those in both pre- and post-vaccine introduction time periods. These include ST236, serotype 19 F, the genotype of the highly dispersed Taiwan19F-14 clone and likely ancestor to the CC271 lineages, ST376 of NVT 6A, and ST156, the genotype of the Spain9V-3 clone in which serotype switching from VT 9 V to NVT 19A has been documented [35]. Interestingly,
in the pre-vaccination time period, the ST156 strain is serotype 6A while the strain from the post-vaccination time period likely BV-6 manufacturer is 9 V. (PCR deduction typed the strain as 9 V or 9 F.) The former was isolated from a 70 year-old male who may have Baricitinib received the 23-valent polysaccharide pneumococcal vaccine (PPSV) intended for adults over 65 years old and high-risk groups, and which covers serotype 9
V. This strain may have switched from 9 V to 6A in response to PPSV, before introduction of PCV7. Additionally, the mef(E)-positive population illustrates serotype replacement. Historically VT strains caused most pneumococcal disease, however after 2000, more NVT strains than VT strains were found. In the erm(B)-positive population, serotype replacement may also be evident. The early population is comprised of two ST315, VT 6B strains and a ST3066 strain, possibly VT 18 C. (This isolate typed as 18A, B, C, or F using PCR; the Pneumococcal Molecular Epidemiology Network [PMEN] clone database links ST3066 with serotype 18 C [37].) They were replaced in later years by the unrelated ST63, NVT 15A or 15 F (PMEN links ST63 with serotype 15A [37]) and ST180, NVT 3 (Table 2, Figure 1). mef(E) and erm(B) population characteristics: Specimen types Many (n = 32) of the dual mef(E)/erm(B)-positive isolates were from ear specimens collected after 2000 (post-PCV7) from children of vaccine age (less than five years old after the introduction of the PCV7 in 2000). Many (n = 32) were from respiratory specimens, only eight of which came from children of vaccine age; most came from adults post-PCV7.